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Net::SSLeay(3pm)      User Contributed Perl Documentation      Net::SSLeay(3pm)

NAME
       Net::SSLeay - Perl bindings for OpenSSL and LibreSSL

SYNOPSIS
           use Net::SSLeay qw(get_https post_https sslcat make_headers make_form);

           ($page) = get_https('www.bacus.pt', 443, '/');                 # Case 1

           ($page, $response, %reply_headers)
               = get_https('www.bacus.pt', 443, '/',                      # Case 2
                   make_headers(User-Agent => 'Cryptozilla/5.0b1',
                                Referer    => 'https://www.bacus.pt')
                 );

           ($page, $result, %headers)                                     # Case 2b
               = get_https('www.bacus.pt', 443, '/protected.html',
                   make_headers(Authorization =>
                       'Basic ' . MIME::Base64::encode("$user:$pass",''))
                 );

           ($page, $response, %reply_headers)
               = post_https('www.bacus.pt', 443, '/foo.cgi', '',          # Case 3
                   make_form(OK => '1', name => 'Sampo')
                 );

           $reply = sslcat($host, $port, $request);                       # Case 4

           ($reply, $err, $server_cert) = sslcat($host, $port, $request); # Case 5

           $Net::SSLeay::trace = 2; # 0=no debugging, 1=ciphers, 2=trace, 3=dump data

           Net::SSLeay::initialize(); # Initialize ssl library once

DESCRIPTION
       This module provides Perl bindings for libssl (an SSL/TLS API) and
       libcrypto (a cryptography API).

COMPATIBILITY
       Net::SSLeay supports the following libssl implementations:

       •   Any stable release of OpenSSL <https://www.openssl.org> in the 0.9.8
           - 3.2 branches, except for OpenSSL 0.9.8 - 0.9.8b.

       •   Any stable release of LibreSSL <https://www.libressl.org> in the 2.0
           - 3.8 series, except for LibreSSL 3.2.2 and 3.2.3.

       Net::SSLeay  may  not  function as expected with releases other than the
       ones listed above due to libssl API incompatibilities, or, in  the  case
       of LibreSSL, because of deviations from the libssl API.

       Net::SSLeay  is  only  as secure as the underlying libssl implementation
       you use.  Although Net::SSLeay maintains compatibility with old versions
       of OpenSSL and LibreSSL, it is  strongly  recommended  that  you  use  a
       version of OpenSSL or LibreSSL that is supported by the OpenSSL/LibreSSL
       developers   and/or  your  operating  system  vendor.  Many  unsupported
       versions of OpenSSL and LibreSSL are known to  contain  severe  security
       vulnerabilities.    Refer    to    the    OpenSSL    Release    Strategy
       <https://www.openssl.org/policies/releasestrat.html>    and     LibreSSL
       Support     Schedule     <https://www.libressl.org/releases.html>    for
       information on which versions are currently supported.

       The libssl API has changed significantly since OpenSSL  0.9.8:  hundreds
       of  functions  have been added, deprecated or removed in the intervening
       versions.  Although this documentation lists all of  the  functions  and
       constants  that  Net::SSLeay  may expose, they will not be available for
       use if they are missing from the underlying libssl implementation. Refer
       to the compatibility  notes  in  this  documentation,  as  well  as  the
       OpenSSL/LibreSSL manual pages, for information on which OpenSSL/LibreSSL
       versions  support  each function or constant. At run-time, you can check
       whether a function or constant is exposed before calling  it  using  the
       following convention:

           if ( defined &Net::SSLeay::libssl_function ) {
               # libssl_function() (or SSL_libssl_function()) is available
               Net::SSLeay::libssl_function(...);
           }

OVERVIEW
       Net::SSLeay module basically comprise of:

       •   High level functions for accessing web servers (by using HTTP/HTTPS)

       •   Low level API (mostly mapped 1:1 to openssl's C functions)

       •   Convenience  functions  (related to low level API but with more perl
           friendly interface)

       There is also a related module called  Net::SSLeay::Handle  included  in
       this distribution that you might want to use instead. It has its own pod
       documentation.

   High level functions for accessing web servers
       This  module  offers some high level convenience functions for accessing
       web pages on SSL servers (for symmetry, the  same  API  is  offered  for
       accessing  http servers, too), an sslcat() function for writing your own
       clients, and finally access to the SSL api of the SSLeay/OpenSSL package
       so you can write servers or clients for more complicated applications.

       For high level functions it is most convenient to import them into  your
       main namespace as indicated in the synopsis.

       Basic set of functions

       •   get_https

       •   post_https

       •   put_https

       •   head_https

       •   do_https

       •   sslcat

       •   https_cat

       •   make_form

       •   make_headers

       Case  1 (in SYNOPSIS) demonstrates the typical invocation of get_https()
       to fetch an HTML page from secure server. The  first  argument  provides
       the  hostname  or  IP in dotted decimal notation of the remote server to
       contact. The second argument is the TCP port at the remote end (your own
       port is picked arbitrarily from high numbered ports as usual  for  TCP).
       The third argument is the URL of the page without the host name part. If
       in doubt consult the HTTP specifications at <https://www.w3c.org>.

       Case  2  (in  SYNOPSIS) demonstrates full fledged use of get_https(). As
       can be seen, get_https() parses the response and  response  headers  and
       returns  them  as  a  list,  which  can  be captured in a hash for later
       reference. Also a fourth argument to get_https() is used to insert  some
       additional  headers  in  the  request. make_headers() is a function that
       will convert a list or hash to  such  headers.  By  default  get_https()
       supplies  "Host" (to make virtual hosting easy) and "Accept" (reportedly
       needed by IIS) headers.

       Case 2b (in SYNOPSIS) demonstrates how to get a password protected page.
       Refer to the HTTP protocol  specifications  for  further  details  (e.g.
       RFC-2617).

       Case 3 (in SYNOPSIS) invokes post_https() to submit a HTML/CGI form to a
       secure  server.  The first four arguments are equal to get_https() (note
       that the empty string ('') is passed as  header  argument).   The  fifth
       argument  is  the  contents  of  the  form  formatted  according  to CGI
       specification.  Do not post UTF-8 data as content:  use  utf8::downgrade
       first.  In  this case the helper function make_https() is used to do the
       formatting, but you could pass any  string.  post_https()  automatically
       adds "Content-Type" and "Content-Length" headers to the request.

       Case  4  (in SYNOPSIS) shows the fundamental sslcat() function (inspired
       in spirit by the "netcat" utility :-). It's your swiss army  knife  that
       allows  you  to easily contact servers, send some data, and then get the
       response. You are responsible for formatting the data  and  parsing  the
       response - sslcat() is just a transport.

       Case  5  (in SYNOPSIS) is a full invocation of sslcat() which allows the
       return of errors as well as the server (peer) certificate.

       The $trace global variable can be used to control the verbosity  of  the
       high  level functions. Level 0 guarantees silence, level 1 (the default)
       only emits error messages.

       Alternate versions of high-level API

       •   get_https3

       •   post_https3

       •   put_https3

       •   get_https4

       •   post_https4

       •   put_https4

       The above mentioned functions actually return the response headers as  a
       list, which only gets converted to hash upon assignment (this assignment
       looses  information  if the same header occurs twice, as may be the case
       with cookies). There are also  other  variants  of  the  functions  that
       return unprocessed headers and that return a reference to a hash.

           ($page, $response, @headers) = get_https('www.bacus.pt', 443, '/');
           for ($i = 0; $i < $#headers; $i+=2) {
               print "$headers[$i] = " . $headers[$i+1] . "\n";
           }

           ($page, $response, $headers, $server_cert)
               = get_https3('www.bacus.pt', 443, '/');
           print "$headers\n";

           ($page, $response, $headers_ref)
               = get_https4('www.bacus.pt', 443, '/');
           for $k (sort keys %{$headers_ref}) {
               for $v (@{$$headers_ref{$k}}) {
                   print "$k = $v\n";
               }
           }

       All  of  the above code fragments accomplish the same thing: display all
       values of all headers. The  API  functions  ending  in  "3"  return  the
       headers  simply  as  a  scalar string and it is up to the application to
       split them up. The functions ending in "4" return a reference to a  hash
       of  arrays (see perlref and perllol if you are not familiar with complex
       perl data structures). To access a single value of such  a  header  hash
       you would do something like

           print $$headers_ref{COOKIE}[0];

       Variants  3  and  4 also allow you to discover the server certificate in
       case you would like to store or display it, e.g.

           ($p, $resp, $hdrs, $server_cert) = get_https3('www.bacus.pt', 443, '/');
           if (!defined($server_cert) || ($server_cert == 0)) {
               warn "Subject Name: undefined, Issuer  Name: undefined";
           } else {
               warn sprintf('Subject Name: %s Issuer  Name: %s',
                   Net::SSLeay::X509_NAME_oneline(
                       Net::SSLeay::X509_get_subject_name($server_cert)),
                   Net::SSLeay::X509_NAME_oneline(
                       Net::SSLeay::X509_get_issuer_name($server_cert))
               );
           }

       Beware that this method only allows after the fact verification  of  the
       certificate: by the time get_https3() has returned the https request has
       already  been sent to the server, whether you decide to trust it or not.
       To do the verification correctly you  must  either  employ  the  OpenSSL
       certificate  verification  framework or use the lower level API to first
       connect and verify the certificate and only then send the http data. See
       the implementation of ds_https3() for guidance on how to do this.

       Using client certificates

       Secure web communications are  encrypted  using  symmetric  crypto  keys
       exchanged  using  encryption  based  on  the  certificate of the server.
       Therefore in all SSL connections the server  must  have  a  certificate.
       This  serves  both  to  authenticate  the  server  to the clients and to
       perform the key exchange.

       Sometimes it is necessary  to  authenticate  the  client  as  well.  Two
       options  are  available:  HTTP  basic  authentication  and a client side
       certificate. The basic authentication over HTTPS is actually quite  safe
       because HTTPS guarantees that the password will not travel in the clear.
       Never-the-less,  problems  like  easily  guessable passwords remain. The
       client certificate method involves authentication of the client  at  the
       SSL level using a certificate. For this to work, both the client and the
       server  have  certificates  (which  typically are different) and private
       keys.

       The API functions outlined above accept additional arguments that  allow
       one  to  supply the client side certificate and key files. The format of
       these files is the same as used for server certificates and  the  caveat
       about encrypting private keys applies.

           ($page, $result, %headers)                                     # 2c
               = get_https('www.bacus.pt', 443, '/protected.html',
                   make_headers(Authorization =>
                       'Basic ' . MIME::Base64::encode("$user:$pass",'')),
                   '', $mime_type6, $path_to_crt7, $path_to_key8
                 );

           ($page, $response, %reply_headers)
               = post_https('www.bacus.pt', 443, '/foo.cgi',              # 3b
                   make_headers('Authorization' =>
                       'Basic ' . MIME::Base64::encode("$user:$pass",'')),
                   make_form(OK   => '1', name => 'Sampo'),
                   $mime_type6, $path_to_crt7, $path_to_key8
                 );

       Case  2c  (in  SYNOPSIS)  demonstrates getting a password protected page
       that also requires a client certificate, i.e. it is possible to use both
       authentication methods simultaneously.

       Case 3b (in SYNOPSIS) is a full blown  POST  to  a  secure  server  that
       requires  both  password  authentication  and a client certificate, just
       like in case 2c.

       Note: The client will not send a certificate unless the server  requests
       one.   This  is  typically  achieved  by  setting  the  verify  mode  to
       "VERIFY_PEER" on the server:

           Net::SSLeay::set_verify($ssl, Net::SSLeay::VERIFY_PEER, 0);

       See  "perldoc  ~openssl/doc/ssl/SSL_CTX_set_verify.pod"   for   a   full
       description.

       Working through a web proxy

       •   set_proxy

       "Net::SSLeay"  can  use a web proxy to make its connections. You need to
       first set the proxy host and port using set_proxy() and  then  just  use
       the normal API functions, e.g:

           Net::SSLeay::set_proxy('gateway.myorg.com', 8080);
           ($page) = get_https('www.bacus.pt', 443, '/');

       If  your  proxy  requires  authentication, you can supply a username and
       password as well

           Net::SSLeay::set_proxy('gateway.myorg.com', 8080, 'joe', 'salainen');
           ($page, $result, %headers)
               = get_https('www.bacus.pt', 443, '/protected.html',
                   make_headers(Authorization =>
                       'Basic ' . MIME::Base64::encode("susie:pass",''))
                 );

       This example demonstrates the case where we authenticate to the proxy as
       "joe" and to the final  web  server  as  "susie".  Proxy  authentication
       requires the "MIME::Base64" module to work.

       HTTP (without S) API

       •   get_http

       •   post_http

       •   tcpcat

       •   get_httpx

       •   post_httpx

       •   tcpxcat

       Over  the  years  it has become clear that it would be convenient to use
       the light-weight flavour API of "Net::SSLeay" for normal  HTTP  as  well
       (see  "LWP"  for  the heavy-weight object-oriented approach). In fact it
       would be nice to be able to flip https on  and  off  on  the  fly.  Thus
       regular HTTP support was evolved.

           use Net::SSLeay qw(get_http post_http tcpcat
                              get_httpx post_httpx tcpxcat
                              make_headers make_form);

           ($page, $result, %headers)
               = get_http('www.bacus.pt', 443, '/protected.html',
                   make_headers(Authorization =>
                       'Basic ' . MIME::Base64::encode("$user:$pass",''))
                 );

           ($page, $response, %reply_headers)
               = post_http('www.bacus.pt', 443, '/foo.cgi', '',
                   make_form(OK => '1', name => 'Sampo')
                 );

           ($reply, $err) = tcpcat($host, $port, $request);

           ($page, $result, %headers)
               = get_httpx($usessl, 'www.bacus.pt', 443, '/protected.html',
                   make_headers(Authorization =>
                       'Basic ' . MIME::Base64::encode("$user:$pass",''))
                 );

           ($page, $response, %reply_headers)
               = post_httpx($usessl, 'www.bacus.pt', 443, '/foo.cgi', '',
                   make_form(OK => '1',  name => 'Sampo')
                 );

           ($reply, $err, $server_cert) = tcpxcat($usessl, $host, $port, $request);

       As  can  be  seen,  the "x" family of APIs takes as the first argument a
       flag which indicates whether SSL is used or not.

   Certificate verification and Certificate Revocation Lists (CRLs)
       OpenSSL supports the ability to verify peer certificates.  It  can  also
       optionally  check  the peer certificate against a Certificate Revocation
       List (CRL) from the certificates issuer. A CRL is a file, created by the
       certificate issuer that lists all the certificates  that  it  previously
       signed, but which it now revokes. CRLs are in PEM format.

       You can enable "Net::SSLeay CRL" checking like this:

           &Net::SSLeay::X509_STORE_set_flags(
               &Net::SSLeay::CTX_get_cert_store($ssl),
               &Net::SSLeay::X509_V_FLAG_CRL_CHECK
           );

       After setting this flag, if OpenSSL checks a peer's certificate, then it
       will attempt to find a CRL for the issuer. It does this by looking for a
       specially   named   file   in   the   search   directory   specified  by
       CTX_load_verify_locations.  CRL files are named with  the  hash  of  the
       issuer's  subject  name,  followed  by  ".r0",  ".r1"  etc.  For example
       "ab1331b2.r0", "ab1331b2.r1". It will read all  the  .r  files  for  the
       issuer,  and  then check for a revocation of the peer certificate in all
       of them.  (You can also force it to look in a specific named CRL  file.,
       see  below).   You can find out the hash of the issuer subject name in a
       CRL with

           openssl crl -in crl.pem -hash -noout

       If the peer certificate does not pass the revocation list, or if no  CRL
       is found, then the handshaking fails with an error.

       You  can  also force OpenSSL to look for CRLs in one or more arbitrarily
       named files.

           my $bio = Net::SSLeay::BIO_new_file($crlfilename, 'r');
           my $crl = Net::SSLeay::PEM_read_bio_X509_CRL($bio);
           if ($crl) {
               Net::SSLeay::X509_STORE_add_crl(
                      Net::SSLeay::CTX_get_cert_store($ssl, $crl)
               );
           } else {
               # error reading CRL....
           }

       Usually the URLs where you can download the CRLs  is  contained  in  the
       certificate itself and you can extract them with

           my @url = Net::SSLeay::P_X509_get_crl_distribution_points($cert);

       But  there  is no automatic downloading of the CRLs and often these CRLs
       are too huge to just download  them  to  verify  a  single  certificate.
       Also,  these  CRLs  are often in DER format which you need to convert to
       PEM before you can use it:

           openssl crl -in crl.der -inform der -out crl.pem

       So as an alternative for faster and timely revocation checks you  better
       use the Online Status Revocation Protocol (OCSP).

   Certificate verification and Online Status Revocation Protocol (OCSP)
       While  checking  for  revoked  certificates  is  possible  and fast with
       Certificate Revocation Lists, you need  to  download  the  complete  and
       often huge list before you can verify a single certificate.

       A  faster  way is to ask the CA to check the revocation of just a single
       or a few certificates  using  OCSP.  Basically  you  generate  for  each
       certificate  an  OCSP_CERTID  based  on  the  certificate itself and its
       issuer, put the ids together into an OCSP_REQUEST and send  the  request
       to the URL given in the certificate.

       As  a  result you get back an OCSP_RESPONSE and need to check the status
       of the response, check that it is valid (e.g.  signed  by  the  CA)  and
       finally  extract  the  information about each OCSP_CERTID to find out if
       the certificate is still valid or got revoked.

       With Net::SSLeay this can be done like this:

           # get id(s) for given certs, like from get_peer_certificate
           # or get_peer_cert_chain. This will croak if
           # - one tries to make an OCSP_CERTID for a self-signed certificate
           # - the issuer of the certificate cannot be found in the SSL objects
           #   store, nor in the current certificate chain
           my $cert = Net::SSLeay::get_peer_certificate($ssl);
           my $id = eval { Net::SSLeay::OCSP_cert2ids($ssl,$cert) };
           die "failed to make OCSP_CERTID: $@" if $@;

           # create OCSP_REQUEST from id(s)
           # Multiple can be put into the same request, if the same OCSP responder
           # is responsible for them.
           my $req = Net::SSLeay::OCSP_ids2req($id);

           # determine URI of OCSP responder
           my $uri = Net::SSLeay::P_X509_get_ocsp_uri($cert);

           # Send stringified OCSP_REQUEST with POST to $uri.
           # We can ignore certificate verification for https, because the OCSP
           # response itself is signed.
           my $ua = HTTP::Tiny->new(verify_SSL => 0);
           my $res = $ua->request( 'POST',$uri, {
               headers => { 'Content-type' => 'application/ocsp-request' },
               content => Net::SSLeay::i2d_OCSP_REQUEST($req)
           });
           my $content = $res && $res->{success} && $res->{content}
               or die "query failed";

           # Extract OCSP_RESPONSE.
           # this will croak if the string is not an OCSP_RESPONSE
           my $resp = eval { Net::SSLeay::d2i_OCSP_RESPONSE($content) };

           # Check status of response.
           my $status = Net::SSLeay::OCSP_response_status($resp);
           if ($status != Net::SSLeay::OCSP_RESPONSE_STATUS_SUCCESSFUL()) {
               die "OCSP response failed: " .
                   Net::SSLeay::OCSP_response_status_str($status);
           }

           # Verify signature of response and if nonce matches request.
           # This will croak if there is a nonce in the response, but it does not match
           # the request. It will return false if the signature could not be verified,
           # in which case details can be retrieved with Net::SSLeay::ERR_get_error.
           # It will not complain if the response does not contain a nonce, which is
           # usually the case with pre-signed responses.
           if ( ! eval { Net::SSLeay::OCSP_response_verify($ssl,$resp,$req) }) {
               die "OCSP response verification failed";
           }

           # Extract information from OCSP_RESPONSE for each of the ids.

           # If called in scalar context it will return the time (as time_t), when the
           # next update is due (minimum of all successful responses inside $resp). It
           # will croak on the following problems:
           # - response is expired or not yet valid
           # - no response for given OCSP_CERTID
           # - certificate status is not good (e.g. revoked or unknown)
           if ( my $nextupd = eval { Net::SSLeay::OCSP_response_results($resp,$id) }) {
               warn "certificate is valid, next update in " .
                   ($nextupd-time()) . " seconds\n";
           } else {
               die "certificate is not valid: $@";
           }

           # But in array context it will return detailed information about each given
           # OCSP_CERTID instead croaking on errors:
           # if no @ids are given it will return information about all single responses
           # in the OCSP_RESPONSE
           my @results = Net::SSLeay::OCSP_response_results($resp,@ids);
           for my $r (@results) {
               print Dumper($r);
               # @results are in the same order as the @ids and contain:
               # $r->[0] - OCSP_CERTID
               # $r->[1] - undef if no error (certificate good) OR error message as string
               # $r->[2] - hash with details:
               #   thisUpdate - time_t of this single response
               #   nextUpdate - time_t when update is expected
               #   statusType - integer:
               #      V_OCSP_CERTSTATUS_GOOD(0)
               #      V_OCSP_CERTSTATUS_REVOKED(1)
               #      V_OCSP_CERTSTATUS_UNKNOWN(2)
               #   revocationTime - time_t (only if revoked)
               #   revocationReason - integer (only if revoked)
               #   revocationReason_str - reason as string (only if revoked)
           }

       To further speed up certificate revocation checking one can  use  a  TLS
       extension to instruct the server to staple the OCSP response:

           # set TLS extension before doing SSL_connect
           Net::SSLeay::set_tlsext_status_type($ssl,
               Net::SSLeay::TLSEXT_STATUSTYPE_ocsp());

           # setup callback to verify OCSP response
           my $cert_valid = undef;
           Net::SSLeay::CTX_set_tlsext_status_cb($context,sub {
               my ($ssl,$resp) = @_;
               if (!$resp) {
                   # Lots of servers don't return an OCSP response.
                   # In this case we must check the OCSP status outside the SSL
                   # handshake.
                   warn "server did not return stapled OCSP response\n";
                   return 1;
               }
               # verify status
               my $status = Net::SSLeay::OCSP_response_status($resp);
               if ($status != Net::SSLeay::OCSP_RESPONSE_STATUS_SUCCESSFUL()) {
                   warn "OCSP response failure: $status\n";
                   return 1;
               }
               # verify signature - we have no OCSP_REQUEST here to check nonce
               if (!eval { Net::SSLeay::OCSP_response_verify($ssl,$resp) }) {
                   warn "OCSP response verify failed\n";
                   return 1;
               }
               # check if the certificate is valid
               # we should check here against the peer_certificate
               my $cert = Net::SSLeay::get_peer_certificate();
               my $certid = eval { Net::SSLeay::OCSP_cert2ids($ssl,$cert) } or do {
                   warn "cannot get certid from cert: $@";
                   $cert_valid = -1;
                   return 1;
               };

               if ( $nextupd = eval {
                   Net::SSLeay::OCSP_response_results($resp,$certid) }) {
                   warn "certificate not revoked\n";
                   $cert_valid = 1;
               } else {
                   warn "certificate not valid: $@";
                   $cert_valid = 0;
               }
           });

           # do SSL handshake here
           # ....
           # check if certificate revocation was checked already
           if ( ! defined $cert_valid) {
               # check revocation outside of SSL handshake by asking OCSP responder
               ...
           } elsif ( ! $cert_valid ) {
               die "certificate not valid - closing SSL connection";
           } elsif ( $cert_valid<0 ) {
               die "cannot verify certificate revocation - self-signed ?";
           } else {
               # everything fine
               ...
           }

   Using Net::SSLeay in multi-threaded applications
       IMPORTANT: versions 1.42 or earlier are not thread-safe!

       Net::SSLeay module implements all necessary stuff to be ready for multi-
       threaded   environment   -  it  requires  openssl-0.9.7  or  newer.  The
       implementation fully  follows  thread  safety  related  requirements  of
       openssl                                                      library(see
       <https://www.openssl.org/docs/manmaster/man3/threads.html>).

       If you are about to use  Net::SSLeay  (or  any  other  module  based  on
       Net::SSLeay)  in  multi-threaded  perl  application it is recommended to
       follow this best-practice:

       Initialization

       Load and initialize Net::SSLeay module in the main thread:

           use threads;
           use Net::SSLeay;

           Net::SSLeay::load_error_strings();
           Net::SSLeay::SSLeay_add_ssl_algorithms();
           Net::SSLeay::randomize();

           sub do_master_job {
               # ... call whatever from Net::SSLeay
           }

           sub do_worker_job {
               # ... call whatever from Net::SSLeay
           }

           # start threads
           my $master  = threads->new(\&do_master_job, 'param1', 'param2');
           my @workers = threads->new(\&do_worker_job, 'arg1', 'arg2') for (1..10);

           # waiting for all threads to finish
           $_->join() for (threads->list);

       NOTE: Openssl's "int SSL_library_init(void)"  function  (which  is  also
       aliased as "SSLeay_add_ssl_algorithms", "OpenSSL_add_ssl_algorithms" and
       "add_ssl_algorithms")  is  not re-entrant and multiple calls can cause a
       crash in threaded application.  Net::SSLeay implements flags  preventing
       repeated  calls to this function, therefore even multiple initialization
       via   Net::SSLeay::SSLeay_add_ssl_algorithms()   should   work   without
       trouble.

       Using callbacks

       Do  not  use  callbacks  across  threads (the module blocks cross-thread
       callback operations and throws a warning). Always do the callback setup,
       callback use and callback destruction within the same thread.

       Using openssl elements

       All openssl elements (X509, SSL_CTX, ...) can be directly passed between
       threads.

           use threads;
           use Net::SSLeay;

           Net::SSLeay::load_error_strings();
           Net::SSLeay::SSLeay_add_ssl_algorithms();
           Net::SSLeay::randomize();

           sub do_job {
               my $context = shift;
               Net::SSLeay::CTX_set_default_passwd_cb($context, sub { "secret" });
               # ...
           }

           my $c = Net::SSLeay::CTX_new();
           threads->create(\&do_job, $c);

       Or:

           use threads;
           use Net::SSLeay;

           my $context; # does not need to be 'shared'

           Net::SSLeay::load_error_strings();
           Net::SSLeay::SSLeay_add_ssl_algorithms();
           Net::SSLeay::randomize();

           sub do_job {
               Net::SSLeay::CTX_set_default_passwd_cb($context, sub { "secret" });
               # ...
           }

           $context = Net::SSLeay::CTX_new();
           threads->create(\&do_job);

       Using other perl modules based on Net::SSLeay

       It should be fine to use any other module  based  on  Net::SSLeay  (like
       IO::Socket::SSL)   in   multi-threaded  applications.  It  is  generally
       recommended to do any global initialization of such a module in the main
       thread before calling "threads->new(..)" or "threads->create(..)" but it
       might differ module by module.

       To be safe you can load and init  Net::SSLeay  explicitly  in  the  main
       thread:

           use Net::SSLeay;
           use Other::SSLeay::Based::Module;

           Net::SSLeay::load_error_strings();
           Net::SSLeay::SSLeay_add_ssl_algorithms();
           Net::SSLeay::randomize();

       Or even safer:

           use Net::SSLeay;
           use Other::SSLeay::Based::Module;

           BEGIN {
               Net::SSLeay::load_error_strings();
               Net::SSLeay::SSLeay_add_ssl_algorithms();
               Net::SSLeay::randomize();
           }

       Combining Net::SSLeay with other modules linked with openssl

       BEWARE:  This  might be a big trouble! This is not guaranteed be thread-
       safe!

       There are many other (XS) modules linked  directly  to  openssl  library
       (like Crypt::SSLeay).

       As   it   is   expected   that   also   "another"   module   will   call
       "SSLeay_add_ssl_algorithms" at some point we have again a  trouble  with
       multiple openssl initialization by Net::SSLeay and "another" module.

       As   you   can   expect  Net::SSLeay  is  not  able  to  avoid  multiple
       initialization of openssl library called by "another" module,  thus  you
       have  to handle this on your own (in some cases it might not be possible
       at all to avoid this).

       Threading with get_https and friends

       The convenience functions get_https, post_https etc all  initialize  the
       SSL   library   by   calling   Net::SSLeay::initialize  which  does  the
       conventional library initialization:

           Net::SSLeay::load_error_strings();
           Net::SSLeay::SSLeay_add_ssl_algorithms();
           Net::SSLeay::randomize();

       Net::SSLeay::initialize initializes the SSL library at most  once.   You
       can  override  the  Net::SSLeay::initialize  function if you desire some
       other type of initialization behaviour by get_https  and  friends.   You
       can  call  Net::SSLeay::initialize from your own code if you desire this
       conventional library initialization.

   Convenience routines
       To be used with Low level API

           Net::SSLeay::randomize($rn_seed_file,$additional_seed);
           Net::SSLeay::set_cert_and_key($ctx, $cert_path, $key_path);
           $cert = Net::SSLeay::dump_peer_certificate($ssl);
           Net::SSLeay::ssl_write_all($ssl, $message) or die "ssl write failure";
           $got = Net::SSLeay::ssl_read_all($ssl) or die "ssl read failure";

           $got = Net::SSLeay::ssl_read_CRLF($ssl [, $max_length]);
           $got = Net::SSLeay::ssl_read_until($ssl [, $delimit [, $max_length]]);
           Net::SSLeay::ssl_write_CRLF($ssl, $message);

       •   randomize

           seeds  the  openssl  PRNG  with  "/dev/urandom"  (see  the  top   of
           "SSLeay.pm" for how to change or configure this) and optionally with
           user  provided  data.  It  is  very  important to properly seed your
           random numbers, so do not forget to call this. The  high  level  API
           functions  automatically  call  randomize() so it is not needed with
           them. See also caveats.

       •   set_cert_and_key

           takes two file names as  arguments  and  sets  the  certificate  and
           private  key  to  those.  This  can  be  used  to  set either server
           certificates or client certificates.

       •   dump_peer_certificate

           allows you to get a plaintext description  of  the  certificate  the
           peer (usually the server) presented to us.

       •   ssl_read_all

           see ssl_write_all (below)

       •   ssl_write_all

           ssl_read_all()  and  ssl_write_all() provide true blocking semantics
           for these operations (see limitation, below, for explanation). These
           are much preferred to the low level API equivalents (which implement
           BSD blocking semantics). The message argument to ssl_write_all() can
           be a reference. This is helpful to avoid  unnecessary  copying  when
           writing something big, e.g:

               $data = 'A' x 1000000000;
               Net::SSLeay::ssl_write_all($ssl, \$data) or die "ssl write failed";

       •   ssl_read_CRLF

           uses  ssl_read_all()  to  read  in a line terminated with a carriage
           return followed by a linefeed (CRLF).  The CRLF is included  in  the
           returned scalar.

       •   ssl_read_until

           uses  ssl_read_all()  to  read  from  the  SSL input stream until it
           encounters a programmer specified delimiter.  If  the  delimiter  is
           undefined,  $/  is used.  If $/ is undefined, "\n" is used.  One can
           optionally set a maximum length of bytes to read from the SSL  input
           stream.

       •   ssl_write_CRLF

           writes $message and appends CRLF to the SSL output stream.

   Initialization
       In  order  to  use the low level API you should start your programs with
       the following incantation:

           use Net::SSLeay qw(die_now die_if_ssl_error);
           Net::SSLeay::load_error_strings();
           Net::SSLeay::SSLeay_add_ssl_algorithms();    # Important!
           Net::SSLeay::ENGINE_load_builtin_engines();  # If you want built-in engines
           Net::SSLeay::ENGINE_register_all_complete(); # If you want built-in engines
           Net::SSLeay::randomize();

   Error handling functions
       I can not emphasize the need  to  check  for  error  enough.  Use  these
       functions  even  in the most simple programs, they will reduce debugging
       time greatly. Do not ask questions on the mailing  list  without  having
       first sprinkled these in your code.

       •   die_now

       •   die_if_ssl_error

           die_now()  and die_if_ssl_error() are used to conveniently print the
           SSLeay error stack when something goes wrong:

               Net::SSLeay::connect($ssl) or die_now("Failed SSL connect ($!)");

               Net::SSLeay::write($ssl, "foo") or die_if_ssl_error("SSL write ($!)");

       •   print_errs

           You can also use Net::SSLeay::print_errs() to dump the  error  stack
           without  exiting the program. As can be seen, your code becomes much
           more readable if you import the error reporting functions into  your
           main name space.

   Sockets
       Perl  uses  file  handles for all I/O. While SSLeay has a quite flexible
       BIO mechanism and perl has an  evolved  PerlIO  mechanism,  this  module
       still  sticks  to  using  file  descriptors.  Thus to attach SSLeay to a
       socket  you  should  use  fileno()  to  extract  the   underlying   file
       descriptor:

           Net::SSLeay::set_fd($ssl, fileno(S));   # Must use fileno

       You  should  also set $| to 1 to eliminate STDIO buffering so you do not
       get confused if you use perl I/O functions  to  manipulate  your  socket
       handle.

       If  you  need  to select(2) on the socket, go right ahead, but be warned
       that OpenSSL does some internal buffering so SSL_read  does  not  always
       return  data  even  if  the  socket  selected  for reading (just keep on
       selecting and trying to read). "Net::SSLeay" is no different from the  C
       language OpenSSL in this respect.

   Callbacks
       You  can establish a per-context verify callback function something like
       this:

           sub verify {
               my ($ok, $x509_store_ctx) = @_;
               print "Verifying certificate...\n";
               # ...
               return $ok;
           }

       It is used like this:

           Net::SSLeay::set_verify ($ssl, Net::SSLeay::VERIFY_PEER, \&verify);

       Per-context callbacks for decrypting private keys are implemented.

           Net::SSLeay::CTX_set_default_passwd_cb($ctx, sub { "top-secret" });
           Net::SSLeay::CTX_use_PrivateKey_file($ctx, "key.pem",
                                                Net::SSLeay::FILETYPE_PEM)
               or die "Error reading private key";
           Net::SSLeay::CTX_set_default_passwd_cb($ctx, undef);

       If Hello Extensions are supported by  your  OpenSSL,  a  session  secret
       callback  can  be  set  up  to be called when a session secret is set by
       openssl.

       Establish it like this:

           Net::SSLeay::set_session_secret_cb($ssl, \&session_secret_cb, $somedata);

       It will be called like this:

           sub session_secret_cb {
               my ($secret, \@cipherlist, \$preferredcipher, $somedata) = @_;
           }

       No other callbacks are implemented. You do not need to use any  callback
       for  simple  (i.e.  normal)  cases  where  the  SSLeay  built-in  verify
       mechanism satisfies your needs.

       It is required to reset these callbacks to undef immediately  after  use
       to prevent memory leaks, thread safety problems and crashes on exit that
       can occur if different threads set different callbacks.

       If  you  want  to use callback stuff, see examples/callback.pl! It's the
       only one I am able to make work reliably.

   Low level API
       In addition to the high level  functions  outlined  above,  this  module
       contains  straight-forward  access  to CRYPTO and SSL parts of OpenSSL C
       API.

       See the "*.h" headers from OpenSSL C distribution  for  a  list  of  low
       level  SSLeay functions to call (check SSLeay.xs to see if some function
       has been implemented). The module strips the initial "SSL_" off  of  the
       SSLeay names.  Generally you should use "Net::SSLeay::" in its place.

       Note  that  some functions are prefixed with "P_" - these are very close
       to the original API however contain some kind of a  wrapper  making  its
       interface more perl friendly.

       For example:

       In C:

           #include <ssl.h>

           err = SSL_set_verify (ssl, SSL_VERIFY_CLIENT_ONCE, &your_call_back_here);

       In Perl:

           use Net::SSLeay;

           $err = Net::SSLeay::set_verify ($ssl,
                                           Net::SSLeay::VERIFY_CLIENT_ONCE,
                                           \&your_call_back_here);

       If  the  function  does  not  start  with "SSL_" you should use the full
       function name, e.g.:

           $err = Net::SSLeay::ERR_get_error;

       The following new functions behave in perlish way:

           $got = Net::SSLeay::read($ssl);
                                       # Performs SSL_read, but returns $got
                                       # resized according to data received.
                                       # Returns undef on failure.

           Net::SSLeay::write($ssl, $foo) || die;
                                       # Performs SSL_write, but automatically
                                       # figures out the size of $foo

       Low level API: Version and library information related functions

       •   OpenSSL_version_num and SSLeay

           COMPATIBILITY: SSLeay() is  not  available  in  Net-SSLeay-1.42  and
           before.  SSLeay()  was  made  an  alias  of OpenSSL_version_num() in
           OpenSSL 1.1.0 and LibreSSL 2.7.0.

           COMPATIBILITY:    OpenSSL_version_num()    requires     at     least
           Net-SSLeay-1.82 with OpenSSL 1.1.0, or Net-SSLeay-1.88 with LibreSSL
           2.7.0.

           Both  functions  return OPENSSL_VERSION_NUMBER constant (numeric) as
           defined by the underlying OpenSSL or LibreSSL library.

               my $ver_number = Net::SSLeay::SSLeay();
               # or
               my $ver_number = Net::SSLeay::OpenSSL_version_num();
               # returns: OPENSSL_VERSION_NUMBER constant

               # OpenSSL version numbering is:
               # 0x00903100 => openssl-0.9.3
               # 0x00904100 => openssl-0.9.4
               # 0x00905100 => openssl-0.9.5
               # 0x0090600f => openssl-0.9.6
               # 0x0090601f => openssl-0.9.6a
               # ...
               # 0x009060df => openssl-0.9.6m
               # 0x0090700f => openssl-0.9.7
               # 0x0090701f => openssl-0.9.7a
               # ...
               # 0x009070df => openssl-0.9.7m
               # 0x0090800f => openssl-0.9.8
               # 0x0090801f => openssl-0.9.8a
               # ...
               # 0x0090821f => openssl-0.9.8zh
               # 0x1000000f => openssl-1.0.0
               # ...
               # 0x1000014f => openssl-1.0.0t
               # 0x1000100f => openssl-1.0.1
               # ...
               # 0x1000115f => openssl-1.0.1u
               # 0x1000200f => openssl-1.0.2
               # ...
               # 0x1000215f => openssl-1.0.2u
               # 0x1010000f => openssl-1.1.0
               # ...
               # 0x101000cf => openssl-1.1.0l
               # 0x1010100f => openssl-1.1.1
               # ...
               # 0x1010117f => openssl-1.1.1w
               # 0x30000000 => openssl-3.0.0
               # ...
               # 0x300000c0 => openssl-3.0.12
               # 0x30100000 => openssl-3.1.0
               # ...
               # 0x30100040 => openssl-3.1.4
               # 0x30200000 => openssl-3.2.0

               # Note that OpenSSL 3.0.0 and later do not set the status nibble in the
               # least significant octet to f.

               # LibreSSL returns 0x20000000 always:
               # 0x20000000 => libressl-2.2.1
               # ...
               # 0x20000000 => libressl-3.8.2

           You can use the version number like this  when  you  know  that  the
           underlying library is OpenSSL:

               if (Net::SSLeay::SSLeay() < 0x0090800f) {
                   die "You need OpenSSL 0.9.8 or higher";
               }

           LibresSSL  2.2.2  and  later define constant LIBRESSL_VERSION_NUMBER
           that gives the LibreSSL version number. The format is the same  that
           OpenSSL  uses  with  OPENSSL_VERSION_NUMBER.  You can do this if you
           need to check that the  underlying  library  is  LibreSSL  and  it's
           recent enough:

               if (Net::SSLeay::SSLeay() != 0x20000000 ||
                       Net::SSLeay::LIBRESSL_VERSION_NUMBER() < 0x3040200f) {
                   die "You need LibreSSL. Version 3.4.2 or higher";
               }

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OpenSSL_version_num.html>

           See OpenSSL 1.1.1 and  earlier  documentation  for  the  details  of
           status nibble and the format interpretation.

       •   SSLeay_version

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

           Returns different strings depending on $type.

               my $ver_string = Net::SSLeay::SSLeay_version($type);
               # $type
               #   SSLEAY_VERSION  - e.g. 'OpenSSL 1.0.0d 8 Feb 2011'
               #   SSLEAY_CFLAGS   - e.g. 'compiler: gcc -D_WINDLL -DOPENSSL_USE_APPLINK .....'
               #   SSLEAY_BUILT_ON - e.g. 'built on: Fri May  6 00:00:46 GMT 2011'
               #   SSLEAY_PLATFORM - e.g. 'platform: mingw'
               #   SSLEAY_DIR      - e.g. 'OPENSSLDIR: "z:/...."'
               #
               # returns: string

               Net::SSLeay::SSLeay_version();
               # is equivalent to
               Net::SSLeay::SSLeay_version(SSLEAY_VERSION);

           OpenSSL    1.1.0   changed   SSLeay_version()   to   an   alias   of
           OpenSSL_version(). To ensure correct  functionality  with  LibreSSL,
           use SSLEAY_* constants with SSLeay_version() and OPENSSL_* constants
           with OpenSSL_version().

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OpenSSL_version.html>

           OpenSSL website no longer has a manual page for SSLeay_version().

       •   OpenSSL_version

           COMPATIBILITY: requires at least Net-SSLeay-1.82 with OpenSSL 1.1.0,
           or Net-SSLeay-1.88 with LibreSSL 2.7.0.

           Returns different strings depending on $t.  Available  $t  constants
           depend on the library version.

               my $ver_string = Net::SSLeay::OpenSSL_version($t);
               # $t
               #   OPENSSL_VERSION     - e.g. 'OpenSSL 1.1.0g  2 Nov 2017'
               #   OPENSSL_CFLAGS      - e.g. 'compiler: cc -DDSO_DLFCN -DHAVE_DLFCN_H .....'
               #   OPENSSL_BUILT_ON    - e.g. 'built on: reproducible build, date unspecified'
               #   OPENSSL_PLATFORM    - e.g. 'platform: darwin64-x86_64-cc'
               #   OPENSSL_DIR         - e.g. 'OPENSSLDIR: "/opt/openssl-1.1.0g"'
               #   OPENSSL_ENGINES_DIR - e.g. 'ENGINESDIR: "/opt/openssl-1.1.0g/lib/engines-1.1"'
               #
               # returns: string

               Net::SSLeay::OpenSSL_version();
               # is equivalent to
               Net::SSLeay::OpenSSL_version(OPENSSL_VERSION);

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OpenSSL_version.html>

       •   OPENSSL_info

           COMPATIBILITY: not available in Net-SSLeay-1.90 and before; requires
           at least OpenSSL 3.0.0-alpha1

           Returns different strings depending on $t.  Available  $t  constants
           depend on the library version.

               my $info_string = Net::SSLeay::OPENSSL_info($t);
               # $t
               #   OPENSSL_INFO_CONFIG_DIR - e.g. '/opt/openssl-3.0.1'
               #   OPENSSL_INFO_...
               #
               # returns: string

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OPENSSL_info.html>

       •   OPENSSL_version_major,           OPENSSL_version_minor           and
           OPENSSL_version_patch

           COMPATIBILITY: not available in Net-SSLeay-1.90 and before; requires
           at least OpenSSL 3.0.0-alpha1, not in LibreSSL

           Return  constants  OPENSSL_VERSION_MAJOR,  OPENSSL_VERSION_MINOR and
           OPENSSL_VERSION_PATCH, respectively.

               my $major = Net::SSLeay::OPENSSL_version_major();
               my $minor = Net::SSLeay::OPENSSL_version_minor();
               my $patch = Net::SSLeay::OPENSSL_version_patch();
               #
               # return: integer

           For example with OpenSSL 3.0.1, $major is 3, $minor is 0 and  $patch
           is 1.

           Note:  the  constants record Net::SSLeay compile time values whereas
           the three functions return values from the library. Typically  these
           are  the  same,  but they can be different if the library version is
           updated but Net::SSLeay is not  re-compiled.  See  the  OpenSSL  and
           LibreSSL API/ABI compatibility statements for more information.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OPENSSL_version_major.html>

       •   OPENSSL_version_pre_release

           COMPATIBILITY: not available in Net-SSLeay-1.90 and before; requires
           at least OpenSSL 3.0.0-alpha1, not in LibreSSL

           Return     constant     string     defined      by      C      macro
           OPENSSL_VERSION_PRE_RELEASE.

               my $pre_release = Net::SSLeay::OPENSSL_version_pre_release();
               #
               # returns: string (For example: "-alpha3" or "" for a release version)

           When the macro is not defined, an empty string is returned instead.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OPENSSL_version_pre_release.html>

       •   OPENSSL_version_build_metadata

           COMPATIBILITY: not available in Net-SSLeay-1.90 and before; requires
           at least OpenSSL 3.0.0-alpha1, not in LibreSSL

           Return     constant     string     defined      by      C      macro
           OPENSSL_VERSION_BUILD_METADATA.

               my $metadata = Net::SSLeay::OPENSSL_version_build_metadata();
               #
               # returns: string (For example: "+fips" or "")

           When the macro is not defined, an empty string is returned instead.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OPENSSL_version_build_metadata.html>

       Low level API: Initialization related functions

       •   library_init

           Initialize SSL library by registering algorithms.

               my $rv = Net::SSLeay::library_init();

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_library_init.html>

           While   the   original  function  from  OpenSSL  always  returns  1,
           Net::SSLeay adds a wrapper around it to make sure that  the  OpenSSL
           function  is  only  called once.  Thus the function will return 1 if
           initialization was done and 0 if not,  i.e.  if  initialization  was
           done already before.

       •   add_ssl_algorithms

           The alias for "library_init"

               Net::SSLeay::add_ssl_algorithms();

       •   OpenSSL_add_ssl_algorithms

           The alias for "library_init"

               Net::SSLeay::OpenSSL_add_ssl_algorithms();

       •   SSLeay_add_ssl_algorithms

           The alias for "library_init"

               Net::SSLeay::SSLeay_add_ssl_algorithms();

       •   load_error_strings

           Registers  the  error  strings  for  all  libcrypto + libssl related
           functions.

               Net::SSLeay::load_error_strings();
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/ERR_load_crypto_strings.html>

       •   ERR_load_crypto_strings

           Registers  the error strings for all libcrypto functions. No need to
           call this function if you have already called "load_error_strings".

               Net::SSLeay::ERR_load_crypto_strings();
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/ERR_load_crypto_strings.html>

       •   ERR_load_RAND_strings

           Registers  the  error strings for RAND related functions. No need to
           call this function if you have already called "load_error_strings".

               Net::SSLeay::ERR_load_RAND_strings();
               #
               # returns: no return value

       •   ERR_load_SSL_strings

           Registers the error strings for SSL related functions.  No  need  to
           call this function if you have already called "load_error_strings".

               Net::SSLeay::ERR_load_SSL_strings();
               #
               # returns: no return value

       •   OpenSSL_add_all_algorithms

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Add algorithms to internal table.

               Net::SSLeay::OpenSSL_add_all_algorithms();
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OpenSSL_add_all_algorithms.html>

       •   OPENSSL_add_all_algorithms_conf

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Similar to  "OpenSSL_add_all_algorithms"  -  will  ALWAYS  load  the
           config file

               Net::SSLeay::OPENSSL_add_all_algorithms_conf();
               #
               # returns: no return value

       •   OPENSSL_add_all_algorithms_noconf

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Similar to "OpenSSL_add_all_algorithms" - will NEVER load the config
           file

               Net::SSLeay::OPENSSL_add_all_algorithms_noconf();
               #
               # returns: no return value

       •   OPENSSL_cleanup

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.0-pre3 or LibreSSL 3.6.0

           Deinitialises OpenSSL libcrypto and libssl.

               Net::SSLeay::OPENSSL_cleanup();
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OPENSSL_cleanup>

       •   OPENSSL_init_crypto

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.0-pre3 not enabled for LibreSSL. LibreSSL  does
           not define "OPENSSL_INIT_SETTINGS".

           Initialises OpenSSL "libcrypto" with non-default settings.

               my $rv = Net::SSLeay::OPENSSL_init_crypto($opts, $settings);
               # $opts - (uin64_t) flags to be set (bitmask)
               # $settings - value corresponding to OPENSSL_INIT_SETTINGS structure or undef (optional)
               #
               # returns: 1 on success or 0 on error

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OPENSSL_init_crypto>

       •   OPENSSL_init_ssl

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.0-pre3 not enabled for LibreSSL. LibreSSL  does
           not define "OPENSSL_INIT_SETTINGS".

           Initialises OpenSSL "libssl" with non-default settings.

               my $rv = Net::SSLeay::OPENSSL_init_ssl($opts, $settings);
               # $opts - (uin64_t) flags to be set (bitmask)
               # $settings - value corresponding to OPENSSL_INIT_SETTINGS structure or undef (optional)
               #
               # returns: 1 on success or 0 on error

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OPENSSL_init_ssl>

       •   OPENSSL_INIT_new

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.0-pre3, not in LibreSSL

           Allocates an OpenSSL "OPENSSL_INIT_SETTINGS" object.

               my $settings = Net::SSLeay::OPENSSL_init_new()
               #
               # returns: value corresponding to OPENSSL_INIT_SETTINGS structure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/OPENSSL_INIT_new>

       •   OPENSSL_INIT_free

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.0-pre3, not in LibreSSL

           Releases  an  OpenSSL  "OPENSSL_INIT_SETTINGS" object allocated with
           "OPENSSL_INIT_new".

               Net::SSLeay::OPENSSL_init_free($settings)
               # $settings - value corresponding to OPENSSL_INIT_SETTINGS structure
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/OPENSSL_INIT_free>

       •   OPENSSL_INIT_set_config_filename

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.0-pre3, not in LibreSSL

           Specify a nondefault filename to load as OpenSSL configuration file.

               my $rv = Net::SSLeay::OPENSSL_INIT_set_config_filename($settings, $filename);
               # $settings - value corresponding to OPENSSL_INIT_SETTINGS structure
               # $filename - (string) filename
               #
               # returns: 1 on success or 0 on error

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OPENSSL_INIT_set_config_filename>

       •   OPENSSL_INIT_set_config_appname

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.0-pre3, not in LibreSSL

           Specify a nondefault application name.

               my $rv = Net::SSLeay::OPENSSL_INIT_set_config_appname($settings, $name);
               # $settings - value corresponding to OPENSSL_INIT_SETTINGS structure
               # $name - (string) application name
               #
               # returns: 1 on success or 0 on error

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/OPENSSL_INIT_set_config_appname>

       •   OPENSSL_INIT_set_config_file_flags

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 3.0.0-alpha1, not in LibreSSL

           Specify nondefault flags for loading OpenSSL configuration file.

               my $rv = Net::SSLeay::OPENSSL_INIT_set_config_file_flags($settings, $flags);
               # $settings - value corresponding to OPENSSL_INIT_SETTINGS structure
               # $flags - (unsigned long) flags to be set (bitmask)
               #
               # returns: 1 on success or 0 on error

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OPENSSL_INIT_set_config_file_flags>

       Low level API: ERR_* and SSL_alert_* related functions

       NOTE: Please note that SSL_alert_* function have  "SSL_"  part  stripped
       from their names.

       •   ERR_clear_error

           Clear the error queue.

               Net::SSLeay::ERR_clear_error();
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/ERR_clear_error.html>

       •   ERR_error_string

           Generates  a  human-readable  string  representing  the  error  code
           $error.

               my $rv = Net::SSLeay::ERR_error_string($error);
               # $error - (unsigned integer) error code
               #
               # returns: string

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/ERR_error_string.html>

       •   ERR_get_error

           Returns the earliest error code from the thread's  error  queue  and
           removes  the  entry.   This  function can be called repeatedly until
           there are no more error codes to return.

               my $rv = Net::SSLeay::ERR_get_error();
               #
               # returns: (unsigned integer) error code

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/ERR_get_error.html>

       •   ERR_peek_error

           Returns  the  earliest  error  code  from  the  thread's error queue
           without modifying it.

               my $rv = Net::SSLeay::ERR_peek_error();
               #
               # returns: (unsigned integer) error code

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/ERR_get_error.html>

       •   ERR_put_error

           Adds  an error code to the thread's error queue. It signals that the
           error of $reason code reason occurred in function $func  of  library
           $lib, in line number $line of $file.

               Net::SSLeay::ERR_put_error($lib, $func, $reason, $file, $line);
               # $lib - (integer) library id (check openssl/err.h for constants e.g. ERR_LIB_SSL)
               # $func - (integer) function id (check openssl/ssl.h for constants e.g. SSL_F_SSL23_READ)
               # $reason - (integer) reason id (check openssl/ssl.h for constants e.g. SSL_R_SSL_HANDSHAKE_FAILURE)
               # $file - (string) file name
               # $line - (integer) line number in $file
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/ERR_put_error.html> and
           <https://www.openssl.org/docs/manmaster/man3/err.html>

       •   alert_desc_string

           Returns a two letter string as a short form describing the reason of
           the alert specified by value.

               my $rv = Net::SSLeay::alert_desc_string($value);
               # $value - (integer) alert id (check openssl/ssl.h for SSL3_AD_* and TLS1_AD_* constants)
               #
               # returns: description string (2 letters)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_alert_type_string.html>

       •   alert_desc_string_long

           Returns  a  string  describing  the reason of the alert specified by
           value.

               my $rv = Net::SSLeay::alert_desc_string_long($value);
               # $value - (integer) alert id (check openssl/ssl.h for SSL3_AD_* and TLS1_AD_* constants)
               #
               # returns: description string

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_alert_type_string.html>

       •   alert_type_string

           Returns  a  one  letter  string  indicating  the  type  of the alert
           specified by value.

               my $rv = Net::SSLeay::alert_type_string($value);
               # $value - (integer) alert id (check openssl/ssl.h for SSL3_AD_* and TLS1_AD_* constants)
               #
               # returns: string (1 letter)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_alert_type_string.html>

       •   alert_type_string_long

           Returns  a  string  indicating  the  type  of the alert specified by
           value.

               my $rv = Net::SSLeay::alert_type_string_long($value);
               # $value - (integer) alert id (check openssl/ssl.h for SSL3_AD_* and TLS1_AD_* constants)
               #
               # returns: string

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_alert_type_string.html>

       Low level API: SSL_METHOD_* related functions

       •   SSLv23_method, SSLv23_server_method and SSLv23_client_method

           COMPATIBILITY: not available in Net-SSLeay-1.82 and before.

           Returns   SSL_METHOD   structure  corresponding  to  general-purpose
           version-flexible TLS method, the return value can be later used as a
           param of "CTX_new_with_method".

           NOTE:    Consider    using    TLS_method,    TLS_server_method    or
           TLS_client_method with new code.

               my $rv = Net::SSLeay::SSLv2_method();
               #
               # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

       •   SSLv2_method

           Returns  SSL_METHOD  structure  corresponding  to  SSLv2 method, the
           return value can be later used as a param of  "CTX_new_with_method".
           Only available where supported by the underlying openssl.

               my $rv = Net::SSLeay::SSLv2_method();
               #
               # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

       •   SSLv3_method

           Returns  SSL_METHOD  structure  corresponding  to  SSLv3 method, the
           return value can be later used as a param of "CTX_new_with_method".

               my $rv = Net::SSLeay::SSLv3_method();
               #
               # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_new.html>

       •   TLSv1_method, TLSv1_server_method and TLSv1_client_method

           COMPATIBILITY:  Requires  OpenSSL or LibreSSL built with support for
           TLSv1. Server and client methods not  available  in  Net-SSLeay-1.82
           and before.

           Returns  SSL_METHOD  structure  corresponding  to  TLSv1 method, the
           return value can be later used as a param of "CTX_new_with_method".

               my $rv = Net::SSLeay::TLSv1_method();
               #
               # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_new.html>

       •   TLSv1_1_method, TLSv1_1_server_method and TLSv1_1_client_method

           COMPATIBILITY:  Requires  OpenSSL  >=  1.0.1  or LibreSSL built with
           support for TLSv1.1. Server and  client  methods  not  available  in
           Net-SSLeay-1.82 and before.

           Returns  SSL_METHOD  structure  corresponding to TLSv1_1 method, the
           return value can be later used as a param of "CTX_new_with_method".

               my $rv = Net::SSLeay::TLSv1_1_method();
               #
               # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_new.html>

       •   TLSv1_2_method, TLSv1_2_server_method and TLSv1_2_client_method

           COMPATIBILITY:  Requires  OpenSSL  >=  1.0.1  or LibreSSL built with
           support for TLSv1.2. Server and  client  methods  not  available  in
           Net-SSLeay-1.82 and before.

           Returns  SSL_METHOD  structure  corresponding to TLSv1_2 method, the
           return value can be later used as a param of "CTX_new_with_method".

               my $rv = Net::SSLeay::TLSv1_2_method();
               #
               # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_new.html>

       •   TLS_method, TLS_server_method and TLS_client_method

           COMPATIBILITY: Not available in Net-SSLeay-1.82 and before.

           Returns   SSL_METHOD   structure  corresponding  to  general-purpose
           version-flexible TLS method, the return value can be later used as a
           param of "CTX_new_with_method". Only available  where  supported  by
           the underlying openssl.

               my $rv = Net::SSLeay::TLS_method();
               #
               # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_new.html>

       Low level API: ENGINE_* related functions

       •   ENGINE_load_builtin_engines

           COMPATIBILITY: Requires an OpenSSL build with dynamic engine loading
           support.

           Load all bundled ENGINEs into memory and make them visible.

               Net::SSLeay::ENGINE_load_builtin_engines();
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/ENGINE_by_id.html>

       •   ENGINE_register_all_complete

           COMPATIBILITY: Requires an OpenSSL build with dynamic engine loading
           support.

           Register  all  loaded  ENGINEs for every algorithm they collectively
           implement.

               Net::SSLeay::ENGINE_register_all_complete();
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/ENGINE_by_id.html>

       •   ENGINE_set_default

           COMPATIBILITY: Requires an OpenSSL build with dynamic engine loading
           support.

           Set default engine to $e + set its flags to $flags.

               my $rv = Net::SSLeay::ENGINE_set_default($e, $flags);
               # $e - value corresponding to openssl's ENGINE structure
               # $flags - (integer) engine flags
               #          flags value can be made by bitwise "OR"ing:
               #          0x0001 - ENGINE_METHOD_RSA
               #          0x0002 - ENGINE_METHOD_DSA
               #          0x0004 - ENGINE_METHOD_DH
               #          0x0008 - ENGINE_METHOD_RAND
               #          0x0010 - ENGINE_METHOD_ECDH
               #          0x0020 - ENGINE_METHOD_ECDSA
               #          0x0040 - ENGINE_METHOD_CIPHERS
               #          0x0080 - ENGINE_METHOD_DIGESTS
               #          0x0100 - ENGINE_METHOD_STORE
               #          0x0200 - ENGINE_METHOD_PKEY_METHS
               #          0x0400 - ENGINE_METHOD_PKEY_ASN1_METHS
               #          Obvious all-or-nothing cases:
               #          0xFFFF - ENGINE_METHOD_ALL
               #          0x0000 - ENGINE_METHOD_NONE
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/ENGINE_by_id.html>

       •   ENGINE_by_id

           Get ENGINE by its identification $id.

           COMPATIBILITY: Requires an OpenSSL build with dynamic engine loading
           support.

               my $rv = Net::SSLeay::ENGINE_by_id($id);
               # $id - (string) engine identification e.g. "dynamic"
               #
               # returns: value corresponding to openssl's ENGINE structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/ENGINE_by_id.html>

       Low level API: EVP_PKEY_* related functions

       •   EVP_PKEY_copy_parameters

           Copies the parameters from key $from to key $to.

               my $rv = Net::SSLeay::EVP_PKEY_copy_parameters($to, $from);
               # $to - value corresponding to openssl's EVP_PKEY structure
               # $from - value corresponding to openssl's EVP_PKEY structure
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/EVP_PKEY_cmp.html>

       •   EVP_PKEY_new

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Creates a new EVP_PKEY structure.

               my $rv = Net::SSLeay::EVP_PKEY_new();
               #
               # returns: value corresponding to openssl's EVP_PKEY structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/EVP_PKEY_new.html>

       •   EVP_PKEY_free

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Free an allocated EVP_PKEY structure.

               Net::SSLeay::EVP_PKEY_free($pkey);
               # $pkey - value corresponding to openssl's EVP_PKEY structure
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/EVP_PKEY_new.html>

       •   EVP_PKEY_assign_RSA

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Set the key referenced by $pkey to $key

           NOTE: No reference counter will be  increased,  i.e.  $key  will  be
           freed if $pkey is freed.

               my $rv = Net::SSLeay::EVP_PKEY_assign_RSA($pkey, $key);
               # $pkey - value corresponding to openssl's EVP_PKEY structure
               # $key - value corresponding to openssl's RSA structure
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/EVP_PKEY_assign_RSA.html>

       •   EVP_PKEY_assign_EC_KEY

           COMPATIBILITY: not available in Net-SSLeay-1.74 and before

           Set the key referenced by $pkey to $key

           NOTE: No reference counter will be  increased,  i.e.  $key  will  be
           freed if $pkey is freed.

               my $rv = Net::SSLeay::EVP_PKEY_assign_EC_KEY($pkey, $key);
               # $pkey - value corresponding to openssl's EVP_PKEY structure
               # $key - value corresponding to openssl's EC_KEY structure
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/EVP_PKEY_assign_EC_KEY.html>

       •   EVP_PKEY_bits

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns the size of the key $pkey in bits.

               my $rv = Net::SSLeay::EVP_PKEY_bits($pkey);
               # $pkey - value corresponding to openssl's EVP_PKEY structure
               #
               # returns: size in bits

       •   EVP_PKEY_security_bits

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at  least  OpenSSL  1.1.0   or   at   least   LibreSSL   3.6.0   and
           Net-SSLeay-1.94

           Returns the size of the key $pkey in bits.

               my $rv = Net::SSLeay::EVP_PKEY_security_bits($pkey);
               # $pkey - value corresponding to openssl's EVP_PKEY structure
               #
               # returns: number of bits

       •   EVP_PKEY_size

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns  the  maximum  size  of  a  signature  in  bytes. The actual
           signature may be smaller.

               my $rv = Net::SSLeay::EVP_PKEY_size($pkey);
               # $pkey - value corresponding to openssl's EVP_PKEY structure
               #
               # returns: the maximum size in bytes

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/EVP_PKEY_size.html>

       •   EVP_PKEY_id

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before; requires
           at least OpenSSL 1.0.0

           Returns $pkey type (integer value of corresponding NID).

               my $rv = Net::SSLeay::EVP_PKEY_id($pkey);
               # $pkey - value corresponding to openssl's EVP_PKEY structure
               #
               # returns: (integer) key type

           Example:

               my $pubkey = Net::SSLeay::X509_get_pubkey($x509);
               my $type = Net::SSLeay::EVP_PKEY_id($pubkey);
               print Net::SSLeay::OBJ_nid2sn($type);             # prints e.g. 'rsaEncryption'

       Low level API: PEM_* related functions

       Check openssl doc <https://www.openssl.org/docs/manmaster/man3/pem.html>

       •   PEM_read_bio_X509

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Loads PEM formatted X509 certificate via given BIO structure.

               my $rv = Net::SSLeay::PEM_read_bio_X509($bio);
               # $bio - value corresponding to openssl's BIO structure
               #
               # returns: value corresponding to openssl's X509 structure (0 on failure)

           Example:

               my $bio = Net::SSLeay::BIO_new_file($filename, 'r');
               my $x509 = Net::SSLeay::PEM_read_bio_X509($bio);
               Net::SSLeay::BIO_free($bio);

       •   PEM_read_bio_X509_REQ

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Loads PEM formatted X509_REQ object via given BIO structure.

               my $rv = Net::SSLeay::PEM_read_bio_X509_REQ($bio, $x=NULL, $cb=NULL, $u=NULL);
               # $bio - value corresponding to openssl's BIO structure
               #
               # returns: value corresponding to openssl's X509_REQ structure (0 on failure)

           Example:

               my $bio = Net::SSLeay::BIO_new_file($filename, 'r');
               my $x509_req = Net::SSLeay::PEM_read_bio_X509_REQ($bio);
               Net::SSLeay::BIO_free($bio);

       •   PEM_read_bio_DHparams

           Reads DH structure from BIO.

               my $rv = Net::SSLeay::PEM_read_bio_DHparams($bio);
               # $bio - value corresponding to openssl's BIO structure
               #
               # returns: value corresponding to openssl's DH structure (0 on failure)

       •   PEM_read_bio_X509_CRL

           Reads X509_CRL structure from BIO.

               my $rv = Net::SSLeay::PEM_read_bio_X509_CRL($bio);
               # $bio - value corresponding to openssl's BIO structure
               #
               # returns: value corresponding to openssl's X509_CRL structure (0 on failure)

       •   PEM_read_bio_PrivateKey

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Loads PEM formatted private key via given BIO structure.

               my $rv = Net::SSLeay::PEM_read_bio_PrivateKey($bio, $cb, $data);
               # $bio - value corresponding to openssl's BIO structure
               # $cb - reference to perl callback function
               # $data - data that will be passed to callback function (see examples below)
               #
               # returns: value corresponding to openssl's EVP_PKEY structure (0 on failure)

           Example:

               my $bio = Net::SSLeay::BIO_new_file($filename, 'r');
               my $privkey = Net::SSLeay::PEM_read_bio_PrivateKey($bio); # ask for password if needed
               Net::SSLeay::BIO_free($bio);

           To use password you have the following options:

               $privkey = Net::SSLeay::PEM_read_bio_PrivateKey($bio, \&callback_func); # use callback func for getting password
               $privkey = Net::SSLeay::PEM_read_bio_PrivateKey($bio, \&callback_func, $data); # use callback_func + pass $data to callback_func
               $privkey = Net::SSLeay::PEM_read_bio_PrivateKey($bio, undef, "secret"); # use password "secret"
               $privkey = Net::SSLeay::PEM_read_bio_PrivateKey($bio, undef, "");       # use empty password

           Callback function signature:

               sub callback_func {
                   my ($max_passwd_size, $rwflag, $data) = @_;
                   # $max_passwd_size - maximum size of returned password (longer values will be discarded)
                   # $rwflag - indicates whether we are loading (0) or storing (1) - for PEM_read_bio_PrivateKey always 0
                   # $data - the data passed to PEM_read_bio_PrivateKey as 3rd parameter

                   return "secret";
               }

       •   PEM_X509_INFO_read_bio

           Reads   a   BIO   containing   a   PEM   formatted   file   into   a
           STACK_OF(X509_INFO) structure.

               my $rv = Net::SSLeay::PEM_X509_INFO_read_bio($bio);
               # $bio - value corresponding to openssl's BIO structure
               #
               # returns: value corresponding to openssl's STACK_OF(X509_INFO) structure.

           Example:

               my $bio = Net::SSLeay::BIO_new_file($filename, 'r');
               my $sk_x509_info = Net::SSLeay::PEM_X509_INFO_read_bio($bio);
               Net::SSLeay::BIO_free($bio);

       •   PEM_get_string_X509

           NOTE: Does not exactly correspond to any low level API function

           Converts/exports X509 certificate to string (PEM format).

               Net::SSLeay::PEM_get_string_X509($x509);
               # $x509 - value corresponding to openssl's X509 structure
               #
               # returns: string with $x509 in PEM format

       •   PEM_get_string_PrivateKey

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before. Requires
           legacy provider with OpenSSL 3.0 and later if the default  value  of
           $enc_alg ("DES_CBC") is used.

           Converts  public  key  $pk  into  PEM  formatted  string (optionally
           protected with password).

               my $rv = Net::SSLeay::PEM_get_string_PrivateKey($pk, $passwd, $enc_alg);
               # $pk - value corresponding to openssl's EVP_PKEY structure
               # $passwd - [optional] (string) password to use for key encryption
               # $enc_alg - [optional] algorithm to use for key encryption (default: DES_CBC) - value corresponding to openssl's EVP_CIPHER structure
               #
               # returns: PEM formatted string

           Examples:

               $pem_privkey = Net::SSLeay::PEM_get_string_PrivateKey($pk);
               $pem_privkey = Net::SSLeay::PEM_get_string_PrivateKey($pk, "secret");
               $pem_privkey = Net::SSLeay::PEM_get_string_PrivateKey($pk, "secret", Net::SSLeay::EVP_get_cipherbyname("DES-EDE3-CBC"));

       •   PEM_get_string_X509_CRL

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Converts X509_CRL object $x509_crl into PEM formatted string.

               Net::SSLeay::PEM_get_string_X509_CRL($x509_crl);
               # $x509_crl - value corresponding to openssl's X509_CRL structure
               #
               # returns: no return value

       •   PEM_get_string_X509_REQ

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Converts X509_REQ object $x509_crl into PEM formatted string.

               Net::SSLeay::PEM_get_string_X509_REQ($x509_req);
               # $x509_req - value corresponding to openssl's X509_REQ structure
               #
               # returns: no return value

       Low level API: d2i_* (DER format) related functions

       •   d2i_X509_bio

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Loads DER formatted X509 certificate via given BIO structure.

               my $rv = Net::SSLeay::d2i_X509_bio($bp);
               # $bp - value corresponding to openssl's BIO structure
               #
               # returns: value corresponding to openssl's X509 structure (0 on failure)

           Example:

               my $bio = Net::SSLeay::BIO_new_file($filename, 'rb');
               my $x509 = Net::SSLeay::d2i_X509_bio($bio);
               Net::SSLeay::BIO_free($bio);

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/d2i_X509.html>

       •   d2i_X509_CRL_bio

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Loads DER formatted X509_CRL object via given BIO structure.

               my $rv = Net::SSLeay::d2i_X509_CRL_bio($bp);
               # $bp - value corresponding to openssl's BIO structure
               #
               # returns: value corresponding to openssl's X509_CRL structure (0 on failure)

           Example:

               my $bio = Net::SSLeay::BIO_new_file($filename, 'rb');
               my $x509_crl = Net::SSLeay::d2i_X509_CRL_bio($bio);
               Net::SSLeay::BIO_free($bio);

       •   d2i_X509_REQ_bio

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Loads DER formatted X509_REQ object via given BIO structure.

               my $rv = Net::SSLeay::d2i_X509_REQ_bio($bp);
               # $bp - value corresponding to openssl's BIO structure
               #
               # returns: value corresponding to openssl's X509_REQ structure (0 on failure)

           Example:

               my $bio = Net::SSLeay::BIO_new_file($filename, 'rb');
               my $x509_req = Net::SSLeay::d2i_X509_REQ_bio($bio);
               Net::SSLeay::BIO_free($bio);

       Low level API: PKCS12 related functions

       •   P_PKCS12_load_file

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Loads  X509 certificate + private key + certificates of CA chain (if
           present in PKCS12 file).

               my ($privkey, $cert, @cachain) = Net::SSLeay::P_PKCS12_load_file($filename, $load_chain, $password);
               # $filename - name of PKCS12 file
               # $load_chain - [optional] whether load (1) or not(0) CA chain (default: 0)
               # $password - [optional] password for private key
               #
               # returns: triplet ($privkey, $cert, @cachain)
               #          $privkey - value corresponding to openssl's EVP_PKEY structure
               #          $cert - value corresponding to openssl's X509 structure
               #          @cachain - array of values corresponding to openssl's X509 structure (empty if no CA chain in PKCS12)

           IMPORTANT NOTE: after you do the job you need to call X509_free() on
           $privkey + all members of @cachain and EVP_PKEY_free() on $privkey.

           Examples:

               my ($privkey, $cert) = Net::SSLeay::P_PKCS12_load_file($filename);
               # or
               my ($privkey, $cert) = Net::SSLeay::P_PKCS12_load_file($filename, 0, $password);
               # or
               my ($privkey, $cert, @cachain) = Net::SSLeay::P_PKCS12_load_file($filename, 1);
               # or
               my ($privkey, $cert, @cachain) = Net::SSLeay::P_PKCS12_load_file($filename, 1, $password);

               # BEWARE: THIS IS WRONG - MEMORY LEAKS! (you cannot free @cachain items)
               my ($privkey, $cert) = Net::SSLeay::P_PKCS12_load_file($filename, 1, $password);

           NOTE Net::SSLeay 1.92_01 and  earlier:  With  some  combinations  of
           Windows,  perl, compiler and compiler options, you may see a runtime
           error        "no        OPENSSL_Applink",        when        calling
           Net::SSLeay::P_PKCS12_load_file. See README.Win32 for more details.

       Low level API: SESSION_* related functions

       •   d2i_SSL_SESSION

           COMPATIBILITY: does not work in Net-SSLeay-1.85 and before

           Transforms  the  binary  ASN1  representation  string  of an SSL/TLS
           session into an SSL_SESSION object.

               my $ses = Net::SSLeay::d2i_SSL_SESSION($data);
               # $data - the session as ASN1 representation string
               #
               # returns: $ses - the new SSL_SESSION

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/i2d_SSL_SESSION.html>

       •   i2d_SSL_SESSION

           COMPATIBILITY: does not work in Net-SSLeay-1.85 and before

           Transforms  the  SSL_SESSION  object in into the ASN1 representation
           and returns it as string.

               my $data = Net::SSLeay::i2d_SSL_SESSION($ses);
               # $ses - value corresponding to openssl's SSL_SESSION structure
               #
               # returns: $data - session as string

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/d2i_SSL_SESSION.html>

       •   SESSION_new

           Creates a new SSL_SESSION structure.

               my $rv = Net::SSLeay::SESSION_new();
               #
               # returns: value corresponding to openssl's SSL_SESSION structure (0 on failure)

       •   SESSION_free

           Free an allocated SSL_SESSION structure.

               Net::SSLeay::SESSION_free($ses);
               # $ses - value corresponding to openssl's SSL_SESSION structure
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_SESSION_free.html>

       •   SESSION_up_ref

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at least OpenSSL 1.1.0-pre4 or LibreSSL 2.7.0

           Increases the reference counter on a SSL_SESSION structure.

               Net::SSLeay::SESSION_up_ref($ses);
               # $ses - value corresponding to openssl's SSL_SESSION structure
               #
               # returns: 1 on success else 0

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_SESSION_up_ref.html>

       •   SESSION_dup

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at least OpenSSL 1.1.1, not in LibreSSL

           Duplicates a SSL_SESSION structure.

               Net::SSLeay::SESSION_dup($ses);
               # $ses - value corresponding to openssl's SSL_SESSION structure
               #
               # returns: the duplicated session

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_SESSION_dup.html>

       •   SESSION_is_resumable

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at least OpenSSL 1.1.1, not in LibreSSL

           Determine whether an SSL_SESSION object can be used for resumption.

               Net::SSLeay::SESSION_is_resumable($ses);
               # $ses - value corresponding to openssl's SSL_SESSION structure
               #
               # returns: (integer) 1 if it can or 0 if not

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_SESSION_is_resumable.html>

       •   SESSION_cmp

           Compare two SSL_SESSION structures.

               my $rv = Net::SSLeay::SESSION_cmp($sesa, $sesb);
               # $sesa - value corresponding to openssl's SSL_SESSION structure
               # $sesb - value corresponding to openssl's SSL_SESSION structure
               #
               # returns: 0 if the two structures are the same

           NOTE: Not available in openssl 1.0 or later

       •   SESSION_get_app_data

           Can be used to get application defined value/data.

               my $rv = Net::SSLeay::SESSION_get_app_data($ses);
               # $ses - value corresponding to openssl's SSL_SESSION structure
               #
               # returns: string/buffer/pointer ???

       •   SESSION_set_app_data

           Can be used to set some application defined value/data.

               my $rv = Net::SSLeay::SESSION_set_app_data($s, $a);
               # $s - value corresponding to openssl's SSL_SESSION structure
               # $a - (string/buffer/pointer ???) data
               #
               # returns: ???

       •   SESSION_get_ex_data

           Is used to retrieve the information for $idx from session $ses.

               my $rv = Net::SSLeay::SESSION_get_ex_data($ses, $idx);
               # $ses - value corresponding to openssl's SSL_SESSION structure
               # $idx - (integer) index for application specific data
               #
               # returns: pointer to ???

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_SESSION_get_ex_new_index.html>

       •   SESSION_set_ex_data

           Is used to store application data at arg for idx  into  the  session
           object.

               my $rv = Net::SSLeay::SESSION_set_ex_data($ss, $idx, $data);
               # $ss - value corresponding to openssl's SSL_SESSION structure
               # $idx - (integer) ???
               # $data - (pointer) ???
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_SESSION_get_ex_new_index.html>

       •   SESSION_get_ex_new_index

           Is used to register a new index for application specific data.

               my $rv = Net::SSLeay::SESSION_get_ex_new_index($argl, $argp, $new_func, $dup_func, $free_func);
               # $argl - (long) ???
               # $argp - (pointer) ???
               # $new_func - function pointer ??? (CRYPTO_EX_new *)
               # $dup_func - function pointer ??? (CRYPTO_EX_dup *)
               # $free_func - function pointer ??? (CRYPTO_EX_free *)
               #
               # returns: (integer) ???

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_SESSION_get_ex_new_index.html>

       •   SESSION_get_master_key

           NOTE: Does not exactly correspond to any low level API function

           Returns 'master_key' value from SSL_SESSION structure $s

               Net::SSLeay::SESSION_get_master_key($s);
               # $s - value corresponding to openssl's SSL_SESSION structure
               #
               # returns: master key (binary data)

       •   SESSION_set1_master_key

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.1pre1, not in LibreSSL

           Sets the master key value associated with a SSL_SESSION.

               my $ret = Net::SSLeay::SESSION_set1_master_key($sess, $key);
               # $sess - value corresponding to OpenSSL SSL_SESSION structure
               # $key - PSK key in packed binary format
               #
               # returns: 1 on success, 0 on failure

           Example:

               my $key = pack('H*', 'deadbeef');
               my $ret = Net::SSLeay::SESSION_set1_master_key($sess, $key);

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_SESSION_set1_master_key.html>

       •   SESSION_set_master_key

           Sets 'master_key' value for SSL_SESSION structure $s

               Net::SSLeay::SESSION_set_master_key($s, $key);
               # $s - value corresponding to openssl's SSL_SESSION structure
               # $key - master key (binary data)
               #
               # returns: no return value

           Not available with OpenSSL 1.1 and later.  Code that previously used
           SESSION_set_master_key must now set $secret  in  the  session_secret
           callback set with SSL_set_session_secret_cb.

       •   SESSION_set_cipher

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.1pre1, not in LibreSSL

           Set the ciphersuite associated with an SSL_SESSION.

               my $ret = Net::SSLeay::SESSION_set_cipher($s, $cipher);
               # $s - value corresponding to OpenSSL SSL_SESSION structure
               # $cipher - value corresponding to OpenSSL SSL_CIPHER structure
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_SESSION_set_cipher.html>

       •   SESSION_set_protocol_version

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.1pre1, not in LibreSSL

           Sets the protocol version associated with an SSL_SESSION.

               my $ret = Net::SSLeay::SESSION_set_protocol_version($s, $version);
               # $s - value corresponding to OpenSSL SSL_SESSION structure
               # $version - integer version constant. For example Net::SSLeay::TLS1_3_VERSION()
               #
               # returns: 1 on success, 0 on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_SESSION_set_protocol_version.html>

       •   SESSION_get0_cipher

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.0 or LibreSSL 3.4.0

           Returns  the  value corresponding to OpenSSL's SSL_CIPHER associated
           with an SSL_SESSION.

               my $ret = Net::SSLeay::SESSION_get0_cipher($s);
               # $s - value corresponding to OpenSSL SSL_SESSION structure
               #
               # returns: A value corresponding to OpenSSL's SSL_CIPHER structure or undef if SSL_CIPHER can't be determined.

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_SESSION_get0_cipher.html>

       •   SESSION_get_time

           Returns  the  time at which the session s was established.  The time
           is given in seconds since 1.1.1970.

               my $rv = Net::SSLeay::SESSION_get_time($s);
               # $s - value corresponding to openssl's SSL_SESSION structure
               #
               # returns: timestamp (seconds since 1.1.1970)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_SESSION_get_time.html>

       •   get_time

           Technically the same functionality as "SESSION_get_time".

               my $rv = Net::SSLeay::get_time($s);

       •   SESSION_get_timeout

           Returns the timeout value set for session $s in seconds.

               my $rv = Net::SSLeay::SESSION_get_timeout($s);
               # $s - value corresponding to openssl's SSL_SESSION structure
               #
               # returns: timeout (in seconds)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_SESSION_get_time.html>

       •   get_timeout

           Technically the same functionality as "SESSION_get_timeout".

               my $rv = Net::SSLeay::get_timeout($s);

       •   SESSION_print

           NOTE: Does not exactly correspond to any low level API function

           Prints session details (e.g. protocol  version,  cipher,  session-id
           ...) to BIO.

               my $rv = Net::SSLeay::SESSION_print($fp, $ses);
               # $fp - value corresponding to openssl's BIO structure
               # $ses - value corresponding to openssl's SSL_SESSION structure
               #
               # returns: 1 on success, 0 on failure

           You have to use necessary BIO functions like this:

               # let us have $ssl corresponding to openssl's SSL structure
               my $ses = Net::SSLeay::get_session($ssl);
               my $bio = Net::SSLeay::BIO_new(&Net::SSLeay::BIO_s_mem);
               Net::SSLeay::SESSION_print($bio, $ses);
               print Net::SSLeay::BIO_read($bio);

       •   SESSION_print_fp

           Prints  session  details  (e.g. protocol version, cipher, session-id
           ...) to file handle.

           NOTE With some combinations of Windows, perl, compiler and  compiler
           options,  you  may  see  a  runtime error "no OPENSSL_Applink", when
           calling Net::SSLeay::SESSION_print_fp.  See  README.Win32  for  more
           details.

               my $rv = Net::SSLeay::SESSION_print_fp($fp, $ses);
               # $fp - perl file handle
               # $ses - value corresponding to openssl's SSL_SESSION structure
               #
               # returns: 1 on success, 0 on failure

           Example:

               # let us have $ssl corresponding to openssl's SSL structure
               my $ses = Net::SSLeay::get_session($ssl);
               open my $fh, ">", "output.txt";
               Net::SSLeay::SESSION_print_fp($fh,$ses);

           Similar functionality without Net::SSLeay::SESSION_print_fp

               my $ses = Net::SSLeay::get_session($ssl);
               my $bio = Net::SSLeay::BIO_new_file('output.txt', 'w');
               Net::SSLeay::SESSION_print($bio, $ses);

       •   SESSION_set_time

           Replaces the creation time of the session s with the chosen value $t
           (seconds since 1.1.1970).

               my $rv = Net::SSLeay::SESSION_set_time($ses, $t);
               # $ses - value corresponding to openssl's SSL_SESSION structure
               # $t - time value
               #
               # returns: 1 on success

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_SESSION_get_time.html>

       •   set_time

           Technically the same functionality as "SESSION_set_time".

               my $rv = Net::SSLeay::set_time($ses, $t);

       •   SESSION_set_timeout

           Sets the timeout value for session s in seconds to $t.

               my $rv = Net::SSLeay::SESSION_set_timeout($s, $t);
               # $s - value corresponding to openssl's SSL_SESSION structure
               # $t - timeout (in seconds)
               #
               # returns: 1 on success

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_SESSION_get_time.html>

       •   set_timeout

           Technically the same functionality as "SESSION_set_timeout".

               my $rv = Net::SSLeay::set_timeout($ses, $t);

       Low level API: SSL_CTX_* related functions

       NOTE:  Please  note  that  the  function  described in this chapter have
       "SSL_" part stripped from their original openssl names.

       •   CTX_add_client_CA

           Adds the CA name extracted from $cacert to the list of CAs  sent  to
           the client when requesting a client certificate for $ctx.

               my $rv = Net::SSLeay::CTX_add_client_CA($ctx, $cacert);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $cacert - value corresponding to openssl's X509 structure
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_client_CA_list.html>

       •   CTX_add_extra_chain_cert

           Adds the  certificate  $x509  to  the  certificate  chain  presented
           together with the certificate. Several certificates can be added one
           after the other.

               my $rv = Net::SSLeay::CTX_add_extra_chain_cert($ctx, $x509);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $x509 - value corresponding to openssl's X509 structure
               #
               # returns: 1 on success, check out the error stack to find out the reason for failure otherwise

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_add_extra_chain_cert.html>

       •   CTX_add_session

           Adds the session $ses to the context $ctx.

               my $rv = Net::SSLeay::CTX_add_session($ctx, $ses);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $ses - value corresponding to openssl's SSL_SESSION structure
               #
               # returns: 1 on success, 0 on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_add_session.html>

       •   CTX_callback_ctrl

           ??? (more info needed)

               my $rv = Net::SSLeay::CTX_callback_ctrl($ctx, $cmd, $fp);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $cmd - (integer) command id
               # $fp - (function pointer) ???
               #
               # returns: ???

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_ctrl.html>

       •   CTX_check_private_key

           Checks the consistency of  a  private  key  with  the  corresponding
           certificate loaded into $ctx.

               my $rv = Net::SSLeay::CTX_check_private_key($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   CTX_ctrl

           Internal handling function for SSL_CTX objects.

           BEWARE: openssl doc says:  This  function  should  never  be  called
           directly!

               my $rv = Net::SSLeay::CTX_ctrl($ctx, $cmd, $larg, $parg);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $cmd - (integer) command id
               # $larg - (integer) long ???
               # $parg - (string/pointer) ???
               #
               # returns: (long) result of given command ???

               # valid $cmd values
               # 1 - SSL_CTRL_NEED_TMP_RSA
               # 2 - SSL_CTRL_SET_TMP_RSA
               # 3 - SSL_CTRL_SET_TMP_DH
               # 4 - SSL_CTRL_SET_TMP_ECDH
               # 5 - SSL_CTRL_SET_TMP_RSA_CB
               # 6 - SSL_CTRL_SET_TMP_DH_CB
               # 7 - SSL_CTRL_SET_TMP_ECDH_CB
               # 8 - SSL_CTRL_GET_SESSION_REUSED
               # 9 - SSL_CTRL_GET_CLIENT_CERT_REQUEST
               # 10 - SSL_CTRL_GET_NUM_RENEGOTIATIONS
               # 11 - SSL_CTRL_CLEAR_NUM_RENEGOTIATIONS
               # 12 - SSL_CTRL_GET_TOTAL_RENEGOTIATIONS
               # 13 - SSL_CTRL_GET_FLAGS
               # 14 - SSL_CTRL_EXTRA_CHAIN_CERT
               # 15 - SSL_CTRL_SET_MSG_CALLBACK
               # 16 - SSL_CTRL_SET_MSG_CALLBACK_ARG
               # 17 - SSL_CTRL_SET_MTU
               # 20 - SSL_CTRL_SESS_NUMBER
               # 21 - SSL_CTRL_SESS_CONNECT
               # 22 - SSL_CTRL_SESS_CONNECT_GOOD
               # 23 - SSL_CTRL_SESS_CONNECT_RENEGOTIATE
               # 24 - SSL_CTRL_SESS_ACCEPT
               # 25 - SSL_CTRL_SESS_ACCEPT_GOOD
               # 26 - SSL_CTRL_SESS_ACCEPT_RENEGOTIATE
               # 27 - SSL_CTRL_SESS_HIT
               # 28 - SSL_CTRL_SESS_CB_HIT
               # 29 - SSL_CTRL_SESS_MISSES
               # 30 - SSL_CTRL_SESS_TIMEOUTS
               # 31 - SSL_CTRL_SESS_CACHE_FULL
               # 32 - SSL_CTRL_OPTIONS
               # 33 - SSL_CTRL_MODE
               # 40 - SSL_CTRL_GET_READ_AHEAD
               # 41 - SSL_CTRL_SET_READ_AHEAD
               # 42 - SSL_CTRL_SET_SESS_CACHE_SIZE
               # 43 - SSL_CTRL_GET_SESS_CACHE_SIZE
               # 44 - SSL_CTRL_SET_SESS_CACHE_MODE
               # 45 - SSL_CTRL_GET_SESS_CACHE_MODE
               # 50 - SSL_CTRL_GET_MAX_CERT_LIST
               # 51 - SSL_CTRL_SET_MAX_CERT_LIST
               # 52 - SSL_CTRL_SET_MAX_SEND_FRAGMENT
               # 53 - SSL_CTRL_SET_TLSEXT_SERVERNAME_CB
               # 54 - SSL_CTRL_SET_TLSEXT_SERVERNAME_ARG
               # 55 - SSL_CTRL_SET_TLSEXT_HOSTNAME
               # 56 - SSL_CTRL_SET_TLSEXT_DEBUG_CB
               # 57 - SSL_CTRL_SET_TLSEXT_DEBUG_ARG
               # 58 - SSL_CTRL_GET_TLSEXT_TICKET_KEYS
               # 59 - SSL_CTRL_SET_TLSEXT_TICKET_KEYS
               # 60 - SSL_CTRL_SET_TLSEXT_OPAQUE_PRF_INPUT
               # 61 - SSL_CTRL_SET_TLSEXT_OPAQUE_PRF_INPUT_CB
               # 62 - SSL_CTRL_SET_TLSEXT_OPAQUE_PRF_INPUT_CB_ARG
               # 63 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_CB
               # 64 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_CB_ARG
               # 65 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_TYPE
               # 66 - SSL_CTRL_GET_TLSEXT_STATUS_REQ_EXTS
               # 67 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_EXTS
               # 68 - SSL_CTRL_GET_TLSEXT_STATUS_REQ_IDS
               # 69 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_IDS
               # 70 - SSL_CTRL_GET_TLSEXT_STATUS_REQ_OCSP_RESP
               # 71 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_OCSP_RESP
               # 72 - SSL_CTRL_SET_TLSEXT_TICKET_KEY_CB
               # 73 - DTLS_CTRL_GET_TIMEOUT
               # 74 - DTLS_CTRL_HANDLE_TIMEOUT
               # 75 - DTLS_CTRL_LISTEN
               # 76 - SSL_CTRL_GET_RI_SUPPORT
               # 77 - SSL_CTRL_CLEAR_OPTIONS
               # 78 - SSL_CTRL_CLEAR_MODE

               # 82 - SSL_CTRL_GET_EXTRA_CHAIN_CERTS
               # 83 - SSL_CTRL_CLEAR_EXTRA_CHAIN_CERTS

               # 88 - SSL_CTRL_CHAIN
               # 89 - SSL_CTRL_CHAIN_CERT

               # 90 - SSL_CTRL_GET_CURVES
               # 91 - SSL_CTRL_SET_CURVES
               # 92 - SSL_CTRL_SET_CURVES_LIST
               # 93 - SSL_CTRL_GET_SHARED_CURVE
               # 94 - SSL_CTRL_SET_ECDH_AUTO
               # 97 - SSL_CTRL_SET_SIGALGS
               # 98 - SSL_CTRL_SET_SIGALGS_LIST
               # 99 - SSL_CTRL_CERT_FLAGS
               # 100 - SSL_CTRL_CLEAR_CERT_FLAGS
               # 101 - SSL_CTRL_SET_CLIENT_SIGALGS
               # 102 - SSL_CTRL_SET_CLIENT_SIGALGS_LIST
               # 103 - SSL_CTRL_GET_CLIENT_CERT_TYPES
               # 104 - SSL_CTRL_SET_CLIENT_CERT_TYPES
               # 105 - SSL_CTRL_BUILD_CERT_CHAIN
               # 106 - SSL_CTRL_SET_VERIFY_CERT_STORE
               # 107 - SSL_CTRL_SET_CHAIN_CERT_STORE
               # 108 - SSL_CTRL_GET_PEER_SIGNATURE_NID
               # 109 - SSL_CTRL_GET_SERVER_TMP_KEY
               # 110 - SSL_CTRL_GET_RAW_CIPHERLIST
               # 111 - SSL_CTRL_GET_EC_POINT_FORMATS
               # 112 - SSL_CTRL_GET_TLSA_RECORD
               # 113 - SSL_CTRL_SET_TLSA_RECORD
               # 114 - SSL_CTRL_PULL_TLSA_RECORD

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_ctrl.html>

       •   CTX_flush_sessions

           Causes a run through the session cache of $ctx  to  remove  sessions
           expired at time $tm.

               Net::SSLeay::CTX_flush_sessions($ctx, $tm);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $tm - specifies the time which should be used for the expiration test (seconds since 1.1.1970)
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_flush_sessions.html>

       •   CTX_free

           Free an allocated SSL_CTX object.

               Net::SSLeay::CTX_free($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_free.html>

       •   CTX_get_app_data

           Can be used to get application defined value/data.

               my $rv = Net::SSLeay::CTX_get_app_data($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: string/buffer/pointer ???

       •   CTX_set_app_data

           Can be used to set some application defined value/data.

               my $rv = Net::SSLeay::CTX_set_app_data($ctx, $arg);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $arg - (string/buffer/pointer ???) data
               #
               # returns: ???

       •   CTX_get0_param

           COMPATIBILITY: not available in Net-SSLeay-1.82 and before; requires
           at least OpenSSL 1.0.2-beta1 or LibreSSL 2.7.0

           Returns the current verification parameters.

               my $vpm = Net::SSLeay::CTX_get0_param($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: value corresponding to openssl's X509_VERIFY_PARAM structure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get0_param.html>

       •   CTX_get_cert_store

           Returns the current certificate verification storage.

               my $rv = Net::SSLeay::CTX_get_cert_store($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: value corresponding to openssl's X509_STORE structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_cert_store.html>

       •   CTX_get_client_CA_list

           Returns  the  list  of  client  CAs  explicitly  set  for $ctx using
           "CTX_set_client_CA_list".

               my $rv = Net::SSLeay::CTX_get_client_CA_list($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: value corresponding to openssl's X509_NAME_STACK structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_client_CA_list.html>

       •   CTX_get_ex_data

           Is used to retrieve the information for index $idx from $ctx.

               my $rv = Net::SSLeay::CTX_get_ex_data($ssl, $idx);
               # $ssl - value corresponding to openssl's SSL_CTX structure
               # $idx - (integer) index for application specific data
               #
               # returns: pointer to ???

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_ex_new_index.html>

       •   CTX_get_ex_new_index

           Is used to register a new index for application specific data.

               my $rv = Net::SSLeay::CTX_get_ex_new_index($argl, $argp, $new_func, $dup_func, $free_func);
               # $argl - (long) ???
               # $argp - (pointer) ???
               # $new_func - function pointer ??? (CRYPTO_EX_new *)
               # $dup_func - function pointer ??? (CRYPTO_EX_dup *)
               # $free_func - function pointer ??? (CRYPTO_EX_free *)
               #
               # returns: (integer) ???

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_ex_new_index.html>

       •   CTX_get_mode

           Returns the mode set for ctx.

               my $rv = Net::SSLeay::CTX_get_mode($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: mode (bitmask)

               # to decode the return value (bitmask) use:
               # 0x00000001 corresponds to SSL_MODE_ENABLE_PARTIAL_WRITE
               # 0x00000002 corresponds to SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER
               # 0x00000004 corresponds to SSL_MODE_AUTO_RETRY
               # 0x00000008 corresponds to SSL_MODE_NO_AUTO_CHAIN
               # 0x00000010 corresponds to SSL_MODE_RELEASE_BUFFERS
               # (note: some of the bits might not be supported by older openssl versions)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_mode.html>

       •   CTX_set_mode

           Adds the mode set via bitmask in $mode to $ctx. Options already  set
           before are not cleared.

               my $rv = Net::SSLeay::CTX_set_mode($ctx, $mode);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $mode - mode bitmask
               #
               # returns: the new mode bitmask after adding $mode

           For bitmask details see "CTX_get_mode" (above).

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_mode.html>

       •   CTX_get_options

           Returns the options (bitmask) set for $ctx.

               my $rv = Net::SSLeay::CTX_get_options($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: options (bitmask)

           BEWARE: The available constants and their values in  bitmask  depend
           on  the TLS library. For example, SSL_OP_NO_TLSv1_3 became available
           much later than SSL_OP_NO_COMPRESS which is  already  deprecated  by
           some  libraries.  Also, some previously used option values have been
           recycled and are now  used  for  newer  options.  See  the  list  of
           constants   in  this  document  for  options  Net::SSLeay  currently
           supports.

           You are strongly encouraged to check your TLS library if you need to
           use numeric values directly. The following is a sample  of  historic
           values. It may not be correct anymore.

               # to decode the return value (bitmask) use:
               # 0x00000004 corresponds to SSL_OP_LEGACY_SERVER_CONNECT
               # 0x00000800 corresponds to SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
               # 0x00004000 corresponds to SSL_OP_NO_TICKET
               # 0x00010000 corresponds to SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
               # 0x00400000 corresponds to SSL_OP_CIPHER_SERVER_PREFERENCE
               # 0x04000000 corresponds to SSL_OP_NO_TLSv1

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_options.html>

       •   CTX_set_options

           Adds the options set via bitmask in $options to ctx. Options already
           set before are not cleared.

               Net::SSLeay::CTX_set_options($ctx, $options);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $options - options bitmask
               #
               # returns: the new options bitmask after adding $options

           For bitmask details see "CTX_get_options" (above).

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_options.html>

       •   CTX_get_quiet_shutdown

           Returns the 'quiet shutdown' setting of $ctx.

               my $rv = Net::SSLeay::CTX_get_quiet_shutdown($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: (integer) the current setting

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_quiet_shutdown.html>

       •   CTX_get_read_ahead

               my $rv = Net::SSLeay::CTX_get_read_ahead($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: (integer) read_ahead value

       •   CTX_get_session_cache_mode

           Returns the currently used cache mode (bitmask).

               my $rv = Net::SSLeay::CTX_get_session_cache_mode($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: mode (bitmask)

           BEWARE: SESS_CACHE_OFF and other  constants  are  not  available  in
           Net-SSLeay-1.82 and before.  If the constants are not available, the
           following  values  have  historically been correct. You are strongly
           encouraged to check your TLS library for the current values.

               # to decode the return value (bitmask) use:
               # 0x0000 corresponds to SSL_SESS_CACHE_OFF
               # 0x0001 corresponds to SSL_SESS_CACHE_CLIENT
               # 0x0002 corresponds to SSL_SESS_CACHE_SERVER
               # 0x0080 corresponds to SSL_SESS_CACHE_NO_AUTO_CLEAR
               # 0x0100 corresponds to SSL_SESS_CACHE_NO_INTERNAL_LOOKUP
               # 0x0200 corresponds to SSL_SESS_CACHE_NO_INTERNAL_STORE
               # (note: some of the bits might not be supported by older openssl versions)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_session_cache_mode.html>

       •   CTX_set_session_cache_mode

           Enables/disables session caching by setting the operational mode for
           $ctx to $mode.

               my $rv = Net::SSLeay::CTX_set_session_cache_mode($ctx, $mode);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $mode - mode (bitmask)
               #
               # returns: previously set cache mode

           For bitmask details see "CTX_get_session_cache_mode" (above).

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_session_cache_mode.html>

       •   CTX_get_timeout

           Returns the currently set timeout value for $ctx.

               my $rv = Net::SSLeay::CTX_get_timeout($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: timeout in seconds

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_timeout.html>

       •   CTX_get_verify_depth

           Returns  the  verification  depth limit currently set in $ctx. If no
           limit has been explicitly set, -1 is returned and the default  value
           will be used.

               my $rv = Net::SSLeay::CTX_get_verify_depth($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: depth limit currently set in $ctx, -1 if no limit has been explicitly set

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_verify_mode.html>

       •   CTX_get_verify_mode

           Returns the verification mode (bitmask) currently set in $ctx.

               my $rv = Net::SSLeay::CTX_get_verify_mode($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: mode (bitmask)

           For bitmask details see "CTX_set_verify".

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_verify_mode.html>

       •   CTX_set_verify

           Sets  the  verification flags for $ctx to be $mode and specifies the
           verify_callback function to be used.

               Net::SSLeay::CTX_set_verify($ctx, $mode, $callback);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $mode - mode (bitmask), see OpenSSL manual
               # $callback - [optional] reference to perl callback function
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_verify.html>

       •   CTX_set_post_handshake_auth

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at least OpenSSL 1.1.1, not in LibreSSL

           Enable  the  Post-Handshake  Authentication extension to be added to
           the ClientHello  such  that  post-handshake  authentication  can  be
           requested by the server.

               Net::SSLeay::CTX_set_posthandshake_auth($ctx, $val);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $val - 0 then the extension is not sent, otherwise it is
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_post_handshake_auth.html>

       •   CTX_load_verify_locations

           Specifies the locations for  $ctx,  at  which  CA  certificates  for
           verification  purposes  are  located. The certificates available via
           $CAfile and $CApath are trusted.

               my $rv = Net::SSLeay::CTX_load_verify_locations($ctx, $CAfile, $CApath);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $CAfile - (string) file of CA certificates in PEM format, the file can contain several CA certificates (or '')
               # $CApath - (string) directory containing CA certificates in PEM format (or '')
               #
               # returns: 1 on success, 0 on failure (check the error stack to find out the reason)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_load_verify_locations.html>

       •   CTX_need_tmp_RSA

           Return                 the                 result                 of
           "SSL_CTX_ctrl(ctx,SSL_CTRL_NEED_TMP_RSA,0,NULL)"

               my $rv = Net::SSLeay::CTX_need_tmp_RSA($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: result of SSL_CTRL_NEED_TMP_RSA command

           Not available with OpenSSL 1.1 and later.

       •   CTX_new

           The same as "CTX_v23_new"

               my $rv = Net::SSLeay::CTX_new();
               #
               # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_new.html>

           Not available with OpenSSL 1.1 and later.

       •   CTX_v2_new

           Creates  a  new  SSL_CTX  object  -  based  on  SSLv2_method()  - as
           framework to establish TLS/SSL enabled connections.

               my $rv = Net::SSLeay::CTX_v2_new();
               #
               # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

       •   CTX_v23_new

           Creates a new  SSL_CTX  object  -  based  on  SSLv23_method()  -  as
           framework to establish TLS/SSL enabled connections.

               my $rv = Net::SSLeay::CTX_v23_new();
               #
               # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

       •   CTX_v3_new

           Creates  a  new  SSL_CTX  object  -  based  on  SSLv3_method()  - as
           framework to establish TLS/SSL enabled connections.

               my $rv = Net::SSLeay::CTX_v3_new();
               #
               # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

       •   CTX_tlsv1_new

           COMPATIBILITY: Requires OpenSSL or LibreSSL built with  support  for
           TLSv1.

           Creates  a  new  SSL_CTX  object  -  based  on TLSv1_method() - as a
           framework for establishing connections using TLSv1.

               my $rv = Net::SSLeay::CTX_tlsv1_new();
               #
               # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

       •   CTX_tlsv1_1_new

           COMPATIBILITY: Requires OpenSSL >=  1.0.1  or  LibreSSL  built  with
           support for TLSv1.1.

           Creates  a  new  SSL_CTX  object  - based on TLSv1_1_method() - as a
           framework for establishing connections using TLSv1.1.

               my $rv = Net::SSLeay::CTX_tlsv1_1_new();
               #
               # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

       •   CTX_tlsv1_2_new

           COMPATIBILITY: Requires OpenSSL >=  1.0.1  or  LibreSSL  built  with
           support for TLSv1.2.

           Creates  a  new  SSL_CTX  object  - based on TLSv1_2_method() - as a
           framework for establishing connections using TLSv1.2.

               my $rv = Net::SSLeay::CTX_tlsv1_2_new();
               #
               # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

       •   CTX_new_with_method

           Creates a new SSL_CTX object based on $meth method

               my $rv = Net::SSLeay::CTX_new_with_method($meth);
               # $meth - value corresponding to openssl's SSL_METHOD structure
               #
               # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

               # example
               my $ctx = Net::SSLeay::CTX_new_with_method(&Net::SSLeay::TLSv1_method);

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_new.html>

       •   CTX_set_min_proto_version,                CTX_set_max_proto_version,
           set_min_proto_version and set_max_proto_version,

           COMPATIBILITY: not available in Net-SSLeay-1.82 and before; requires
           at least OpenSSL 1.1.0-pre2 or LibreSSL 2.6.0

           Set the minimum and maximum supported protocol for $ctx or $ssl.

               my $rv = Net::SSLeay::CTX_set_min_proto_version($ctx, $version);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $version - (integer) constant version value or 0 for automatic lowest or highest value
               #
               # returns: 1 on success, 0 on failure

               # example: allow only TLS 1.2 for a SSL_CTX
               my $rv_min = Net::SSLeay::CTX_set_min_proto_version($ctx, Net::SSLeay::TLS1_2_VERSION());
               my $rv_max = Net::SSLeay::CTX_set_max_proto_version($ctx, Net::SSLeay::TLS1_2_VERSION());

               # example: allow only TLS 1.1 for a SSL
               my $rv_min = Net::SSLeay::set_min_proto_version($ssl, Net::SSLeay::TLS1_1_VERSION());
               my $rv_max = Net::SSLeay::set_max_proto_version($ssl, Net::SSLeay::TLS1_1_VERSION());

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_min_proto_version.html>

       •   CTX_get_min_proto_version,                CTX_get_max_proto_version,
           get_min_proto_version and get_max_proto_version,

           COMPATIBILITY: not available in Net-SSLeay-1.82 and before; requires
           at least OpenSSL 1.1.0g

           Get the minimum and maximum supported protocol for $ctx or $ssl.

               my $version = Net::SSLeay::CTX_get_min_proto_version($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: 0 automatic lowest or highest value, configured value otherwise

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_min_proto_version.html>

       •   CTX_remove_session

           Removes the session $ses from the context $ctx.

               my $rv = Net::SSLeay::CTX_remove_session($ctx, $ses);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $ses - value corresponding to openssl's SSL_SESSION structure
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_add_session.html>

       •   CTX_sess_accept

               my $rv = Net::SSLeay::CTX_sess_accept($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: number of started SSL/TLS handshakes in server mode

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_number.html>

       •   CTX_sess_accept_good

               my $rv = Net::SSLeay::CTX_sess_accept_good($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: number of successfully established SSL/TLS sessions in server mode

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_number.html>

       •   CTX_sess_accept_renegotiate

               my $rv = Net::SSLeay::CTX_sess_accept_renegotiate($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: number of start renegotiations in server mode

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_number.html>

       •   CTX_sess_cache_full

               my $rv = Net::SSLeay::CTX_sess_cache_full($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: number of sessions that were removed because the maximum session cache size was exceeded

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_number.html>

       •   CTX_sess_cb_hits

               my $rv = Net::SSLeay::CTX_sess_cb_hits($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: number of successfully retrieved sessions from the external session cache in server mode

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_number.html>

       •   CTX_sess_connect

               my $rv = Net::SSLeay::CTX_sess_connect($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: number of started SSL/TLS handshakes in client mode

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_number.html>

       •   CTX_sess_connect_good

                my $rv = Net::SSLeay::CTX_sess_connect_good($ctx);
                # $ctx - value corresponding to openssl's SSL_CTX structure
                #
                # returns: number of successfully established SSL/TLS sessions in client mode

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_number.html>

       •   CTX_sess_connect_renegotiate

                my $rv = Net::SSLeay::CTX_sess_connect_renegotiate($ctx);
                # $ctx - value corresponding to openssl's SSL_CTX structure
                #
                # returns: number of start renegotiations in client mode

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_number.html>

       •   CTX_sess_get_cache_size

           Returns the currently valid session cache size.

                my $rv = Net::SSLeay::CTX_sess_get_cache_size($ctx);
                # $ctx - value corresponding to openssl's SSL_CTX structure
                #
                # returns: current size

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_set_cache_size.html>

       •   CTX_sess_hits

                my $rv = Net::SSLeay::CTX_sess_hits($ctx);
                # $ctx - value corresponding to openssl's SSL_CTX structure
                #
                # returns: number of successfully reused sessions

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_number.html>

       •   CTX_sess_misses

                my $rv = Net::SSLeay::CTX_sess_misses($ctx);
                # $ctx - value corresponding to openssl's SSL_CTX structure
                #
                # returns: number of sessions proposed by clients that were not found in the internal session cache in server mode

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_number.html>

       •   CTX_sess_number

                my $rv = Net::SSLeay::CTX_sess_number($ctx);
                # $ctx - value corresponding to openssl's SSL_CTX structure
                #
                # returns: current number of sessions in the internal session cache

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_number.html>

       •   CTX_sess_set_cache_size

           Sets the size of the internal  session  cache  of  context  $ctx  to
           $size.

                Net::SSLeay::CTX_sess_set_cache_size($ctx, $size);
                # $ctx - value corresponding to openssl's SSL_CTX structure
                # $size - cache size (0 = unlimited)
                #
                # returns: previously valid size

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_set_cache_size.html>

       •   CTX_sess_timeouts

           Returns the number of sessions proposed by clients and either  found
           in  the  internal or external session cache in server mode, but that
           were invalid due to timeout. These sessions are not included in  the
           SSL_CTX_sess_hits count.

               my $rv = Net::SSLeay::CTX_sess_timeouts($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: number of sessions

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_number.html>

       •   CTX_sess_set_new_cb

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before

           Sets the callback function, which is automatically called whenever a
           new session was negotiated.

               Net::SSLeay::CTX_sess_set_new_cb($ctx, $func);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $func - perl reference to callback function
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_set_new_cb.html>

       •   CTX_sess_set_remove_cb

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before

           Sets the callback function, which is automatically called whenever a
           session is removed by the SSL engine.

               Net::SSLeay::CTX_sess_set_remove_cb($ctx, $func);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $func - perl reference to callback function
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_set_remove_cb.html>

       •   CTX_sessions

           Returns a pointer to the lhash  databases  containing  the  internal
           session cache for ctx.

               my $rv = Net::SSLeay::CTX_sessions($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: value corresponding to openssl's LHASH structure (0 on failure)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sessions.html>

       •   CTX_set1_param

           COMPATIBILITY: requires at least OpenSSL 1.0.0-beta3

           Applies X509 verification parameters $vpm on $ctx

               my $rv = Net::SSLeay::CTX_set1_param($ctx, $vpm);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $vpm - value corresponding to openssl's X509_VERIFY_PARAM structure
               #
               # returns: 1 on success, 0 on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get0_param.html>

       •   CTX_set_cert_store

           Sets/replaces  the  certificate verification storage of $ctx to/with
           $store.

               Net::SSLeay::CTX_set_cert_store($ctx, $store);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $store - value corresponding to openssl's X509_STORE structure
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_cert_store.html>

       •   CTX_set_cert_verify_callback

           Sets  the  verification callback function for $ctx. SSL objects that
           are created from $ctx inherit the setting valid  at  the  time  when
           Net::SSLeay::new($ctx) is called.

               Net::SSLeay::CTX_set_cert_verify_callback($ctx, $func, $data);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $func - perl reference to callback function
               # $data - [optional] data that will be passed to callback function when invoked
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_cert_verify_callback.html>

       •   CTX_set_cipher_list

           Sets the list of available ciphers for $ctx using the control string
           $str.  The list of ciphers is inherited by all ssl  objects  created
           from $ctx.

               my $rv = Net::SSLeay::CTX_set_cipher_list($s, $str);
               # $s - value corresponding to openssl's SSL_CTX structure
               # $str - (string) cipher list e.g. '3DES:+RSA'
               #
               # returns: 1 if any cipher could be selected and 0 on complete failure

           The       format       of       $str       is      described      in
           <https://www.openssl.org/docs/manmaster/man1/openssl-ciphers.html>

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_cipher_list.html>

       •   CTX_set_ciphersuites

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at   least   OpenSSL   1.1.1   or   at   least  LibreSSL  3.4.0  and
           Net-SSLeay-1.94

           Configure the available TLSv1.3 ciphersuites.

               my $rv = Net::SSLeay::CTX_set_ciphersuites($ctx, $str);
               # $ctx  - value corresponding to openssl's SSL_CTX structure
               # $str  - colon (":") separated list of TLSv1.3 ciphersuite names in order of preference
               #
               # returns: (integer) 1 if the requested ciphersuite list was configured, and 0 otherwise

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_ciphersuites.html>

       •   CTX_set_client_CA_list

           Sets  the  list  of  CAs sent to the client when requesting a client
           certificate for $ctx.

               Net::SSLeay::CTX_set_client_CA_list($ctx, $list);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $list - value corresponding to openssl's X509_NAME_STACK structure
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_client_CA_list.html>

       •   CTX_set_default_passwd_cb

           Sets the default password callback called when loading/storing a PEM
           certificate with encryption.

               Net::SSLeay::CTX_set_default_passwd_cb($ctx, $func);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $func - perl reference to callback function
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_default_passwd_cb.html>

       •   CTX_set_default_passwd_cb_userdata

           Sets a pointer to userdata which will be provided  to  the  password
           callback on invocation.

               Net::SSLeay::CTX_set_default_passwd_cb_userdata($ctx, $userdata);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $userdata - data that will be passed to callback function when invoked
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_default_passwd_cb.html>

       •   CTX_set_default_verify_paths

           ??? (more info needed)

               my $rv = Net::SSLeay::CTX_set_default_verify_paths($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: 1 on success, 0 on failure

       •   CTX_set_ex_data

           Is used to store application data at $data for $idx  into  the  $ctx
           object.

               my $rv = Net::SSLeay::CTX_set_ex_data($ssl, $idx, $data);
               # $ssl - value corresponding to openssl's SSL_CTX structure
               # $idx - (integer) ???
               # $data - (pointer) ???
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_ex_new_index.html>

       •   CTX_set_purpose

               my $rv = Net::SSLeay::CTX_set_purpose($s, $purpose);
               # $s - value corresponding to openssl's SSL_CTX structure
               # $purpose - (integer) purpose identifier
               #
               # returns: 1 on success, 0 on failure

               # available purpose identifier
               # 1 - X509_PURPOSE_SSL_CLIENT
               # 2 - X509_PURPOSE_SSL_SERVER
               # 3 - X509_PURPOSE_NS_SSL_SERVER
               # 4 - X509_PURPOSE_SMIME_SIGN
               # 5 - X509_PURPOSE_SMIME_ENCRYPT
               # 6 - X509_PURPOSE_CRL_SIGN
               # 7 - X509_PURPOSE_ANY
               # 8 - X509_PURPOSE_OCSP_HELPER
               # 9 - X509_PURPOSE_TIMESTAMP_SIGN

               # or use corresponding constants
               $purpose = &Net::SSLeay::X509_PURPOSE_SSL_CLIENT;
               # ...
               $purpose = &Net::SSLeay::X509_PURPOSE_TIMESTAMP_SIGN;

       •   CTX_set_quiet_shutdown

           Sets the 'quiet shutdown' flag for $ctx  to  be  mode.  SSL  objects
           created   from   $ctx   inherit   the   mode   valid   at  the  time
           Net::SSLeay::new($ctx) is called.

               Net::SSLeay::CTX_set_quiet_shutdown($ctx, $mode);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $mode - 0 or 1
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_quiet_shutdown.html>

       •   CTX_set_read_ahead

               my $rv = Net::SSLeay::CTX_set_read_ahead($ctx, $val);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $val - read_ahead value to be set
               #
               # returns: the original read_ahead value

       •   CTX_set_session_id_context

           Sets  the  context  $sid_ctx  of  length $sid_ctx_len within which a
           session can be reused for the $ctx object.

               my $rv = Net::SSLeay::CTX_set_session_id_context($ctx, $sid_ctx, $sid_ctx_len);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $sid_ctx - data buffer
               # $sid_ctx_len - length of data in $sid_ctx
               #
               # returns: 1 on success, 0 on failure (the error is logged to the error stack)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_session_id_context.html>

       •   CTX_set_ssl_version

           Sets a new default TLS/SSL method for SSL objects newly created from
           this  $ctx.  SSL objects already created with Net::SSLeay::new($ctx)
           are not  affected,  except  when  Net::SSLeay:clear($ssl)  is  being
           called.

               my $rv = Net::SSLeay::CTX_set_ssl_version($ctx, $meth);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $meth - value corresponding to openssl's SSL_METHOD structure
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_ssl_version.html>

       •   CTX_set_timeout

           Sets the timeout for newly created sessions  for  $ctx  to  $t.  The
           timeout value $t must be given in seconds.

               my $rv = Net::SSLeay::CTX_set_timeout($ctx, $t);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $t - timeout in seconds
               #
               # returns: previously set timeout value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_timeout.html>

       •   CTX_set_tmp_dh

           Sets DH parameters to be used to be $dh. The key is inherited by all
           ssl objects created from $ctx.

               my $rv = Net::SSLeay::CTX_set_tmp_dh($ctx, $dh);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $dh - value corresponding to openssl's DH structure
               #
               # returns: 1 on success, 0 on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_tmp_dh_callback.html>

       •   CTX_set_tmp_dh_callback

           Sets  the callback function for $ctx to be used when a DH parameters
           are required to $tmp_dh_callback.

               Net::SSLeay::CTX_set_tmp_dh_callback($ctx, $tmp_dh_callback);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # tmp_dh_callback - (function pointer) ???
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_tmp_dh_callback.html>

       •   CTX_set_tmp_rsa

           Sets the temporary/ephemeral RSA key to be used to be $rsa.

               my $rv = Net::SSLeay::CTX_set_tmp_rsa($ctx, $rsa);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $rsa - value corresponding to openssl's RSA structure
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/man1.0.2/man3/SSL_CTX_set_tmp_rsa_callback.html>

           Not available with OpenSSL 1.1 and later.

       •   CTX_set_tmp_rsa_callback

           Sets  the  callback  function  for   ctx   to   be   used   when   a
           temporary/ephemeral RSA key is required to $tmp_rsa_callback.

           ??? (does this function really work?)

               Net::SSLeay::CTX_set_tmp_rsa_callback($ctx, $tmp_rsa_callback);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $tmp_rsa_callback - (function pointer) ???
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/man1.0.2/man3/SSL_CTX_set_tmp_rsa_callback.html>

           Not available with OpenSSL 1.1 and later.

       •   CTX_set_trust

               my $rv = Net::SSLeay::CTX_set_trust($s, $trust);
               # $s - value corresponding to openssl's SSL_CTX structure
               # $trust - (integer) trust identifier
               #
               # returns: the original value

               # available trust identifiers
               # 1 - X509_TRUST_COMPAT
               # 2 - X509_TRUST_SSL_CLIENT
               # 3 - X509_TRUST_SSL_SERVER
               # 4 - X509_TRUST_EMAIL
               # 5 - X509_TRUST_OBJECT_SIGN
               # 6 - X509_TRUST_OCSP_SIGN
               # 7 - X509_TRUST_OCSP_REQUEST
               # 8 - X509_TRUST_TSA

               # or use corresponding constants
               $trust = &Net::SSLeay::X509_TRUST_COMPAT;
               # ...
               $trust = &Net::SSLeay::X509_TRUST_TSA;

       •   CTX_set_verify_depth

           Sets the maximum depth for the certificate chain  verification  that
           shall be allowed for ctx.

               Net::SSLeay::CTX_set_verify_depth($ctx, $depth);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $depth - max. depth
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_verify.html>

       •   CTX_use_PKCS12_file

           Adds the certificate and private key from PKCS12  file  $p12filename
           to $ctx.

               my $rv = Net::SSLeay::CTX_use_PKCS12_file($ctx, $p12filename, $password);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $p12filename - (string) filename
               # $password - (string) password to decrypt private key
               #
               # returns: 1 on success, 0 on failure

           NOTE  Net::SSLeay  1.92_01  and  earlier:  With some combinations of
           Windows, perl, compiler and compiler options, you may see a  runtime
           error        "no        OPENSSL_Applink",        when        calling
           Net::SSLeay::CTX_use_PKCS12_file. See README.Win32 for more details.

       •   CTX_use_PrivateKey

           Adds the private key $pkey to $ctx.

               my $rv = Net::SSLeay::CTX_use_PrivateKey($ctx, $pkey);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $pkey - value corresponding to openssl's EVP_PKEY structure
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   CTX_use_PrivateKey_file

           Adds the first private key found in $file to $ctx.

               my $rv = Net::SSLeay::CTX_use_PrivateKey_file($ctx, $file, $type);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $file - (string) file name
               # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   CTX_use_RSAPrivateKey

           Adds the RSA private key $rsa to $ctx.

               my $rv = Net::SSLeay::CTX_use_RSAPrivateKey($ctx, $rsa);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $rsa - value corresponding to openssl's RSA structure
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   CTX_use_RSAPrivateKey_file

           Adds the first RSA private key found in $file to $ctx.

               my $rv = Net::SSLeay::CTX_use_RSAPrivateKey_file($ctx, $file, $type);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $file - (string) file name
               # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

       •   CTX_use_certificate

           Loads the certificate $x into $ctx

               my $rv = Net::SSLeay::CTX_use_certificate($ctx, $x);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $x - value corresponding to openssl's X509 structure
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   CTX_use_certificate_chain_file

           Loads a certificate chain from $file  into  $ctx.  The  certificates
           must be in PEM format and must be sorted starting with the subject's
           certificate  (actual  client  or  server  certificate),  followed by
           intermediate CA  certificates  if  applicable,  and  ending  at  the
           highest level (root) CA.

               my $rv = Net::SSLeay::CTX_use_certificate_chain_file($ctx, $file);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $file - (string) file name
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   CTX_use_certificate_file

           Loads the first certificate stored in $file into $ctx.

               my $rv = Net::SSLeay::CTX_use_certificate_file($ctx, $file, $type);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $file - (string) file name
               # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   CTX_get_security_level

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at   least   OpenSSL   1.1.0   or   at   least  LibreSSL  3.6.0  and
           Net-SSLeay-1.94

           Returns the security level associated with $ctx.

               my $level = Net::SSLeay::CTX_get_security_level($ctx);
               # $ctx   - value corresponding to openssl's SSL_CTX structure
               #
               # returns: (integer) current security level

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_security_level.html>

       •   CTX_set_security_level

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at   least   OpenSSL   1.1.0   or   at   least  LibreSSL  3.6.0  and
           Net-SSLeay-1.94

           Sets the security level associated with $ctx to $level.

               Net::SSLeay::CTX_set_security_level($ctx, $level);
               # $ssl   - value corresponding to openssl's SSL_CTX structure
               # $level - new security level
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_security_level.html>

       •   CTX_set_num_tickets

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at   least   OpenSSL   1.1.1   or   at   least  LibreSSL  3.5.0  and
           Net-SSLeay-1.94

           Set number of TLSv1.3 session tickets that will be sent to a client.

               my $rv = Net::SSLeay::CTX_set_num_tickets($ctx, $number_of_tickets);
               # $ctx  - value corresponding to openssl's SSL_CTX structure
               # $number_of_tickets - number of tickets to send
               #
               # returns: 1 on success, 0 on failure

           Set to zero if you do not no want to support a session resumption.

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_num_tickets.html>

       •   CTX_get_num_tickets

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at   least   OpenSSL   1.1.1   or   at   least  LibreSSL  3.5.0  and
           Net-SSLeay-1.94

           Get number of TLSv1.3 session tickets that will be sent to a client.

               my $number_of_tickets = Net::SSLeay::CTX_get_num_tickets($ctx);
               # $ctx  - value corresponding to openssl's SSL_CTX structure
               #
               # returns: (integer) number of tickets to send

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_num_tickets.html>

       •   CTX_set_keylog_callback

           COMPATIBILITY: not available in Net-SSLeay-1.90 and before; requires
           at   least   OpenSSL  1.1.1pre1  or  at  least  LibreSSL  3.5.0  and
           Net-SSLeay-1.94

           Set the TLS key logging callback.

               Net::SSLeay::CTX_set_keylog_callback($ctx, $cb);
               # $ctx  - value corresponding to openssl's SSL_CTX structure
               # $cb - reference to a perl callback function
               #
               # returns: no return value

           The callback function will be called like this:

               keylog_cb_func($ssl, $line);
               # $ssl - value corresponding to OpenSSL's SSL object associated with the connection
               # $line - a string containing the key material in the format used by NSS for its SSLKEYLOGFILE debugging output

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_keylog_callback.html>

       •   CTX_get_keylog_callback

           COMPATIBILITY: not available in Net-SSLeay-1.90 and before; requires
           at   least   OpenSSL  1.1.1pre1  or  at  least  LibreSSL  3.5.0  and
           Net-SSLeay-1.94

           Retrieve the previously set TLS key logging callback.

               my $cb = Net::SSLeay::CTX_get_keylog_callback($ctx);
               # $ctx  - value corresponding to openssl's SSL_CTX structure
               #
               # returns: a reference to a perl callback function or undef if no callback is set

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_keylog_callback.html>

       •   CTX_set_client_hello_cb

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.1pre1, not in LibreSSL

           Set   a   callback  function  called  during  the  early  stages  of
           ClientHello processing on the server.  When callback is  undef,  the
           existing callback is disabled.

               Net::SSLeay::CTX_set_client_hello_cb($ctx, $f, [$arg]);
               # $ctx  - value corresponding to openssl's SSL_CTX structure
               # $f - sub { my ($ssl, $arg) = @_; ...; return ($ret, $al); }
               # $arg - optional data passed to the callback function when invoked
               #
               # returns: no return value

           The callback function will be called like this:

               client_hello_cb_func($ssl, $arg);
               # $ssl - value corresponding to OpenSSL's SSL object associated with the connection
               # $arg - data to callback
               #
               # An alert code must be returned with SSL_CLIENT_HELLO_FAILURE.
               # Return value examples:
               # ok: return Net::SSLeay::CLIENT_HELLO_SUCCESS();
               # suspend: return Net::SSLeay::CLIENT_HELLO_RETRY();
               # error: return (Net::SSLeay::CLIENT_HELLO_FAILURE(), Net::SSLeay::AD_NO_APPLICATION_PROTOCOL());

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_client_hello_cb.html>

       Low level API: SSL_* related functions

       NOTE: Please note that the  function  described  in  this  chapter  have
       "SSL_" part stripped from their original openssl names.

       •   new

           Creates  a  new SSL structure which is needed to hold the data for a
           TLS/SSL connection.  The new structure inherits the settings of  the
           underlying   context   $ctx:   connection  method  (SSLv2/v3/TLSv1),
           options, verification settings, timeout settings.

               my $rv = Net::SSLeay::new($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: value corresponding to openssl's SSL structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_new.html>

       •   accept

           Waits  for  a  TLS/SSL client to initiate the TLS/SSL handshake. The
           communication channel must already have been set and assigned to the
           ssl by setting an underlying BIO.

               my $rv = Net::SSLeay::accept($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: 1 = success, 0 = handshake not successful, <0 = fatal error during handshake

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_accept.html>

       •   add_client_CA

           Adds  the  CA  name extracted from cacert to the list of CAs sent to
           the client when requesting a client certificate for the chosen  ssl,
           overriding the setting valid for ssl's SSL_CTX object.

               my $rv = Net::SSLeay::add_client_CA($ssl, $x);
               # $ssl - value corresponding to openssl's SSL structure
               # $x - value corresponding to openssl's X509 structure
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_client_CA_list.html>

       •   callback_ctrl

           ??? (more info needed)

               my $rv = Net::SSLeay::callback_ctrl($ssl, $cmd, $fp);
               # $ssl - value corresponding to openssl's SSL structure
               # $cmd - (integer) command id
               # $fp - (function pointer) ???
               #
               # returns: ???

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_ctrl.html>

       •   check_private_key

           Checks  the  consistency  of  a  private  key with the corresponding
           certificate loaded into $ssl

               my $rv = Net::SSLeay::check_private_key($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   clear

           Reset SSL object to allow another connection.

               Net::SSLeay::clear($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_clear.html>

       •   connect

           Initiate the TLS/SSL handshake with an TLS/SSL server.

               my $rv = Net::SSLeay::connect($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: 1 = success, 0 = handshake not successful, <0 = fatal error during handshake

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_connect.html>

       •   copy_session_id

           Copies  the  session  structure fro $from to $to (+ also the private
           key and certificate associated with $from).

               Net::SSLeay::copy_session_id($to, $from);
               # $to - value corresponding to openssl's SSL structure
               # $from - value corresponding to openssl's SSL structure
               #
               # returns: no return value

       •   ctrl

           Internal handling function for SSL objects.

           BEWARE: openssl doc says:  This  function  should  never  be  called
           directly!

               my $rv = Net::SSLeay::ctrl($ssl, $cmd, $larg, $parg);
               # $ssl - value corresponding to openssl's SSL structure
               # $cmd - (integer) command id
               # $larg - (integer) long ???
               # $parg - (string/pointer) ???
               #
               # returns: (long) result of given command ???

           For more details about valid $cmd values check "CTX_ctrl".

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_ctrl.html>

       •   do_handshake

           Will wait for a SSL/TLS handshake to take place. If  the  connection
           is  in  client  mode,  the  handshake will be started. The handshake
           routines may have to be  explicitly  set  in  advance  using  either
           SSL_set_connect_state or SSL_set_accept_state(3).

               my $rv = Net::SSLeay::do_handshake($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: 1 = success, 0 = handshake not successful, <0 = fatal error during handshake

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_do_handshake.html>

       •   dup

           Returns a duplicate of $ssl.

               my $rv = Net::SSLeay::dup($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: value corresponding to openssl's SSL structure (0 on failure)

       •   free

           Free an allocated SSL structure.

               Net::SSLeay::free($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_free.html>

       •   get0_param

           COMPATIBILITY: not available in Net-SSLeay-1.82 and before; requires
           at least OpenSSL 1.0.2-beta1 or LibreSSL 2.7.0

           Returns the current verification parameters.

               my $vpm = Net::SSLeay::get0_param($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: value corresponding to openssl's X509_VERIFY_PARAM structure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get0_param.html>

       •   get_SSL_CTX

           Returns a pointer to the SSL_CTX object, from which $ssl was created
           with Net::SSLeay::new.

               my $rv = Net::SSLeay::get_SSL_CTX($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_SSL_CTX.html>

       •   set_SSL_CTX

           COMPATIBILITY: requires at least OpenSSL 0.9.8f

           Sets the SSL_CTX the corresponds to an SSL session.

               my $the_ssl_ctx = Net::SSLeay::set_SSL_CTX($ssl, $ssl_ctx);
               # $ssl - value corresponding to openssl's SSL structure
               # $ssl_ctx - Change the ssl object to the given ssl_ctx
               #
               # returns - the ssl_ctx

       •   get_app_data

           Can be used to get application defined value/data.

               my $rv = Net::SSLeay::get_app_data($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: string/buffer/pointer ???

       •   set_app_data

           Can be used to set some application defined value/data.

               my $rv = Net::SSLeay::set_app_data($ssl, $arg);
               # $ssl - value corresponding to openssl's SSL structure
               # $arg - (string/buffer/pointer ???) data
               #
               # returns: ???

       •   get_certificate

           Gets X509 certificate from an established SSL connection.

               my $rv = Net::SSLeay::get_certificate($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: value corresponding to openssl's X509 structure (0 on failure)

       •   get_cipher

           Obtains the name of the currently used cipher.

               my $rv = Net::SSLeay::get_cipher($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: (string) cipher name e.g. 'DHE-RSA-AES256-SHA' or '', when no session has been established.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_current_cipher.html>

       •   get_cipher_bits

           Obtain the number of secret/algorithm bits used.

               my $rv = Net::SSLeay::get_cipher_bits($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: number of secret bits used by current cipher

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_current_cipher.html>
           and
           <https://www.openssl.org/docs/manmaster/man3/SSL_CIPHER_get_name.html>

       •   get_ciphers

           COMPATIBILITY: not available in Net-SSLeay-1.88 and before

           Returns a list of SSL_CIPHER structures available for $ssl sorted by
           preference

               my @ciphers = Net::SSLeay::get_ciphers($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: (list) SSL_CIPHER structures or nothing when $ssl is undefined or no ciphers are available

           Example:

               my @ciphers = Net::SSLeay::get_ciphers($ssl);
               foreach my $c (@ciphers) {
                   print Net::SSLeay::CIPHER_get_name($c) . "\n";
               }

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_ciphers.html>

       •   get_cipher_list

           Returns the name (string) of the SSL_CIPHER  listed  for  $ssl  with
           priority $n.

               my $rv = Net::SSLeay::get_cipher_list($ssl, $n);
               # $ssl - value corresponding to openssl's SSL structure
               # $n - (integer) priority
               #
               # returns: (string) cipher name e.g. 'EDH-DSS-DES-CBC3-SHA' or undef in case of error

           Call  Net::SSLeay::get_cipher_list  with priority starting from 0 to
           obtain  the  sorted  list  of  available  ciphers,  until  undef  is
           returned:

               my $priority = 0;
               while (my $c = Net::SSLeay::get_cipher_list($ssl, $priority)) {
                   print "cipher[$priority] = $c\n";
                   $priority++;
               }

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_cipher_list.html>

       •   get_client_CA_list

           Returns the list  of  client  CAs  explicitly  set  for  $ssl  using
           "Net::SSLeay::set_client_CA_list"  or  $ssl's  SSL_CTX  object  with
           "Net::SSLeay::CTX_set_client_CA_list", when in server mode.

           In client mode, returns the list of client CAs sent from the server,
           if any.

               my $rv = Net::SSLeay::get_client_CA_list($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: value corresponding to openssl's STACK_OF(X509_NAME) structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_client_CA_list.html>

       •   get_current_cipher

           Returns the cipher actually used.

               my $rv = Net::SSLeay::get_current_cipher($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: value corresponding to openssl's SSL_CIPHER structure (0 on failure)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_current_cipher.html>

       •   get_default_timeout

           Returns the default timeout value assigned  to  SSL_SESSION  objects
           negotiated for the protocol valid for $ssl.

               my $rv = Net::SSLeay::get_default_timeout($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: (long) timeout in seconds

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_default_timeout.html>

       •   get_error

           Returns a result code for a preceding call to  "connect",  "accept",
           "do_handshake", "read", "peek" or "write" on $ssl.

               my $rv = Net::SSLeay::get_error($ssl, $ret);
               # $ssl - value corresponding to openssl's SSL structure
               # $ret - return value of preceding TLS/SSL I/O operation
               #
               # returns: result code, which is one of the following values:
               #  0 - SSL_ERROR_NONE
               #  1 - SSL_ERROR_SSL
               #  2 - SSL_ERROR_WANT_READ
               #  3 - SSL_ERROR_WANT_WRITE
               #  4 - SSL_ERROR_WANT_X509_LOOKUP
               #  5 - SSL_ERROR_SYSCALL
               #  6 - SSL_ERROR_ZERO_RETURN
               #  7 - SSL_ERROR_WANT_CONNECT
               #  8 - SSL_ERROR_WANT_ACCEPT

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_error.html>

       •   get_ex_data

           Is used to retrieve the information for $idx from $ssl.

               my $rv = Net::SSLeay::get_ex_data($ssl, $idx);
               # $ssl - value corresponding to openssl's SSL structure
               # $idx - (integer) index for application specific data
               #
               # returns: pointer to ???

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_ex_new_index.html>

       •   set_ex_data

           Is  used  to  store application data at $data for $idx into the $ssl
           object.

               my $rv = Net::SSLeay::set_ex_data($ssl, $idx, $data);
               # $ssl - value corresponding to openssl's SSL structure
               # $idx - (integer) ???
               # $data - (pointer) ???
               #
               # returns: 1 on success, 0 on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_ex_new_index.html>

       •   get_ex_new_index

           Is used to register a new index for application specific data.

               my $rv = Net::SSLeay::get_ex_new_index($argl, $argp, $new_func, $dup_func, $free_func);
               # $argl - (long) ???
               # $argp - (pointer) ???
               # $new_func - function pointer ??? (CRYPTO_EX_new *)
               # $dup_func - function pointer ??? (CRYPTO_EX_dup *)
               # $free_func - function pointer ??? (CRYPTO_EX_free *)
               #
               # returns: (integer) ???

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_ex_new_index.html>

       •   get_fd

           Returns the file descriptor which is linked to $ssl.

               my $rv = Net::SSLeay::get_fd($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: file descriptor (>=0) or -1 on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_fd.html>

       •   get_finished

           Obtains the latest 'Finished' message sent to the peer. Return value
           is  zero  if  there's been no Finished message yet. Default count is
           2*EVP_MAX_MD_SIZE that  is  long  enough  for  all  possible  Finish
           messages.  If  you  supply a non-default count, the resulting return
           value may be longer than returned buf's length.

               my $rv = Net::SSLeay::get_finished($ssl, $buf, $count);
               # $ssl - value corresponding to openssl's SSL structure
               # $buf - buffer where the returned data will be stored
               # $count - [optional] max size of return data - default is 2*EVP_MAX_MD_SIZE
               #
               # returns: length of latest Finished message

       •   get_peer_finished

           Obtains the  latest  'Finished'  message  expected  from  the  peer.
           Parameters and return value are similar to get_finished().

               my $rv = Net::SSLeay::get_peer_finished($ssl, $buf, $count);
               # $ssl - value corresponding to openssl's SSL structure
               # $buf - buffer where the returned data will be stored
               # $count - [optional] max size of return data - default is 2*EVP_MAX_MD_SIZE
               #
               # returns: length of latest Finished message

       •   get_keyblock_size

           Gets the length of the TLS keyblock. Look for 'key_block' in TLS 1.2
           and  earlier TLS RFCs. Consider using TLS exporter interface defined
           by RFC 5705 instead of creating your own keying material exporter.

           NOTE: Does not exactly correspond to any  low  level  API  function.
           Intended for EAP-FAST.

               my $rv = Net::SSLeay::get_keyblock_size($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: keyblock size, -1 on error

       •   get_mode

           Returns the mode (bitmask) set for $ssl.

               my $rv = Net::SSLeay::get_mode($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: mode (bitmask)

           To   decode   the  return  value  (bitmask)  see  documentation  for
           "CTX_get_mode".

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_mode.html>

       •   set_mode

           Adds  the mode set via bitmask in $mode to $ssl. Options already set
           before are not cleared.

               my $rv = Net::SSLeay::set_mode($ssl, $mode);
               # $ssl - value corresponding to openssl's SSL structure
               # $mode - mode (bitmask)
               #
               # returns: the new mode bitmask after adding $mode

           For $mode bitmask details see "CTX_get_mode".

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_mode.html>

       •   get_options

           Returns the options (bitmask) set for $ssl.

               my $rv = Net::SSLeay::get_options($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: options (bitmask)

           To   decode   the  return  value  (bitmask)  see  documentation  for
           "CTX_get_options".

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_options.html>

       •   set_options

           Adds  the  options  set  via  bitmask  in  $options to $ssl. Options
           already set before are not cleared!

               Net::SSLeay::set_options($ssl, $options);
               # $ssl - value corresponding to openssl's SSL structure
               # $options - options (bitmask)
               #
               # returns: the new options bitmask after adding $options

           For $options bitmask details see "CTX_get_options".

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_options.html>

       •   get_peer_certificate

           Get the X509 certificate of the peer.

               my $rv = Net::SSLeay::get_peer_certificate($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: value corresponding to openssl's X509 structure (0 on failure)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_peer_certificate.html>

       •   get_peer_cert_chain

           Get  the  certificate  chain  of  the  peer  as  an  array  of  X509
           structures.

               my @chain = Net::SSLeay::get_peer_cert_chain($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: list of X509 structures

           Example:

               my @chain = Net::SSLeay::get_peer_cert_chain($ssl);
               foreach my $x509 (@chain) {
                   print Net::SSLeay::X509_NAME_oneline(Net::SSLeay::X509_get_subject_name($cert)) . "\n";
               }

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_peer_cert_chain.html>

       •   get_quiet_shutdown

           Returns the 'quiet shutdown' setting of ssl.

               my $rv = Net::SSLeay::get_quiet_shutdown($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: (integer) current 'quiet shutdown' value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_quiet_shutdown.html>

       •   get_rbio

           Get 'read' BIO linked to an SSL object $ssl.

               my $rv = Net::SSLeay::get_rbio($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: value corresponding to openssl's BIO structure (0 on failure)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_rbio.html>

       •   get_read_ahead

               my $rv = Net::SSLeay::get_read_ahead($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: (integer) read_ahead value

       •   set_read_ahead

               Net::SSLeay::set_read_ahead($ssl, $val);
               # $ssl - value corresponding to openssl's SSL structure
               # $val - read_ahead value to be set
               #
               # returns: the original read_ahead value

       •   get_security_level

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at  least  OpenSSL  1.1.0   or   at   least   LibreSSL   3.6.0   and
           Net-SSLeay-1.94

           Returns the security level associated with $ssl.

               my $level = Net::SSLeay::get_security_level($ssl);
               # $ssl   - value corresponding to openssl's SSL structure
               #
               # returns: (integer) current security level

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_security_level.html>

       •   set_security_level

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at  least  OpenSSL  1.1.0   or   at   least   LibreSSL   3.6.0   and
           Net-SSLeay-1.94

           Sets the security level associated with $ssl to $level.

               Net::SSLeay::set_security_level($ssl, $level);
               # $ssl   - value corresponding to openssl's SSL structure
               # $level - new security level
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_security_level.html>

       •   set_num_tickets

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at  least  OpenSSL  1.1.1   or   at   least   LibreSSL   3.5.0   and
           Net-SSLeay-1.94

           Set number of TLSv1.3 session tickets that will be sent to a client.

               my $rv = Net::SSLeay::set_num_tickets($ssl, $number_of_tickets);
               # $ssl  - value corresponding to openssl's SSL structure
               # $number_of_tickets - number of tickets to send
               #
               # returns: 1 on success, 0 on failure

           Set to zero if you do not no want to support a session resumption.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_num_tickets.html>

       •   get_num_tickets

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at  least  OpenSSL  1.1.1   or   at   least   LibreSSL   3.5.0   and
           Net-SSLeay-1.94

           Get number of TLSv1.3 session tickets that will be sent to a client.

               my $number_of_tickets = Net::SSLeay::get_num_tickets($ctx);
               # $ctx  - value corresponding to openssl's SSL structure
               #
               # returns: number of tickets to send

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_num_tickets.html>

       •   get_server_random

           Returns internal SSLv3 server_random value.

               Net::SSLeay::get_server_random($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: server_random value (binary data)

       •   get_client_random

           NOTE: Does not exactly correspond to any low level API function

           Returns internal SSLv3 client_random value.

               Net::SSLeay::get_client_random($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: client_random value (binary data)

       •   export_keying_material

           Returns keying material based on  the  string  $label  and  optional
           $context.  Note  that  with  TLSv1.2 and lower, empty context (empty
           string) and undefined context (no  value  or  'undef')  will  return
           different values.

               my $out = Net::SSLeay::export_keying_material($ssl, $olen, $label, $context);
               # $ssl - value corresponding to openssl's SSL structure
               # $olen - number of bytes to return
               # $label - application specific label
               # $context - [optional] context - default is undef for no context
               #
               # returns: keying material (binary data) or undef on error

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_export_keying_material.html>

       •   get_session

           Retrieve TLS/SSL session data used in $ssl. The reference  count  of
           the SSL_SESSION is NOT incremented.

               my $rv = Net::SSLeay::get_session($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: value corresponding to openssl's SSL_SESSION structure (0 on failure)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_session.html>

       •   SSL_get0_session

           The   alias   for   "get_session"   (note   that   the    name    is
           "SSL_get0_session" NOT "get0_session").

               my $rv = Net::SSLeay::SSL_get0_session();

       •   get1_session

           Returns  a  pointer  to  the  SSL_SESSION actually used in $ssl. The
           reference count of the SSL_SESSION is incremented by 1.

               my $rv = Net::SSLeay::get1_session($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: value corresponding to openssl's SSL_SESSION structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_session.html>

       •   get_shared_ciphers

           Returns  string  with a list (colon ':' separated) of ciphers shared
           between client and server within SSL session $ssl.

               my $rv = Net::SSLeay::get_shared_ciphers();
               #
               # returns: string like 'ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES256-SHA:DHE-DSS-AES256-SHA:...'

       •   get_shutdown

           Returns the shutdown mode of $ssl.

               my $rv = Net::SSLeay::get_shutdown($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: shutdown mode (bitmask) of ssl

               # to decode the return value (bitmask) use:
               # 0 - No shutdown setting, yet
               # 1 - SSL_SENT_SHUTDOWN
               # 2 - SSL_RECEIVED_SHUTDOWN

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_shutdown.html>

       •   get_ssl_method

           Returns a function pointer to the TLS/SSL method set in $ssl.

               my $rv = Net::SSLeay::get_ssl_method($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_ssl_version.html>

       •   in_init,     in_before,      is_init_finished,      in_connect_init,
           in_accept_init

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before.

           Retrieve   information   about  the  handshake  state  machine.  All
           functions take $ssl as the only argument and return 0  or  1.  These
           functions are recommended over get_state() and state().

               my $rv = Net::SSLeay::is_init_finished($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: All functions return 1 or 0

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_in_init.html>

       •   get_state

           COMPATIBILITY: OpenSSL 1.1.0 and later use different constants which
           are not made available. Use is_init_finished() and related functions
           instead.

           Returns the SSL connection state.

               my $rv = Net::SSLeay::get_state($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: (integer) state value
               #          to decode the returned state check:
               #          SSL_ST_* constants in openssl/ssl.h
               #          SSL2_ST_* constants in openssl/ssl2.h
               #          SSL23_ST_* constants in openssl/ssl23.h
               #          SSL3_ST_* + DTLS1_ST_* constants in openssl/ssl3.h

       •   state

           Exactly the same as "get_state".

               my $rv = Net::SSLeay::state($ssl);

       •   set_state

           Sets the SSL connection state.

               Net::SSLeay::set_state($ssl,Net::SSLeay::SSL_ST_ACCEPT());

           Not available with OpenSSL 1.1 and later.

       •   get_verify_depth

           Returns the verification depth limit currently set in $ssl.

               my $rv = Net::SSLeay::get_verify_depth($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: current depth or -1 if no limit has been explicitly set

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_verify_mode.html>

       •   set_verify_depth

           Sets  the  maximum depth for the certificate chain verification that
           shall be allowed for $ssl.

               Net::SSLeay::set_verify_depth($ssl, $depth);
               # $ssl - value corresponding to openssl's SSL structure
               # $depth - (integer) depth
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_verify.html>

       •   get_verify_mode

           Returns the verification mode (bitmask) currently set in $ssl.

               my $rv = Net::SSLeay::get_verify_mode($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: mode (bitmask)

           To   decode   the  return  value  (bitmask)  see  documentation  for
           "CTX_get_verify_mode".

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_verify_mode.html>

       •   set_verify

           Sets  the  verification flags for $ssl to be $mode and specifies the
           $verify_callback function to be used.

               Net::SSLeay::set_verify($ssl, $mode, $callback);
               # $ssl - value corresponding to openssl's SSL structure
               # $mode - mode (bitmask)
               # $callback - [optional] reference to perl callback function
               #
               # returns: no return value

           For $mode bitmask details see "CTX_get_verify_mode".

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_verify.html>

       •   set_post_handshake_auth

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at least OpenSSL 1.1.1, not in LibreSSL

           Enable  the  Post-Handshake  Authentication extension to be added to
           the ClientHello  such  that  post-handshake  authentication  can  be
           requested by the server.

               Net::SSLeay::set_posthandshake_auth($ssl, $val);
               # $ssl - value corresponding to openssl's SSL structure
               # $val - 0 then the extension is not sent, otherwise it is
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_post_handshake_auth.html>

       •   verify_client_post_handshake

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at least OpenSSL 1.1.1, not in LibreSSL

           verify_client_post_handshake causes a CertificateRequest message  to
           be sent by a server on the given ssl connection.

               my $rv = Net::SSLeay::verify_client_post_handshake($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: 1 if the request succeeded, and 0 if the request failed. The error stack can be examined to determine the failure reason.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_verify_client_post_handshake.html>

       •   get_verify_result

           Returns the result of  the  verification  of  the  X509  certificate
           presented by the peer, if any.

               my $rv = Net::SSLeay::get_verify_result($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: (integer)
               #      0 - X509_V_OK: ok
               #      2 - X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT: unable to get issuer certificate
               #      3 - X509_V_ERR_UNABLE_TO_GET_CRL: unable to get certificate CRL
               #      4 - X509_V_ERR_UNABLE_TO_DECRYPT_CERT_SIGNATURE: unable to decrypt certificate's signature
               #      5 - X509_V_ERR_UNABLE_TO_DECRYPT_CRL_SIGNATURE: unable to decrypt CRL's signature
               #      6 - X509_V_ERR_UNABLE_TO_DECODE_ISSUER_PUBLIC_KEY: unable to decode issuer public key
               #      7 - X509_V_ERR_CERT_SIGNATURE_FAILURE: certificate signature failure
               #      8 - X509_V_ERR_CRL_SIGNATURE_FAILURE: CRL signature failure
               #      9 - X509_V_ERR_CERT_NOT_YET_VALID: certificate is not yet valid
               #     10 - X509_V_ERR_CERT_HAS_EXPIRED: certificate has expired
               #     11 - X509_V_ERR_CRL_NOT_YET_VALID: CRL is not yet valid
               #     12 - X509_V_ERR_CRL_HAS_EXPIRED: CRL has expired
               #     13 - X509_V_ERR_ERROR_IN_CERT_NOT_BEFORE_FIELD: format error in certificate's notBefore field
               #     14 - X509_V_ERR_ERROR_IN_CERT_NOT_AFTER_FIELD: format error in certificate's notAfter field
               #     15 - X509_V_ERR_ERROR_IN_CRL_LAST_UPDATE_FIELD: format error in CRL's lastUpdate field
               #     16 - X509_V_ERR_ERROR_IN_CRL_NEXT_UPDATE_FIELD: format error in CRL's nextUpdate field
               #     17 - X509_V_ERR_OUT_OF_MEM: out of memory
               #     18 - X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT: self signed certificate
               #     19 - X509_V_ERR_SELF_SIGNED_CERT_IN_CHAIN: self signed certificate in certificate chain
               #     20 - X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY: unable to get local issuer certificate
               #     21 - X509_V_ERR_UNABLE_TO_VERIFY_LEAF_SIGNATURE: unable to verify the first certificate
               #     22 - X509_V_ERR_CERT_CHAIN_TOO_LONG: certificate chain too long
               #     23 - X509_V_ERR_CERT_REVOKED: certificate revoked
               #     24 - X509_V_ERR_INVALID_CA: invalid CA certificate
               #     25 - X509_V_ERR_PATH_LENGTH_EXCEEDED: path length constraint exceeded
               #     26 - X509_V_ERR_INVALID_PURPOSE: unsupported certificate purpose
               #     27 - X509_V_ERR_CERT_UNTRUSTED: certificate not trusted
               #     28 - X509_V_ERR_CERT_REJECTED: certificate rejected
               #     29 - X509_V_ERR_SUBJECT_ISSUER_MISMATCH: subject issuer mismatch
               #     30 - X509_V_ERR_AKID_SKID_MISMATCH: authority and subject key identifier mismatch
               #     31 - X509_V_ERR_AKID_ISSUER_SERIAL_MISMATCH: authority and issuer serial number mismatch
               #     32 - X509_V_ERR_KEYUSAGE_NO_CERTSIGN:key usage does not include certificate signing
               #     50 - X509_V_ERR_APPLICATION_VERIFICATION: application verification failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_verify_result.html>

       •   set_verify_result

           Override result of peer certificate verification.

               Net::SSLeay::set_verify_result($ssl, $v);
               # $ssl - value corresponding to openssl's SSL structure
               # $v - (integer) result value
               #
               # returns: no return value

           For more info about valid return values see "get_verify_result"

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_verify_result.html>

       •   get_wbio

           Get 'write' BIO linked to an SSL object $ssl.

               my $rv = Net::SSLeay::get_wbio($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: value corresponding to openssl's BIO structure (0 on failure)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_rbio.html>

       •   load_client_CA_file

           Load X509 certificates from file (PEM formatted).

               my $rv = Net::SSLeay::load_client_CA_file($file);
               # $file - (string) file name
               #
               # returns: value corresponding to openssl's STACK_OF(X509_NAME) structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_load_client_CA_file.html>

       •   clear_num_renegotiations

           Executes SSL_CTRL_CLEAR_NUM_RENEGOTIATIONS command on $ssl.

               my $rv = Net::SSLeay::clear_num_renegotiations($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: command result

       •   need_tmp_RSA

           Executes SSL_CTRL_NEED_TMP_RSA command on $ssl.

               my $rv = Net::SSLeay::need_tmp_RSA($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: command result

           Not available with OpenSSL 1.1 and later.

       •   num_renegotiations

           Executes SSL_CTRL_GET_NUM_RENEGOTIATIONS command on $ssl.

               my $rv = Net::SSLeay::num_renegotiations($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: command result

       •   total_renegotiations

           Executes SSL_CTRL_GET_TOTAL_RENEGOTIATIONS command on $ssl.

               my $rv = Net::SSLeay::total_renegotiations($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: command result

       •   peek

           Copies  $max  bytes from the specified $ssl into the returned value.
           In contrast to the Net::SSLeay::read() function, the data in the SSL
           buffer is unmodified after the SSL_peek() operation.

               Net::SSLeay::peek($ssl, $max);
               # $ssl - value corresponding to openssl's SSL structure
               # $max - [optional] max bytes to peek (integer) - default is 32768
               #
               # in scalar context: data read from the TLS/SSL connection, undef on error
               # in list context:   two-item array consisting of data read (undef on error),
               #                      and return code from SSL_peek().

       •   peek_ex

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at least OpenSSL 1.1.1, not in LibreSSL

           Copies $max bytes from the specified $ssl into the  returned  value.
           In  contrast to the Net::SSLeay::read_ex() function, the data in the
           SSL buffer is unmodified after the SSL_peek_ex() operation.

               my($got, $rv) = Net::SSLeay::peek_ex($ssl, $max);
               # $ssl - value corresponding to openssl's SSL structure
               # $max - [optional] max bytes to peek (integer) - default is 32768
               #
               # returns a list: two-item list consisting of data read (undef on error),
               #                 and return code from SSL_peek_ex().

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_peek_ex.html>

       •   pending

           Obtain number of readable bytes buffered in $ssl object.

               my $rv = Net::SSLeay::pending($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: the number of bytes pending

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_pending.html>

       •   has_pending

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at least OpenSSL 1.1.0, not in LibreSSL

           Returns  1  if  $ssl  has  buffered  data  (whether   processed   or
           unprocessed) and 0 otherwise.

               my $rv = Net::SSLeay::has_pending($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: (integer) 1 or 0

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_has_pending.html>

       •   read

           Tries to read $max bytes from the specified $ssl.

               my $got = Net::SSLeay::read($ssl, $max);
               my($got, $rv) = Net::SSLeay::read($ssl, $max);
               # $ssl - value corresponding to openssl's SSL structure
               # $max - [optional] max bytes to read (integer) - default is 32768
               #
               # returns:
               # in scalar context: data read from the TLS/SSL connection, undef on error
               # in list context:   two-item array consisting of data read (undef on error),
               #                      and return code from SSL_read().

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_read.html>

       •   read_ex

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at least OpenSSL 1.1.1, not in LibreSSL

           Tries to read $max bytes from the specified $ssl.

               my($got, $rv) = Net::SSLeay::read_ex($ssl, $max);
               # $ssl - value corresponding to openssl's SSL structure
               # $max - [optional] max bytes to read (integer) - default is 32768
               #
               # returns a list: two-item list consisting of data read (undef on error),
               #                 and return code from SSL_read_ex().

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_read_ex.html>

       •   renegotiate

           Turn on flags for renegotiation so that renegotiation will happen

               my $rv = Net::SSLeay::renegotiate($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: 1 on success, 0 on failure

       •   rstate_string

           Returns a 2 letter string indicating the current read state  of  the
           SSL object $ssl.

               my $rv = Net::SSLeay::rstate_string($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: 2-letter string

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_rstate_string.html>

       •   rstate_string_long

           Returns a string indicating the current read state of the SSL object
           ssl.

               my $rv = Net::SSLeay::rstate_string_long($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: string with current state

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_rstate_string.html>

       •   session_reused

           Query whether a reused session was negotiated during handshake.

               my $rv = Net::SSLeay::session_reused($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: 0 - new session was negotiated; 1 - session was reused.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_session_reused.html>

       •   set1_param

           COMPATIBILITY: requires at least OpenSSL 1.0.0-beta3

           Applies X509 verification parameters $vpm on $ssl

               my $rv = Net::SSLeay::set1_param($ssl, $vpm);
               # $ssl - value corresponding to openssl's SSL structure
               # $vpm - value corresponding to openssl's X509_VERIFY_PARAM structure
               #
               # returns: 1 on success, 0 on failure

       •   set_accept_state

           Sets $ssl to work in server mode.

               Net::SSLeay::set_accept_state($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_connect_state.html>

       •   set_bio

           Connects  the BIOs $rbio and $wbio for the read and write operations
           of the TLS/SSL (encrypted) side of $ssl.

               Net::SSLeay::set_bio($ssl, $rbio, $wbio);
               # $ssl - value corresponding to openssl's SSL structure
               # $rbio - value corresponding to openssl's BIO structure
               # $wbio - value corresponding to openssl's BIO structure
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_bio.html>

       •   set_cipher_list

           Sets the list of ciphers only for ssl.

               my $rv = Net::SSLeay::set_cipher_list($ssl, $str);
               # $ssl - value corresponding to openssl's SSL structure
               # $str - (string) cipher list e.g. '3DES:+RSA'
               #
               # returns: 1 if any cipher could be selected and 0 on complete failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_cipher_list.html>

       •   set_ciphersuites

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at  least  OpenSSL  1.1.1   or   at   least   LibreSSL   3.4.0   and
           Net-SSLeay-1.94

           Configure the available TLSv1.3 ciphersuites.

               my $rv = Net::SSLeay::set_ciphersuites($ssl, $str);
               # $ssl  - value corresponding to openssl's SSL structure
               # $str  - colon (":") separated list of TLSv1.3 ciphersuite names in order of preference
               #
               # returns: (integer) 1 if the requested ciphersuite list was configured, and 0 otherwise

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_ciphersuites.html>

       •   set_client_CA_list

           Sets the list of CAs sent to the client  when  requesting  a  client
           certificate  for  the  chosen $ssl, overriding the setting valid for
           $ssl's SSL_CTX object.

               my $rv = Net::SSLeay::set_client_CA_list($ssl, $list);
               # $ssl - value corresponding to openssl's SSL structure
               # $list - value corresponding to openssl's STACK_OF(X509_NAME) structure
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_client_CA_list.html>

       •   set_connect_state

           Sets $ssl to work in client mode.

               Net::SSLeay::set_connect_state($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_connect_state.html>

       •   set_fd

           Sets the file descriptor $fd as the input/output  facility  for  the
           TLS/SSL  (encrypted)  side of $ssl, $fd will typically be the socket
           file descriptor of a network connection.

               my $rv = Net::SSLeay::set_fd($ssl, $fd);
               # $ssl - value corresponding to openssl's SSL structure
               # $fd - (integer) file handle (got via perl's fileno)
               #
               # returns: 1 on success, 0 on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_fd.html>

       •   set_psk_client_callback

           Sets the psk client callback.

               Net::SSLeay::set_psk_client_callback($ssl, sub { my $hint = shift; return ($identity, $key) } );
               # $ssl - value corresponding to openssl's SSL structure
               # $hint - PSK identity hint send by the server
               # $identity - PSK identity
               # $key - PSK key, hex string without the leading '0x', e.g. 'deadbeef'
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_psk_client_callback.html>

       •   set_rfd

           Sets the file descriptor $fd as the input (read)  facility  for  the
           TLS/SSL (encrypted) side of $ssl.

               my $rv = Net::SSLeay::set_rfd($ssl, $fd);
               # $ssl - value corresponding to openssl's SSL structure
               # $fd - (integer) file handle (got via perl's fileno)
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_fd.html>

       •   set_wfd

               my $rv = Net::SSLeay::set_wfd($ssl, $fd);
               # $ssl - value corresponding to openssl's SSL structure
               # $fd - (integer) file handle (got via perl's fileno)
               #
               # returns: 1 on success, 0 on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_fd.html>

       •   set_info_callback

           Sets  the  callback  function,  that  can  be  used  to obtain state
           information for $ssl during connection setup and use.  When callback
           is undef, the callback setting currently valid for ctx is used.

               Net::SSLeay::set_info_callback($ssl, $cb, [$data]);
               # $ssl - value corresponding to openssl's SSL structure
               # $cb - sub { my ($ssl,$where,$ret,$data) = @_; ... }
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_info_callback.html>

       •   CTX_set_info_callback

           Sets  the callback function on ctx, that can be used to obtain state
           information during ssl connection setup and use.  When  callback  is
           undef, an existing callback will be disabled.

               Net::SSLeay::CTX_set_info_callback($ssl, $cb, [$data]);
               # $ssl - value corresponding to openssl's SSL structure
               # $cb - sub { my ($ssl,$where,$ret,$data) = @_; ... }
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_info_callback.html>

       •   set_msg_callback

           Sets the callback function, that can  be  used  to  obtain  protocol
           messages information for $ssl during connection setup and use.  When
           callback  is  undef, the callback setting currently valid for ctx is
           used.  Note that set_msg_callback_arg is not provided as there is no
           need to explicitly set $arg, this is handled by set_msg_callback.

               Net::SSLeay::set_msg_callback($ssl, $cb, [$arg]);
               # $ssl - value corresponding to openssl's SSL structure
               # $cb - sub { my ($write_p,$version,$content_type,$buf,$len,$ssl,$arg) = @_; ... }
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_msg_callback.html>

       •   CTX_set_msg_callback

           Sets  the  callback  function  on  ctx,  that  can be used to obtain
           protocol messages information for  ssl  connection  setup  and  use.
           When  callback  is  undef,  the  existing callback will be disabled.
           Note that CTX_set_msg_callback_arg is not provided as  there  is  no
           need    to    explicitly    set    $arg,    this   is   handled   by
           CTX_set_msg_callback.

               Net::SSLeay::CTX_set_msg_callback($ssl, $cb, [$arg]);
               # $ssl - value corresponding to openssl's SSL structure
               # $cb - sub { my ($write_p,$version,$content_type,$buf,$len,$ssl,$arg) = @_; ... }
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_msg_callback.html>

       •   set_pref_cipher

           Sets the list of available ciphers for $ssl using the control string
           $str.

               my $rv = Net::SSLeay::set_pref_cipher($ssl, $str);
               # $ssl - value corresponding to openssl's SSL structure
               # $str - (string) cipher list e.g. '3DES:+RSA'
               #
               # returns: 1 if any cipher could be selected and 0 on complete failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_cipher_list.html>

       •   CTX_set_psk_client_callback

           Sets the psk client callback.

               Net::SSLeay::CTX_set_psk_client_callback($ssl, sub { my $hint = shift; return ($identity, $key) } );
               # $ssl - value corresponding to openssl's SSL structure
               # $hint - PSK identity hint send by the server
               # $identity - PSK identity
               # $key - PSK key, hex string without the leading '0x', e.g. 'deadbeef'
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_psk_client_callback.html>

       •   set_purpose

               my $rv = Net::SSLeay::set_purpose($ssl, $purpose);
               # $ssl - value corresponding to openssl's SSL structure
               # $purpose - (integer) purpose identifier
               #
               # returns: 1 on success, 0 on failure

           For   more   info   about   available   $purpose   identifiers   see
           "CTX_set_purpose".

       •   set_quiet_shutdown

           Sets the 'quiet shutdown' flag for $ssl to be $mode.

               Net::SSLeay::set_quiet_shutdown($ssl, $mode);
               # $ssl - value corresponding to openssl's SSL structure
               # $mode - 0 or 1
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_quiet_shutdown.html>

       •   set_session

           Set a TLS/SSL session to be used during TLS/SSL connect.

               my $rv = Net::SSLeay::set_session($to, $ses);
               # $to - value corresponding to openssl's SSL structure
               # $ses - value corresponding to openssl's SSL_SESSION structure
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_session.html>

       •   set_session_id_context

           Sets the context $sid_ctx of  length  $sid_ctx_len  within  which  a
           session can be reused for the $ssl object.

               my $rv = Net::SSLeay::set_session_id_context($ssl, $sid_ctx, $sid_ctx_len);
               # $ssl - value corresponding to openssl's SSL structure
               # $sid_ctx - data buffer
               # $sid_ctx_len - length of data in $sid_ctx
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_session_id_context.html>

       •   set_session_secret_cb

           Setup pre-shared secret session resumption function.

               Net::SSLeay::set_session_secret_cb($ssl, $func, $data);
               # $ssl - value corresponding to openssl's SSL structure
               # $func - perl reference to callback function
               # $data - [optional] data that will be passed to callback function when invoked
               #
               # returns: no return value

           The callback function will be called like:

               callback_function($secret, $ciphers, $pref_cipher, $data);
               # $secret is the current master session key, usually all 0s at the beginning of a session
               # $ciphers is ref to an array of peer cipher names
               # $pref_cipher is a ref to an index into the list of cipher names of
               #  the preferred cipher. Set it if you want to specify a preferred cipher
               # $data is the data passed to set_session_secret_cb

           The callback function should return 1  if  it  likes  the  suggested
           cipher (or has selected an alternative by setting pref_cipher), else
           it  should  return  0  (in  which  case  OpenSSL will select its own
           preferred cipher).

           With OpenSSL 1.1 and later, callback_function can change the  master
           key for the session by altering $secret and returning 1.

       •   CTX_set_tlsext_ticket_getkey_cb

           Setup encryption for TLS session tickets (stateless session reuse).

               Net::SSLeay::CTX_set_tlsext_ticket_getkey_cb($ctx, $func, $data);
               # $ctx  - value corresponding to openssl's SSL_CTX structure
               # $func - perl reference to callback function
               # $data - [optional] data that will be passed to callback function when invoked
               #
               # returns: no return value

           The callback function will be called like:

               getkey($data,[$key_name]) -> ($key,$current_key_name)
               # $data is the data passed to set_session_secret_cb
               # $key_name is the name of the key OpenSSL has extracted from the session ticket
               # $key is the requested key for ticket encryption + HMAC
               # $current_key_name is the name for the currently valid key

           OpenSSL  will call the function without a key name if it generates a
           new  ticket.   It  then   needs   the   callback   to   return   the
           encryption+HMAC key and an identifier (key name) for this key.

           When  OpenSSL  gets a session ticket from the client it extracts the
           key name and calls the callback with this name as argument. It  then
           expects  the callback to return the encryption+HMAC key matching the
           requested key name and and also the key name which should be used at
           the moment. If the requested key name  and  the  returned  key  name
           differ it means that this session ticket was created with an expired
           key  and  need  to  be  renewed.  In this case OpenSSL will call the
           callback again with no key name to create a new session ticket based
           on the old one.

           The key must be at least 32 byte of random data which can be created
           with RAND_bytes. Internally the first 16 byte are  used  as  key  in
           AES-128  encryption  while the next 16 byte are used for the SHA-256
           HMAC.  The key name are binary data and  must  be  exactly  16  byte
           long.

           Example:

               Net::SSLeay::RAND_bytes(my $oldkey,32);
               Net::SSLeay::RAND_bytes(my $newkey,32);
               my $oldkey_name = pack("a16",'oldsecret');
               my $newkey_name = pack("a16",'newsecret');

               my @keys = (
                   [ $newkey_name, $newkey ], # current active key
                   [ $oldkey_name, $oldkey ], # already expired
               );

               Net::SSLeay::CTX_set_tlsext_ticket_getkey_cb($server2->_ctx, sub {
                   my ($mykeys,$name) = @_;

                   # return (current_key, current_key_name) if no name given
                   return ($mykeys->[0][1],$mykeys->[0][0]) if ! $name;

                   # return (matching_key, current_key_name) if we find a key matching
                   # the given name
                   for(my $i = 0; $i<@$mykeys; $i++) {
                       next if $name ne $mykeys->[$i][0];
                       return ($mykeys->[$i][1],$mykeys->[0][0]);
                   }

                   # no matching key found
                   return;
               },\@keys);

           This     function    is    based    on    the    OpenSSL    function
           SSL_CTX_set_tlsext_ticket_key_cb  but  provides  a  simpler  to  use
           interface.          For         more         information         see
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_tlsext_ticket_key_cb.html>

       •   set_session_ticket_ext_cb

           Setup callback for TLS session tickets (stateless session reuse).

               Net::SSLeay::set_session_ticket_ext_cb($ssl, $func, $data);
               # $ssl  - value corresponding to openssl's SSL structure
               # $func - perl reference to callback function
               # $data - [optional] data that will be passed to callback function when invoked
               #
               # returns: no return value

           The callback function will be called like:

               getticket($ssl,$ticket,$data) -> $return_value
               # $ssl is a value corresponding to openssl's SSL structure
               # $ticket is a value of received TLS session ticket (can also be empty)
               # $data is the data passed to set_session_ticket_ext_cb
               # $return_value is either 0 (failure) or 1 (success)

           This    function    is    based    on    the    OpenSSL     function
           SSL_set_session_ticket_ext_cb.

       •   set_session_ticket_ext

           Set TLS session ticket (stateless session reuse).

               Net::SSLeay::set_session_ticket_ext($ssl, $ticket);
               # $ssl    - value corresponding to openssl's SSL structure
               # $ticket - is a value of TLS session ticket which client will send (can also be empty string)
               #
               # returns: no return value

           The callback function will be called like:

               getticket($ssl,$ticket,$data) -> $return_value
               # $ssl is a value corresponding to openssl's SSL structure
               # $ticket is a value of received TLS session ticket (can also be empty)
               # $data is the data passed to set_session_ticket_ext_cb
               # $return_value is either 0 (failure) or 1 (success)

           This     function    is    based    on    the    OpenSSL    function
           SSL_set_session_ticket_ext_cb.

       •   set_shutdown

           Sets the shutdown state of $ssl to $mode.

               Net::SSLeay::set_shutdown($ssl, $mode);
               # $ssl - value corresponding to openssl's SSL structure
               # $mode - (integer) shutdown mode:
               #         0 - No shutdown
               #         1 - SSL_SENT_SHUTDOWN
               #         2 - SSL_RECEIVED_SHUTDOWN
               #         3 - SSL_RECEIVED_SHUTDOWN+SSL_SENT_SHUTDOWN
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_shutdown.html>

       •   set_ssl_method

           Sets a new TLS/SSL method for a particular $ssl object.

               my $rv = Net::SSLeay::set_ssl_method($ssl, $method);
               # $ssl - value corresponding to openssl's SSL structure
               # $method - value corresponding to openssl's SSL_METHOD structure
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_ssl_version.html>

       •   set_tmp_dh

           Sets DH parameters to be used to be $dh.

               my $rv = Net::SSLeay::set_tmp_dh($ssl, $dh);
               # $ssl - value corresponding to openssl's SSL structure
               # $dh - value corresponding to openssl's DH structure
               #
               # returns: 1 on success, 0 on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_tmp_dh_callback.html>

       •   set_tmp_dh_callback

           Sets  the callback function for $ssl to be used when a DH parameters
           are required to $dh_cb.

           ??? (does this function really work?)

               Net::SSLeay::set_tmp_dh_callback($ssl, $dh);
               # $ssl - value corresponding to openssl's SSL structure
               # $dh_cb - pointer to function ???
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_tmp_dh_callback.html>

       •   set_tmp_rsa

           Sets the temporary/ephemeral RSA key to be used in $ssl to be $rsa.

               my $rv = Net::SSLeay::set_tmp_rsa($ssl, $rsa);
               # $ssl - value corresponding to openssl's SSL structure
               # $rsa - value corresponding to openssl's RSA structure
               #
               # returns: 1 on success, 0 on failure

           Example:

               $rsakey = Net::SSLeay::RSA_generate_key();
               Net::SSLeay::set_tmp_rsa($ssl, $rsakey);
               Net::SSLeay::RSA_free($rsakey);

           Check                           openssl                          doc
           <https://www.openssl.org/docs/man1.0.2/man3/SSL_CTX_set_tmp_rsa_callback.html>

       •   set_tmp_rsa_callback

           Sets  the  callback  function  for  $ssl   to   be   used   when   a
           temporary/ephemeral RSA key is required to $tmp_rsa_callback.

           ??? (does this function really work?)

               Net::SSLeay::set_tmp_rsa_callback($ssl, $tmp_rsa_callback);
               # $ssl - value corresponding to openssl's SSL structure
               # $tmp_rsa_callback - (function pointer) ???
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/man1.0.2/man3/SSL_CTX_set_tmp_rsa_callback.html>

       •   set_trust

               my $rv = Net::SSLeay::set_trust($ssl, $trust);
               # $ssl - value corresponding to openssl's SSL structure
               # $trust - (integer) trust identifier
               #
               # returns: the original value

           For more details about $trust values see "CTX_set_trust".

       •   shutdown

           Shuts down an active TLS/SSL connection. It sends the 'close notify'
           shutdown alert to the peer.

               my $rv = Net::SSLeay::shutdown($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: 1 - shutdown was successfully completed
               #          0 - shutdown is not yet finished,
               #         -1 - shutdown was not successful

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_shutdown.html>

       •   state_string

           Returns  a  6  letter string indicating the current state of the SSL
           object $ssl.

               my $rv = Net::SSLeay::state_string($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: 6-letter string

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_state_string.html>

       •   state_string_long

           Returns  a  string  indicating  the  current state of the SSL object
           $ssl.

               my $rv = Net::SSLeay::state_string_long($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: state strings

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_state_string.html>

       •   set_default_passwd_cb

           COMPATIBILITY: not available in Net-SSLeay-1.82 and before; requires
           at least OpenSSL 1.1.0f. Not needed with LibreSSL.

           Sets the default password callback called when loading/storing a PEM
           certificate with encryption for $ssl.

               Net::SSLeay::set_default_passwd_cb($ssl, $func);
               # $ssl - value corresponding to openssl's SSL structure
               # $func - perl reference to callback function
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_default_passwd_cb.html>

       •   set_default_passwd_cb_userdata

           COMPATIBILITY: not available in Net-SSLeay-1.82 and before; requires
           at least OpenSSL 1.1.0f. Not needed with LibreSSL.

           Sets a pointer to userdata which will be provided  to  the  password
           callback of $ssl on invocation.

               Net::SSLeay::set_default_passwd_cb_userdata($ssl, $userdata);
               # $ssl - value corresponding to openssl's SSL structure
               # $userdata - data that will be passed to callback function when invoked
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_default_passwd_cb.html>

       •   use_PrivateKey

           Adds $pkey as private key to $ssl.

               my $rv = Net::SSLeay::use_PrivateKey($ssl, $pkey);
               # $ssl - value corresponding to openssl's SSL structure
               # $pkey - value corresponding to openssl's EVP_PKEY structure
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   use_PrivateKey_ASN1

           Adds the private key of type $pk stored in $data to $ssl.

               my $rv = Net::SSLeay::use_PrivateKey_ASN1($pk, $ssl, $d, $len);
               # $pk - (integer) key type, NID of corresponding algorithm
               # $ssl - value corresponding to openssl's SSL structure
               # $data - key data (binary)
               # $len - length of $data
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   use_PrivateKey_file

           Adds the first private key found in $file to $ssl.

               my $rv = Net::SSLeay::use_PrivateKey_file($ssl, $file, $type);
               # $ssl - value corresponding to openssl's SSL structure
               # $file - (string) file name
               # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   use_RSAPrivateKey

           Adds $rsa as RSA private key to $ssl.

               my $rv = Net::SSLeay::use_RSAPrivateKey($ssl, $rsa);
               # $ssl - value corresponding to openssl's SSL structure
               # $rsa - value corresponding to openssl's RSA structure
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   use_RSAPrivateKey_ASN1

           Adds RSA private key stored in $data to $ssl.

               my $rv = Net::SSLeay::use_RSAPrivateKey_ASN1($ssl, $data, $len);
               # $ssl - value corresponding to openssl's SSL structure
               # $data - key data (binary)
               # $len - length of $data
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   use_RSAPrivateKey_file

           Adds the first RSA private key found in $file to $ssl.

               my $rv = Net::SSLeay::use_RSAPrivateKey_file($ssl, $file, $type);
               # $ssl - value corresponding to openssl's SSL structure
               # $file - (string) file name
               # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   use_certificate

           Loads the certificate $x into $ssl.

               my $rv = Net::SSLeay::use_certificate($ssl, $x);
               # $ssl - value corresponding to openssl's SSL structure
               # $x - value corresponding to openssl's X509 structure
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   use_certificate_ASN1

           Loads the ASN1 encoded certificate from $data to $ssl.

               my $rv = Net::SSLeay::use_certificate_ASN1($ssl, $data, $len);
               # $ssl - value corresponding to openssl's SSL structure
               # $data - certificate data (binary)
               # $len - length of $data
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   use_certificate_chain_file

           COMPATIBILITY: not available in Net-SSLeay-1.82 and before; requires
           at  least  OpenSSL  1.1.0   or   at   least   LibreSSL   3.6.0   and
           Net-SSLeay-1.94

           Loads  a  certificate  chain  from $file into $ssl. The certificates
           must be in PEM format and must be sorted starting with the subject's
           certificate (actual  client  or  server  certificate),  followed  by
           intermediate  CA  certificates  if  applicable,  and  ending  at the
           highest level (root) CA.

               my $rv = Net::SSLeay::use_certificate_chain_file($ssl, $file);
               # $ssl - value corresponding to openssl's SSL structure
               # $file - (string) file name
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   use_certificate_file

           Loads the first certificate stored in $file into $ssl.

               my $rv = Net::SSLeay::use_certificate_file($ssl, $file, $type);
               # $ssl - value corresponding to openssl's SSL structure
               # $file - (string) file name
               # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
               #
               # returns: 1 on success, otherwise check out the error stack to find out the reason

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_certificate.html>

       •   get_version

           Returns SSL/TLS protocol name

               my $rv = Net::SSLeay::get_version($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: (string) protocol name, see OpenSSL manual for the full list
               #          TLSv1
               #          TLSv1.3

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_get_version.html>

       •   version

           Returns SSL/TLS protocol version

               my $rv = Net::SSLeay::version($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: (integer) protocol version, see OpenSSL manual for the full list
               #          0x0301 - TLS1_VERSION  (TLSv1)
               #          0xFEFF - DTLS1_VERSION (DTLSv1)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_version.html>

       •   client_version

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at least OpenSSL 1.1.0, not in LibreSSL

           Returns TLS protocol version used by the client when initiating  the
           connection

               my $rv = Net::SSLeay::client_version($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: (integer) protocol version, see OpenSSL manual for the full list
               #          0x0301 - TLS1_VERSION  (TLSv1)
               #          0xFEFF - DTLS1_VERSION (DTLSv1)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_client_version.html>

       •   is_dtls

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at  least  OpenSSL  1.1.0   or   at   least   LibreSSL   3.3.1   and
           Net-SSLeay-1.94

               my $rv = Net::SSLeay::is_dtls($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: (integer) zero or one
               #          0 - connection is not using DTLS
               #          1 - connection is using DTLS

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_is_dtls.html>

       •   want

           Returns state information for the SSL object $ssl.

               my $rv = Net::SSLeay::want($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: state
               #          1 - SSL_NOTHING
               #          2 - SSL_WRITING
               #          3 - SSL_READING
               #          4 - SSL_X509_LOOKUP

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_want.html>

       •   write

           Writes   data   from  the  buffer  $data  into  the  specified  $ssl
           connection.

               my $rv = Net::SSLeay::write($ssl, $data);
               # $ssl - value corresponding to openssl's SSL structure
               # $data - data to be written
               #
               # returns: >0 - (success) number of bytes actually written to the TLS/SSL connection
               #           0 - write not successful, probably the underlying connection was closed
               #          <0 - error

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_write.html>

       •   write_ex

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at least OpenSSL 1.1.1, not in LibreSSL

           Writes   data   from  the  buffer  $data  into  the  specified  $ssl
           connection.

               my ($len, $rv) = Net::SSLeay::write_ex($ssl, $data);
               # $ssl - value corresponding to openssl's SSL structure
               # $data - data to be written
               #
               # returns a list: two-item list consisting of number of bytes written,
               #                 and return code from SSL_write_ex()

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_write_ex.html>

       •   write_partial

           NOTE: Does not exactly correspond to any low level API function

           Writes  a  fragment  of data in $data from the buffer $data into the
           specified $ssl connection. This  is  a  non-blocking  function  like
           Net::SSLeay::write().

               my $rv = Net::SSLeay::write_partial($ssl, $from, $count, $data);
               # $ssl - value corresponding to openssl's SSL structure
               # $from - (integer) offset from the beginning of $data
               # $count - (integer) length of data to be written
               # $data - data buffer
               #
               # returns: >0 - (success) number of bytes actually written to the TLS/SSL connection
               #           0 - write not successful, probably the underlying connection was closed
               #          <0 - error

       •   set_tlsext_host_name

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before; requires
           at least OpenSSL 0.9.8f

           Sets TLS servername extension on SSL object $ssl to value $name.

               my $rv = set_tlsext_host_name($ssl, $name);
               # $ssl - value corresponding to openssl's SSL structure
               # $name - (string) name to be set
               #
               # returns: 1 on success, 0 on failure

       •   client_hello_isv2

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.1pre1, not in LibreSSL

           NOTE:    to    be    used    only   from   a   callback   set   with
           CTX_set_client_hello_cb.

           Indicate if the ClientHello was carried in a SSLv2 record and is  in
           the SSLv2 format.

               my $rv = client_hello_isv2($s);
               # $s - value corresponding to openssl's SSL structure
               #
               # returns: 1 for SSLv2-format ClientHellos and 0 otherwise

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_client_hello_isv2.html>

       •   client_hello_get0_legacy_version

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.1pre1, not in LibreSSL

           NOTE:   to   be   used   only   from    a    callback    set    with
           CTX_set_client_hello_cb.

           Returns legacy_version, also known as client_version, field from the
           ClientHello.

               my $rv = client_hello_get0_legacy_version($s);
               # $s - value corresponding to openssl's SSL structure
               #
               # returns: unsigned integer, for example 0x0303 (TLS v1.2) with TLS 1.3

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_client_hello_get0_legacy_version.html>

       •   client_hello_get0_random,              client_hello_get0_session_id,
           client_hello_get0_ciphers and client_hello_get0_compression_methods

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.1pre1, not in LibreSSL

           NOTE:    to    be    used    only   from   a   callback   set   with
           CTX_set_client_hello_cb.

           These  functions  return  random,  session_id,   cipher_suites   and
           compression_methods fields from the ClientHello, respectively.

               my $random = client_hello_get0_random($s);
               my $session_id = client_hello_get0_session_id($s);
               my $ciphers = client_hello_get0_ciphers($s);
               my $compression_methods = client_hello_get0_compression_methods($s);
               # $s - value corresponding to openssl's SSL structure
               #
               # returns: raw octet data where data length, zero or more, depends on the field definition

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_client_hello_get0_random.html>

       •   client_hello_get1_extensions_present                             and
           client_hello_get_extension_order

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.1pre1, not in LibreSSL

           NOTE:    to    be    used    only   from   a   callback   set   with
           CTX_set_client_hello_cb.

           Returns a reference to an array holding the numerical value  of  the
           TLS  extension  types  in  the order they appear in the ClientHello.
           client_hello_get_extension_order is similar and  requires  at  least
           OpenSSL 3.2.0, not in LibreSSL.

               my $ref = client_hello_get1_extensions_present($s);
               # $s - value corresponding to openssl's SSL structure
               #
               # returns: an array reference of zero or more extension types or undef on failure

           Example from a TLS 1.3 ClientHello:

               sub client_hello_cb {
                   my ($ssl, $arg) = @_;
                   my $ref = client_hello_get1_extensions_present($ssl);
                   print join(' ', @$ref), "\n" if $ref;
               }

           Prints: "11 10 35 22 23 13 43 45 51"

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_client_hello_get1_extensions_present.html>

       •   client_hello_get0_ext

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.1pre1, not in LibreSSL

           NOTE:   to   be   used   only   from    a    callback    set    with
           CTX_set_client_hello_cb.

           Returns an extension by type number from the ClientHello.

               my $ref = client_hello_get1_extensions_present($s, $type);
               # $s - value corresponding to openssl's SSL structure
               # $type - (integer) extension type number
               #
               # returns: zero or more octets of extension contents including extension length, undef if the extension is not present

           Example:  Get  the  value of TLS extension "supported_versions". You
           can use constant "TLSEXT_TYPE_supported_versions" or 43 directly.

               sub client_hello_cb {
                   my ($ssl, $arg) = @_;
                   my $ext_ver = Net::SSLeay::client_hello_get0_ext($ssl, Net::SSLeay::TLSEXT_TYPE_supported_versions());
                   print unpack('H*', $ext_ver), "\n" if defined $ext_ver;
               }

           Prints:  080304030303020301  where  the  first  octet  0x08  is  the
           extension  length  and the following four 16bit values correspond to
           TLS versions 1.3, 1.2, 1.1 and 1.0.

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_client_hello_get0_ext.html>

       Low level API: RAND_* related functions

       Check       openssl       doc       related      to      RAND      stuff
       <https://www.openssl.org/docs/manmaster/man3/rand.html>

       •   RAND_add

           Mixes the $num bytes at $buf into the PRNG state.

               Net::SSLeay::RAND_add($buf, $num, $entropy);
               # $buf - buffer with data to be mixed into the PRNG state
               # $num - number of bytes in $buf
               # $entropy - estimate of how much randomness is contained in $buf (in bytes)
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/RAND_add.html>

       •   RAND_seed

           Equivalent to "RAND_add" when $num == $entropy.

               Net::SSLeay::RAND_seed($buf);   # Perlishly figures out buf size
               # $buf - buffer with data to be mixed into the PRNG state
               # $num - number of bytes in $buf
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/RAND_add.html>

       •   RAND_status

           Gives PRNG status (seeded enough or not).

               my $rv = Net::SSLeay::RAND_status();
               # returns: 1 if the PRNG has been seeded with enough data, 0 otherwise

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/RAND_add.html>

       •   RAND_bytes

           Puts $num cryptographically strong pseudo-random bytes into $buf.

               my $rv = Net::SSLeay::RAND_bytes($buf, $num);
               # $buf - buffer where the random data will be stored
               # $num - the size (in bytes) of requested random data
               #
               # returns: 1 on success, -1 if not supported by the current RAND method, or 0 on other failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/RAND_bytes.html>

       •   RAND_priv_bytes

           COMPATIBILITY: not available in Net-SSLeay-1.85 and before; requires
           at least OpenSSL 1.1.1, not in LibreSSL

           Puts $num cryptographically strong pseudo-random bytes into $buf.

               my $rv = Net::SSLeay::RAND_priv_bytes($buf, $num);
               # $buf - buffer where the random data will be stored
               # $num - the size (in bytes) of requested random data
               #
               # returns: 1 on success, -1 if not supported by the current RAND method, or 0 on other failure

           RAND_priv_bytes has the same semantics as RAND_bytes,  but  see  see
           the documentation for more information.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/RAND_priv_bytes.html>

       •   RAND_pseudo_bytes

           Puts $num pseudo-random (not necessarily unpredictable)  bytes  into
           $buf.

               my $rv = Net::SSLeay::RAND_pseudo_bytes($buf, $num);
               # $buf - buffer where the random data will be stored
               # $num - the size (in bytes) of requested random data
               #
               # returns: 1 if the bytes generated are cryptographically strong, 0 otherwise

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/RAND_bytes.html>

       •   RAND_cleanup

           Erase the PRNG state.

               Net::SSLeay::RAND_cleanup();
               # no args, no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/RAND_cleanup.html>

       •   RAND_egd_bytes

           Queries  the entropy gathering daemon EGD on socket $path for $bytes
           bytes.

               my $rv = Net::SSLeay::RAND_egd_bytes($path, $bytes);
               # $path - path to a socket of entropy gathering daemon EGD
               # $bytes - number of bytes we want from EGD
               #
               # returns: the number of bytes read from the daemon on success, and -1 on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/RAND_egd.html>

       •   RAND_file_name

           Generates a default path for the random seed file.

               my $file = Net::SSLeay::RAND_file_name($num);
               # $num - maximum size of returned file name
               #
               # returns: string with file name on success, '' (empty string) or undef on failure

           LibreSSL  and  OpenSSL  1.1.0a  and  later  return  undef  when, for
           example, $num is not large enough to hold the filename.

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/RAND_load_file.html>

       •   RAND_load_file

           COMPATIBILITY: Is no longer functional on LibreSSL

           Reads $max_bytes of bytes from $file_name and adds them to the PRNG.

               my $rv = Net::SSLeay::RAND_load_file($file_name, $max_bytes);
               # $file_name - the name of file
               # $max_bytes - bytes to read from $file_name; -1 => the complete file is read
               #
               # returns: the number of bytes read

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/RAND_load_file.html>

       •   RAND_write_file

           Writes 1024  random  bytes  to  $file_name  which  can  be  used  to
           initialize the PRNG by calling "RAND_load_file" in a later session.

               my $rv = Net::SSLeay::RAND_write_file($file_name);
               # $file_name - the name of file
               #
               # returns: the number of bytes written, and -1 if the bytes written were generated without appropriate seed

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/RAND_load_file.html>

       •   RAND_poll

           Collects some entropy from operating system and adds it to the PRNG.

               my $rv = Net::SSLeay::RAND_poll();
               # returns: 1 on success, 0 on failure (unable to gather reasonable entropy)

       Low level API: OBJ_* related functions

       •   OBJ_cmp

           Compares ASN1_OBJECT $a to ASN1_OBJECT $b.

               my $rv = Net::SSLeay::OBJ_cmp($a, $b);
               # $a - value corresponding to openssl's ASN1_OBJECT structure
               # $b - value corresponding to openssl's ASN1_OBJECT structure
               #
               # returns: if the two are identical 0 is returned

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/OBJ_nid2obj.html>

       •   OBJ_dup

           Returns a copy/duplicate of $o.

               my $rv = Net::SSLeay::OBJ_dup($o);
               # $o - value corresponding to openssl's ASN1_OBJECT structure
               #
               # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OBJ_nid2obj.html>

       •   OBJ_nid2ln

           Returns long name for given NID $n.

               my $rv = Net::SSLeay::OBJ_nid2ln($n);
               # $n - (integer) NID
               #
               # returns: (string) long name e.g. 'commonName'

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/OBJ_nid2obj.html>

       •   OBJ_ln2nid

           Returns NID corresponding to given long name $n.

               my $rv = Net::SSLeay::OBJ_ln2nid($s);
               # $s - (string) long name e.g. 'commonName'
               #
               # returns: (integer) NID

       •   OBJ_nid2sn

           Returns short name for given NID $n.

               my $rv = Net::SSLeay::OBJ_nid2sn($n);
               # $n - (integer) NID
               #
               # returns: (string) short name e.g. 'CN'

           Example:

               print Net::SSLeay::OBJ_nid2sn(&Net::SSLeay::NID_commonName);

       •   OBJ_sn2nid

           Returns NID corresponding to given short name $s.

               my $rv = Net::SSLeay::OBJ_sn2nid($s);
               # $s - (string) short name e.g. 'CN'
               #
               # returns: (integer) NID

           Example:

               print "NID_commonName constant=", &Net::SSLeay::NID_commonName;
               print "OBJ_sn2nid('CN')=", Net::SSLeay::OBJ_sn2nid('CN');

       •   OBJ_nid2obj

           Returns ASN1_OBJECT for given NID $n.

               my $rv = Net::SSLeay::OBJ_nid2obj($n);
               # $n - (integer) NID
               #
               # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OBJ_nid2obj.html>

       •   OBJ_obj2nid

           Returns NID corresponding to given ASN1_OBJECT $o.

               my $rv = Net::SSLeay::OBJ_obj2nid($o);
               # $o - value corresponding to openssl's ASN1_OBJECT structure
               #
               # returns: (integer) NID

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/OBJ_nid2obj.html>

       •   OBJ_txt2obj

           Converts  the  text  string  s  into  an  ASN1_OBJECT  structure. If
           $no_name is 0 then long names (e.g. 'commonName')  and  short  names
           (e.g.  'CN')  will  be  interpreted as well as numerical forms (e.g.
           '2.5.4.3'). If $no_name is 1 only the numerical form is acceptable.

               my $rv = Net::SSLeay::OBJ_txt2obj($s, $no_name);
               # $s - text string to be converted
               # $no_name - (integer) 0 or 1
               #
               # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/OBJ_nid2obj.html>

       •   OBJ_obj2txt

           Converts the ASN1_OBJECT a into a textual representation.

               Net::SSLeay::OBJ_obj2txt($a, $no_name);
               # $a - value corresponding to openssl's ASN1_OBJECT structure
               # $no_name - (integer) 0 or 1
               #
               # returns: textual representation e.g. 'commonName' ($no_name=0), '2.5.4.3' ($no_name=1)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OBJ_nid2obj.html>

       •   OBJ_txt2nid

           Returns NID corresponding to text string $s  which  can  be  a  long
           name, a short name or the numerical representation of an object.

               my $rv = Net::SSLeay::OBJ_txt2nid($s);
               # $s - (string) e.g. 'commonName' or 'CN' or '2.5.4.3'
               #
               # returns: (integer) NID

           Example:

               my $nid = Net::SSLeay::OBJ_txt2nid('2.5.4.3');
               Net::SSLeay::OBJ_nid2sn($n);

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OBJ_nid2obj.html>

       Low level API: ASN1_INTEGER_* related functions

       •   ASN1_INTEGER_new

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Creates a new ASN1_INTEGER structure.

               my $rv = Net::SSLeay::ASN1_INTEGER_new();
               #
               # returns: value corresponding to openssl's ASN1_INTEGER structure (0 on failure)

       •   ASN1_INTEGER_free

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Free an allocated ASN1_INTEGER structure.

               Net::SSLeay::ASN1_INTEGER_free($i);
               # $i - value corresponding to openssl's ASN1_INTEGER structure
               #
               # returns: no return value

       •   ASN1_INTEGER_get

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns integer value of given ASN1_INTEGER object.

           BEWARE: If the value stored in ASN1_INTEGER  is  greater  than  max.
           integer  that  can  be  stored in 'long' type (usually 32bit but may
           vary according to platform) then this function will return -1.   For
           getting     large     ASN1_INTEGER     values     consider     using
           "P_ASN1_INTEGER_get_dec" or "P_ASN1_INTEGER_get_hex".

               my $rv = Net::SSLeay::ASN1_INTEGER_get($a);
               # $a - value corresponding to openssl's ASN1_INTEGER structure
               #
               # returns: integer value of ASN1_INTEGER object in $a

       •   ASN1_INTEGER_set

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets value of given ASN1_INTEGER object to value $val

           BEWARE: $val has max. limit (= max. integer that can  be  stored  in
           'long'  type).  For setting large ASN1_INTEGER values consider using
           "P_ASN1_INTEGER_set_dec" or "P_ASN1_INTEGER_set_hex".

               my $rv = Net::SSLeay::ASN1_INTEGER_set($i, $val);
               # $i - value corresponding to openssl's ASN1_INTEGER structure
               # $val - integer value
               #
               # returns: 1 on success, 0 on failure

       •   P_ASN1_INTEGER_get_dec

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns string with decimal representation of integer value of given
           ASN1_INTEGER object.

               Net::SSLeay::P_ASN1_INTEGER_get_dec($i);
               # $i - value corresponding to openssl's ASN1_INTEGER structure
               #
               # returns: string with decimal representation

       •   P_ASN1_INTEGER_get_hex

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns string with hexadecimal representation of integer  value  of
           given ASN1_INTEGER object.

               Net::SSLeay::P_ASN1_INTEGER_get_hex($i);
               # $i - value corresponding to openssl's ASN1_INTEGER structure
               #
               # returns: string with hexadecimal representation

       •   P_ASN1_INTEGER_set_dec

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets  value  of  given  ASN1_INTEGER  object  to value $val (decimal
           string, suitable for large integers)

               Net::SSLeay::P_ASN1_INTEGER_set_dec($i, $str);
               # $i - value corresponding to openssl's ASN1_INTEGER structure
               # $str - string with decimal representation
               #
               # returns: 1 on success, 0 on failure

       •   P_ASN1_INTEGER_set_hex

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets value of given ASN1_INTEGER object to value  $val  (hexadecimal
           string, suitable for large integers)

               Net::SSLeay::P_ASN1_INTEGER_set_hex($i, $str);
               # $i - value corresponding to openssl's ASN1_INTEGER structure
               # $str - string with hexadecimal representation
               #
               # returns: 1 on success, 0 on failure

       Low level API: ASN1_STRING_* related functions

       •   P_ASN1_STRING_get

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns string value of given ASN1_STRING object.

               Net::SSLeay::P_ASN1_STRING_get($s, $utf8_decode);
               # $s - value corresponding to openssl's ASN1_STRING structure
               # $utf8_decode - [optional] 0 or 1 whether the returned value should be utf8 decoded (default=0)
               #
               # returns: string

               $string = Net::SSLeay::P_ASN1_STRING_get($s);
               # is the same as:
               $string = Net::SSLeay::P_ASN1_STRING_get($s, 0);

       Low level API: ASN1_TIME_* related functions

       •   ASN1_TIME_new

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

               my $time = ASN1_TIME_new();
               # returns: value corresponding to openssl's ASN1_TIME structure

       •   ASN1_TIME_free

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

               ASN1_TIME_free($time);
               # $time - value corresponding to openssl's ASN1_TIME structure

       •   ASN1_TIME_set

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

               ASN1_TIME_set($time, $t);
               # $time - value corresponding to openssl's ASN1_TIME structure
               # $t - time value in seconds since 1.1.1970

           BEWARE: It is platform dependent how this function will handle dates
           after  2038.   Although  perl's integer is large enough the internal
           implementation of this function is dependent on the size  of  time_t
           structure (32bit time_t has problem with 2038).

           If  you  want  to  safely  set date and time after 2038 use function
           "P_ASN1_TIME_set_isotime".

       •   P_ASN1_TIME_get_isotime

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

           NOTE: Does not exactly correspond to any low level API function

           Gives ISO-8601 string representation of ASN1_TIME structure.

               my $datetime_string = P_ASN1_TIME_get_isotime($time);
               # $time - value corresponding to openssl's ASN1_TIME structure
               #
               # returns: datetime string like '2033-05-16T20:39:37Z' or '' on failure

           The     output     format     is     compatible     with      module
           DateTime::Format::RFC3339

       •   P_ASN1_TIME_set_isotime

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

           NOTE: Does not exactly correspond to any low level API function

           Sets time and date value of ANS1_time structure.

               my $rv = P_ASN1_TIME_set_isotime($time, $string);
               # $time - value corresponding to openssl's ASN1_TIME structure
               # $string - ISO-8601 timedate string like '2033-05-16T20:39:37Z'
               #
               # returns: 1 on success, 0 on failure

           The    $string   parameter   has   to   be   in   full   form   like
           "2012-03-22T23:55:33"       or       "2012-03-22T23:55:33Z"       or
           "2012-03-22T23:55:33CET".  Short  forms  like  "2012-03-22T23:55" or
           "2012-03-22" are not supported.

       •   P_ASN1_TIME_put2string

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before, has bugs
           with OpenSSL 0.9.8i

           NOTE: Does not exactly correspond to any low level API function

           Gives string representation of ASN1_TIME structure.

               my $str = P_ASN1_TIME_put2string($time);
               # $time - value corresponding to openssl's ASN1_TIME structure
               #
               # returns: datetime string like 'May 16 20:39:37 2033 GMT'

       •   P_ASN1_UTCTIME_put2string

           NOTE: deprecated function, only for backward compatibility, just  an
           alias for "P_ASN1_TIME_put2string"

       Low level API: X509_* related functions

       •   X509_new

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Allocates and initializes a X509 structure.

               my $rv = Net::SSLeay::X509_new();
               #
               # returns: value corresponding to openssl's X509 structure (0 on failure)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_new.html>

       •   X509_free

           Frees up the X509 structure.

               Net::SSLeay::X509_free($a);
               # $a - value corresponding to openssl's X509 structure
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_new.html>

       •   X509_check_host

           COMPATIBILITY: not available in Net-SSLeay-1.68 and before; requires
           at least OpenSSL 1.0.2. X509_CHECK_FLAG_NEVER_CHECK_SUBJECT requires
           OpenSSL 1.1.0.

           Checks  if the certificate Subject Alternative Name (SAN) or Subject
           CommonName (CN) matches the specified host name.

               my $rv = Net::SSLeay::X509_check_host($cert, $name, $flags, $peername);
               # $cert - value corresponding to openssl's X509 structure
               # $name - host name to check
               # $flags (optional, default: 0) - can be the bitwise OR of:
               #   &Net::SSLeay::X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT
               #   &Net::SSLeay::X509_CHECK_FLAG_NO_WILDCARDS
               #   &Net::SSLeay::X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS
               #   &Net::SSLeay::X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS
               #   &Net::SSLeay::X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS
               #   &Net::SSLeay::X509_CHECK_FLAG_NEVER_CHECK_SUBJECT
               # $peername (optional) - If not omitted and $host matches $cert,
               #                        a copy of the matching SAN or CN from
               #                        the peer certificate is stored in $peername.
               #
               # returns:
               #   1 for a successful match
               #   0 for a failed match
               #  -1 for an internal error
               #  -2 if the input is malformed

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_check_host.html>.

       •   X509_check_email

           COMPATIBILITY: not available in Net-SSLeay-1.68 and before; requires
           at least OpenSSL 1.0.2.

           Checks if the certificate matches the specified email address.

               my $rv = Net::SSLeay::X509_check_email($cert, $address, $flags);
               # $cert - value corresponding to openssl's X509 structure
               # $address - email address to check
               # $flags (optional, default: 0) - see X509_check_host()
               #
               # returns: see X509_check_host()

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_check_email.html>.

       •   X509_check_ip

           COMPATIBILITY: not available in Net-SSLeay-1.68 and before; requires
           at least OpenSSL 1.0.2.

           Checks if  the  certificate  matches  the  specified  IPv4  or  IPv6
           address.

               my $rv = Net::SSLeay::X509_check_ip($cert, $address, $flags);
               # $cert - value corresponding to openssl's X509 structure
               # $address - IP address to check in binary format, in network byte order
               # $flags (optional, default: 0) - see X509_check_host()
               #
               # returns: see X509_check_host()

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_check_ip.html>.

       •   X509_check_ip_asc

           COMPATIBILITY: not available in Net-SSLeay-1.68 and before; requires
           at least OpenSSL 1.0.2.

           Checks if  the  certificate  matches  the  specified  IPv4  or  IPv6
           address.

               my $rv = Net::SSLeay::X509_check_ip_asc($cert, $address, $flags);
               # $cert - value corresponding to openssl's X509 structure
               # $address - IP address to check in text representation
               # $flags (optional, default: 0) - see X509_check_host()
               #
               # returns: see X509_check_host()

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_check_ip_asc.html>.

       •   X509_certificate_type

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns bitmask with type of certificate $x.

               my $rv = Net::SSLeay::X509_certificate_type($x);
               # $x - value corresponding to openssl's X509 structure
               #
               # returns: (integer) bitmask with certificate type

               # to decode bitmask returned by this function use these constants:
               # &Net::SSLeay::EVP_PKS_DSA
               # &Net::SSLeay::EVP_PKS_EC
               # &Net::SSLeay::EVP_PKS_RSA
               # &Net::SSLeay::EVP_PKT_ENC
               # &Net::SSLeay::EVP_PKT_EXCH
               # &Net::SSLeay::EVP_PKT_EXP
               # &Net::SSLeay::EVP_PKT_SIGN
               # &Net::SSLeay::EVP_PK_DH
               # &Net::SSLeay::EVP_PK_DSA
               # &Net::SSLeay::EVP_PK_EC
               # &Net::SSLeay::EVP_PK_RSA

       •   X509_digest

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Computes digest/fingerprint of X509 $data using $type hash function.

               my $digest_value = Net::SSLeay::X509_digest($data, $type);
               # $data - value corresponding to openssl's X509 structure
               # $type - value corresponding to openssl's EVP_MD structure - e.g. got via EVP_get_digestbyname()
               #
               # returns: hash value (binary)

               # to get printable (hex) value of digest use:
               print unpack('H*', $digest_value);

       •   X509_issuer_and_serial_hash

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sort of a  checksum  of  issuer  name  and  serial  number  of  X509
           certificate  $x.   The result is not a full hash (e.g. sha-1), it is
           kind-of-a-hash truncated to the size of 'unsigned long'  (32  bits).
           The  resulting  value might differ across different openssl versions
           for the same X509 certificate.

               my $rv = Net::SSLeay::X509_issuer_and_serial_hash($x);
               # $x - value corresponding to openssl's X509 structure
               #
               # returns: number representing checksum

       •   X509_issuer_name_hash

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sort of a checksum of issuer  name  of  X509  certificate  $x.   The
           result  is  not  a  full  hash  (e.g.  sha-1),  it is kind-of-a-hash
           truncated to the size of 'unsigned long' (32 bits).   The  resulting
           value  might  differ  across different openssl versions for the same
           X509 certificate.

               my $rv = Net::SSLeay::X509_issuer_name_hash($x);
               # $x - value corresponding to openssl's X509 structure
               #
               # returns: number representing checksum

       •   X509_subject_name_hash

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sort of a checksum of subject name  of  X509  certificate  $x.   The
           result  is  not  a  full  hash  (e.g.  sha-1),  it is kind-of-a-hash
           truncated to the size of 'unsigned long' (32 bits).   The  resulting
           value  might  differ  across different openssl versions for the same
           X509 certificate.

               my $rv = Net::SSLeay::X509_subject_name_hash($x);
               # $x - value corresponding to openssl's X509 structure
               #
               # returns: number representing checksum

       •   X509_pubkey_digest

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Computes digest/fingerprint of  public  key  from  X509  certificate
           $data using $type hash function.

               my $digest_value = Net::SSLeay::X509_pubkey_digest($data, $type);
               # $data - value corresponding to openssl's X509 structure
               # $type - value corresponding to openssl's EVP_MD structure - e.g. got via EVP_get_digestbyname()
               #
               # returns: hash value (binary)

               # to get printable (hex) value of digest use:
               print unpack('H*', $digest_value);

       •   X509_set_issuer_name

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets issuer of X509 certificate $x to $name.

               my $rv = Net::SSLeay::X509_set_issuer_name($x, $name);
               # $x - value corresponding to openssl's X509 structure
               # $name - value corresponding to openssl's X509_NAME structure
               #
               # returns: 1 on success, 0 on failure

       •   X509_set_pubkey

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets public key of X509 certificate $x to $pkey.

               my $rv = Net::SSLeay::X509_set_pubkey($x, $pkey);
               # $x - value corresponding to openssl's X509 structure
               # $pkey - value corresponding to openssl's EVP_PKEY structure
               #
               # returns: 1 on success, 0 on failure

       •   X509_set_serialNumber

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets serial number of X509 certificate $x to $serial.

               my $rv = Net::SSLeay::X509_set_serialNumber($x, $serial);
               # $x - value corresponding to openssl's X509 structure
               # $serial - value corresponding to openssl's ASN1_INTEGER structure
               #
               # returns: 1 on success, 0 on failure

               # to create $serial value use one of these:
               $serial = Net::SSLeay::P_ASN1_INTEGER_set_hex('45ad6f');
               $serial = Net::SSLeay::P_ASN1_INTEGER_set_dec('7896541238529631478');
               $serial = Net::SSLeay::ASN1_INTEGER_set(45896);

       •   X509_set_subject_name

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets subject of X509 certificate $x to $name.

               my $rv = Net::SSLeay::X509_set_subject_name($x, $name);
               # $x - value corresponding to openssl's X509 structure
               # $name - value corresponding to openssl's X509_NAME structure
               #
               # returns: 1 on success, 0 on failure

       •   X509_set_version

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Set 'version' value for X509 certificate $ to $version.

               my $rv = Net::SSLeay::X509_set_version($x, $version);
               # $x - value corresponding to openssl's X509 structure
               # $version - (integer) version number
               #
               # returns: 1 on success, 0 on failure

       •   X509_sign

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sign  X509  certificate  $x  with  private  key  $pkey (using digest
           algorithm $md).

               my $rv = Net::SSLeay::X509_sign($x, $pkey, $md);
               # $x - value corresponding to openssl's X509 structure
               # $pkey - value corresponding to openssl's EVP_PKEY structure
               # $md - value corresponding to openssl's EVP_MD structure
               #
               # returns: 1 on success, 0 on failure

       •   X509_verify

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Verifies X509 object $a using public key $r (pubkey of issuing CA).

               my $rv = Net::SSLeay::X509_verify($x, $r);
               # $x - value corresponding to openssl's X509 structure
               # $r - value corresponding to openssl's EVP_PKEY structure
               #
               # returns: 0 - verify failure, 1 - verify OK, <0 - error

       •   X509_get_ext_count

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns the total number of extensions in X509 object $x.

               my $rv = Net::SSLeay::X509_get_ext_count($x);
               # $x - value corresponding to openssl's X509 structure
               #
               # returns: count of extensions

       •   X509_get_pubkey

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns public key corresponding to given X509 object $x.

               my $rv = Net::SSLeay::X509_get_pubkey($x);
               # $x - value corresponding to openssl's X509 structure
               #
               # returns: value corresponding to openssl's EVP_PKEY structure (0 on failure)

           NOTE: This method returns only the public key's  key  bits,  without
           the  algorithm  or parameters.  Use X509_get_X509_PUBKEY() to return
           the full public key (SPKI) instead.

       •   X509_get_X509_PUBKEY

           COMPATIBILITY: not available in Net-SSLeay-1.72 and before

           Returns the full public key (SPKI) of given X509 certificate $x.

               Net::SSLeay::X509_get_X509_PUBKEY($x);
               # $x - value corresponding to openssl's X509 structure
               #
               # returns: public key data in DER format (binary)

       •   X509_get_serialNumber

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns serial number of X509 certificate $x.

               my $rv = Net::SSLeay::X509_get_serialNumber($x);
               # $x - value corresponding to openssl's X509 structure
               #
               # returns: value corresponding to openssl's ASN1_INTEGER structure (0 on failure)

           See    "P_ASN1_INTEGER_get_dec",     "P_ASN1_INTEGER_get_hex"     or
           "ASN1_INTEGER_get" to decode ASN1_INTEGER object.

       •   X509_get0_serialNumber

           COMPATIBILITY: available in Net-SSLeay-1.86 onwards

           X509_get0_serialNumber()  is  the  same  as  X509_get_serialNumber()
           except it accepts a const parameter and returns a const result.

       •   X509_get_version

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns 'version' value of given X509 certificate $x.

               my $rv = Net::SSLeay::X509_get_version($x);
               # $x - value corresponding to openssl's X509 structure
               #
               # returns: (integer) version

       •   X509_get_ext

           Returns X509_EXTENSION from $x509 based on given position/index.

               my $rv = Net::SSLeay::X509_get_ext($x509, $index);
               # $x509 - value corresponding to openssl's X509 structure
               # $index - (integer) position/index of extension within $x509
               #
               # returns: value corresponding to openssl's X509_EXTENSION structure (0 on failure)

       •   X509_get_ext_by_NID

           Returns X509_EXTENSION from $x509 based on given NID.

               my $rv = Net::SSLeay::X509_get_ext_by_NID($x509, $nid, $loc);
               # $x509 - value corresponding to openssl's X509 structure
               # $nid - (integer) NID value
               # $loc - (integer) position to start lookup at
               #
               # returns: position/index of extension, negative value on error
               #          call Net::SSLeay::X509_get_ext($x509, $rv) to get the actual extension

       •   X509_get_fingerprint

           Returns fingerprint of certificate $cert.

           NOTE: Does not exactly correspond to any low level API function. The
           implementation is based on openssl's X509_digest().

               Net::SSLeay::X509_get_fingerprint($x509, $type);
               # $x509 - value corresponding to openssl's X509 structure
               # $type - (string) digest type, currently supported values:
               #         "md5"
               #         "sha1"
               #         "sha256"
               #         "ripemd160"
               #
               # returns: certificate digest - hexadecimal string (NOT binary data!)

       •   X509_get_issuer_name

           Return  an  X509_NAME  object  representing  the   issuer   of   the
           certificate $cert.

               my $rv = Net::SSLeay::X509_get_issuer_name($cert);
               # $cert - value corresponding to openssl's X509 structure
               #
               # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

       •   X509_get0_notAfter, X509_getm_notAfter and X509_get_notAfter

           COMPATIBILITY:  X509_get0_notAfter  and  X509_getm_notAfter  are not
           available in Net-SSLeay-1.92 and before

           Return an object giving the time after which the  certificate  $cert
           is not valid.

               my $rv  = Net::SSLeay::X509_get0_notAfter($cert);
               my $rvm = Net::SSLeay::X509_getm_notAfter($cert);
               # $cert - value corresponding to openssl's X509 structure
               #
               # returns: $rv  read-only value corresponding to openssl's ASN1_TIME structure
               #          $rvm mutable   value corresponding to openssl's ASN1_TIME structure

           To get human readable/printable form the return value you can use:

               my $time = Net::SSLeay::X509_get_notAfter($cert);
               print "notAfter=", Net::SSLeay::P_ASN1_TIME_get_isotime($time), "\n";

           NOTE:  X509_get_notAfter is an alias and deprecated in OpenSSL 1.1.0
           and later

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_get0_notAfter.html>

       •   X509_get0_notBefore, X509_getm_notBefore and X509_get_notBefore

           COMPATIBILITY:  X509_get0_notBefore  and X509_getm_notBefore are not
           available in Net-SSLeay-1.92 and before

           Return an object giving the time before which the certificate  $cert
           is not valid

               my $rv  = Net::SSLeay::X509_get0_notBefore($cert);
               my $rvm = Net::SSLeay::X509_getm_notBefore($cert);
               # $cert - value corresponding to openssl's X509 structure
               #
               # returns: $rv  read-only value corresponding to openssl's ASN1_TIME structure
               #          $rvm mutable   value corresponding to openssl's ASN1_TIME structure

           To get human readable/printable form the return value you can use:

               my $time = Net::SSLeay::X509_get_notBefore($cert);
               print "notBefore=", Net::SSLeay::P_ASN1_TIME_get_isotime($time), "\n";

           NOTE: X509_get_notBefore is an alias and deprecated in OpenSSL 1.1.0
           and later

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_get0_notBefore.html>

       •   X509_get_subjectAltNames

           NOTE: Does not exactly correspond to any low level API function.

           Returns the list of alternative subject names from X509  certificate
           $cert.

               my @rv = Net::SSLeay::X509_get_subjectAltNames($cert);
               # $cert - value corresponding to openssl's X509 structure
               #
               # returns: list containing pairs - name_type (integer), name_value (string)
               #          where name_type can be:
               #          0 - GEN_OTHERNAME
               #          1 - GEN_EMAIL
               #          2 - GEN_DNS
               #          3 - GEN_X400
               #          4 - GEN_DIRNAME
               #          5 - GEN_EDIPARTY
               #          6 - GEN_URI
               #          7 - GEN_IPADD
               #          8 - GEN_RID

           Note:  type 7 - GEN_IPADD contains the IP address as a packed binary
           address. GEN_RID is available in Net-SSLeay-1.90 and later.  Maximum
           length for returned RID string is currently 2500. Invalid and overly
           long   RID  values  are  skipped  and  not  returned.  GEN_X400  and
           GEN_EDIPARTY are not supported and will not be  returned  even  when
           present in the certificate.

       •   X509_get_subject_name

           Returns the subject of the certificate $cert.

               my $rv = Net::SSLeay::X509_get_subject_name($cert);
               # $cert - value corresponding to openssl's X509 structure
               #
               # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

       •   X509_gmtime_adj

           Adjust the ASN1_TIME object to the timestamp (in GMT).

               my $rv = Net::SSLeay::X509_gmtime_adj($s, $adj);
               # $s - value corresponding to openssl's ASN1_TIME structure
               # $adj - timestamp (seconds since 1.1.1970)
               #
               # returns: value corresponding to openssl's ASN1_TIME structure (0 on failure)

           BEWARE:  this  function  may  fail  for  dates  after  2038 as it is
           dependent on time_t size on your system (32bit time_t does not  work
           after 2038). Consider using "P_ASN1_TIME_set_isotime" instead).

       •   X509_load_cert_crl_file

           Takes  PEM  file  and loads all X509 certificates and X509 CRLs from
           that file into X509_LOOKUP structure.

               my $rv = Net::SSLeay::X509_load_cert_crl_file($ctx, $file, $type);
               # $ctx - value corresponding to openssl's X509_LOOKUP structure
               # $file - (string) file name
               # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
               #                          if not FILETYPE_PEM then behaves as Net::SSLeay::X509_load_cert_file()
               #
               # returns: 1 on success, 0 on failure

       •   X509_load_cert_file

           Loads/adds X509 certificate from $file to X509_LOOKUP structure

               my $rv = Net::SSLeay::X509_load_cert_file($ctx, $file, $type);
               # $ctx - value corresponding to openssl's X509_LOOKUP structure
               # $file - (string) file name
               # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
               #
               # returns: 1 on success, 0 on failure

       •   X509_load_crl_file

           Loads/adds X509 CRL from $file to X509_LOOKUP structure

               my $rv = Net::SSLeay::X509_load_crl_file($ctx, $file, $type);
               # $ctx - value corresponding to openssl's X509_LOOKUP structure
               # $file - (string) file name
               # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
               #
               # returns: 1 on success, 0 on failure

       •   X509_policy_level_get0_node

           COMPATIBILITY: no longer available in LibreSSL 3.8.0 and later

           ??? (more info needed)

               my $rv = Net::SSLeay::X509_policy_level_get0_node($level, $i);
               # $level - value corresponding to openssl's X509_POLICY_LEVEL structure
               # $i - (integer) index/position
               #
               # returns: value corresponding to openssl's X509_POLICY_NODE structure (0 on failure)

       •   X509_policy_level_node_count

           COMPATIBILITY: no longer available in LibreSSL 3.8.0 and later

           ??? (more info needed)

               my $rv = Net::SSLeay::X509_policy_level_node_count($level);
               # $level - value corresponding to openssl's X509_POLICY_LEVEL structure
               #
               # returns: (integer) node count

       •   X509_policy_node_get0_parent

           COMPATIBILITY: no longer available in LibreSSL 3.8.0 and later

           ??? (more info needed)

               my $rv = Net::SSLeay::X509_policy_node_get0_parent($node);
               # $node - value corresponding to openssl's X509_POLICY_NODE structure
               #
               # returns: value corresponding to openssl's X509_POLICY_NODE structure (0 on failure)

       •   X509_policy_node_get0_policy

           COMPATIBILITY: no longer available in LibreSSL 3.8.0 and later

           ??? (more info needed)

               my $rv = Net::SSLeay::X509_policy_node_get0_policy($node);
               # $node - value corresponding to openssl's X509_POLICY_NODE structure
               #
               # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

       •   X509_policy_node_get0_qualifiers

           COMPATIBILITY: no longer available in LibreSSL 3.8.0 and later

           ??? (more info needed)

               my $rv = Net::SSLeay::X509_policy_node_get0_qualifiers($node);
               # $node - value corresponding to openssl's X509_POLICY_NODE structure
               #
               # returns: value corresponding to openssl's STACK_OF(POLICYQUALINFO) structure (0 on failure)

       •   X509_policy_tree_free

           COMPATIBILITY: no longer available in LibreSSL 3.8.0 and later

           ??? (more info needed)

               Net::SSLeay::X509_policy_tree_free($tree);
               # $tree - value corresponding to openssl's X509_POLICY_TREE structure
               #
               # returns: no return value

       •   X509_policy_tree_get0_level

           COMPATIBILITY: no longer available in LibreSSL 3.8.0 and later

           ??? (more info needed)

               my $rv = Net::SSLeay::X509_policy_tree_get0_level($tree, $i);
               # $tree - value corresponding to openssl's X509_POLICY_TREE structure
               # $i - (integer) level index
               #
               # returns: value corresponding to openssl's X509_POLICY_LEVEL structure (0 on failure)

       •   X509_policy_tree_get0_policies

           COMPATIBILITY: no longer available in LibreSSL 3.8.0 and later

           ??? (more info needed)

               my $rv = Net::SSLeay::X509_policy_tree_get0_policies($tree);
               # $tree - value corresponding to openssl's X509_POLICY_TREE structure
               #
               # returns: value corresponding to openssl's STACK_OF(X509_POLICY_NODE) structure (0 on failure)

       •   X509_policy_tree_get0_user_policies

           COMPATIBILITY: no longer available in LibreSSL 3.8.0 and later

           ??? (more info needed)

               my $rv = Net::SSLeay::X509_policy_tree_get0_user_policies($tree);
               # $tree - value corresponding to openssl's X509_POLICY_TREE structure
               #
               # returns: value corresponding to openssl's STACK_OF(X509_POLICY_NODE) structure (0 on failure)

       •   X509_policy_tree_level_count

           COMPATIBILITY: no longer available in LibreSSL 3.8.0 and later

           ??? (more info needed)

               my $rv = Net::SSLeay::X509_policy_tree_level_count($tree);
               # $tree - value corresponding to openssl's X509_POLICY_TREE structure
               #
               # returns: (integer) count

       •   X509_verify_cert_error_string

           Returns a human readable error string for verification error $n.

               my $rv = Net::SSLeay::X509_verify_cert_error_string($n);
               # $n - (long) numeric error code
               #
               # returns: error string

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_STORE_CTX_get_error.html>

       •   P_X509_add_extensions

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Adds one or more X509 extensions to X509 object $x.

               my $rv = Net::SSLeay::P_X509_add_extensions($x, $ca_cert, $nid, $value);
               # $x - value corresponding to openssl's X509 structure
               # $ca_cert - value corresponding to openssl's X509 structure (issuer's cert - necessary for setting NID_authority_key_identifier)
               # $nid - NID identifying extension to be set
               # $value - extension value
               #
               # returns: 1 on success, 0 on failure

           You can set more extensions at once:

               my $rv = Net::SSLeay::P_X509_add_extensions($x509, $ca_cert,
                           &Net::SSLeay::NID_key_usage => 'digitalSignature,keyEncipherment',
                           &Net::SSLeay::NID_subject_key_identifier => 'hash',
                           &Net::SSLeay::NID_authority_key_identifier => 'keyid',
                           &Net::SSLeay::NID_authority_key_identifier => 'issuer',
                           &Net::SSLeay::NID_basic_constraints => 'CA:FALSE',
                           &Net::SSLeay::NID_ext_key_usage => 'serverAuth,clientAuth',
                           &Net::SSLeay::NID_netscape_cert_type => 'server',
                           &Net::SSLeay::NID_subject_alt_name => 'DNS:s1.dom.com,DNS:s2.dom.com,DNS:s3.dom.com',
                     );

       •   P_X509_copy_extensions

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Copies  X509  extensions from X509_REQ object to X509 object - handy
           when you need to turn X509_REQ into X509 certificate.

               Net::SSLeay::P_X509_copy_extensions($x509_req, $x509, $override);
               # $x509_req - value corresponding to openssl's X509_REQ structure
               # $x509 - value corresponding to openssl's X509 structure
               # $override - (integer) flag indication whether to override already existing items in $x509 (default 1)
               #
               # returns: 1 on success, 0 on failure

       •   P_X509_get_crl_distribution_points

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Get the list of CRL distribution points from X509 certificate.

               my @cdp = Net::SSLeay::P_X509_get_crl_distribution_points($x509);
               # $x509 - value corresponding to openssl's X509 structure
               #
               # returns: list of distribution points (usually URLs)

       •   P_X509_get_ext_key_usage

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Gets the list of extended key usage of given X509 certificate $cert.

               my @ext_usage = Net::SSLeay::P_X509_get_ext_key_usage($cert, $format);
               # $cert - value corresponding to openssl's X509 structure
               # $format - choose type of return values: 0=OIDs, 1=NIDs, 2=shortnames, 3=longnames
               #
               # returns: list of values

           Examples:

               my @extkeyusage_oid = Net::SSLeay::P_X509_get_ext_key_usage($x509,0);
               # returns for example: ("1.3.6.1.5.5.7.3.1", "1.3.6.1.5.5.7.3.2")

               my @extkeyusage_nid = Net::SSLeay::P_X509_get_ext_key_usage($x509,1);
               # returns for example: (129, 130)

               my @extkeyusage_sn  = Net::SSLeay::P_X509_get_ext_key_usage($x509,2);
               # returns for example: ("serverAuth", "clientAuth")

               my @extkeyusage_ln  = Net::SSLeay::P_X509_get_ext_key_usage($x509,3);
               # returns for example: ("TLS Web Server Authentication",  "TLS Web Client Authentication")

       •   P_X509_get_key_usage

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Gets the list of key usage of given X509 certificate $cert.

               my @keyusage = Net::SSLeay::P_X509_get_key_usage($cert);
               # $cert - value corresponding to openssl's X509 structure
               #
               # returns: list of key usage values which can be none, one or more from the following list:
               #          "digitalSignature"
               #          "nonRepudiation"
               #          "keyEncipherment"
               #          "dataEncipherment"
               #          "keyAgreement"
               #          "keyCertSign"
               #          "cRLSign"
               #          "encipherOnly"
               #          "decipherOnly"

       •   P_X509_get_netscape_cert_type

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Gets the list of Netscape  cert  types  of  given  X509  certificate
           $cert.

               Net::SSLeay::P_X509_get_netscape_cert_type($cert);
               # $cert - value corresponding to openssl's X509 structure
               #
               # returns: list of Netscape type values which can be none, one or more from the following list:
               #          "client"
               #          "server"
               #          "email"
               #          "objsign"
               #          "reserved"
               #          "sslCA"
               #          "emailCA"
               #          "objCA"

       •   P_X509_get_pubkey_alg

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns  ASN1_OBJECT  corresponding  to  X509 certificate public key
           algorithm.

               my $rv = Net::SSLeay::P_X509_get_pubkey_alg($x);
               # $x - value corresponding to openssl's X509 structure
               #
               # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

           To get textual representation use:

               my $alg = Net::SSLeay::OBJ_obj2txt(Net::SSLeay::P_X509_get_pubkey_alg($x509));
               # returns for example: "rsaEncryption"

       •   P_X509_get_signature_alg

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns ASN1_OBJECT corresponding to X509 signature key algorithm.

               my $rv = Net::SSLeay::P_X509_get_signature_alg($x);
               # $x - value corresponding to openssl's X509 structure
               #
               # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

           To get textual representation use:

               my $alg = Net::SSLeay::OBJ_obj2txt(Net::SSLeay::P_X509_get_signature_alg($x509));
               # returns for example: "sha1WithRSAEncryption"

       •   sk_X509_new_null

           Returns a new, empty, STACK_OF(X509) structure.

               my $rv = Net::SSLeay::sk_X509_new_null();
               #
               # returns: value corresponding to openssl's STACK_OF(X509) structure

       •   sk_X509_push

           Pushes an X509 structure onto a STACK_OF(X509) structure.

               my $rv = Net::SSLeay::sk_X509_push($sk_x509, $x509);
               # $sk_x509 - value corresponding to openssl's STACK_OF(X509) structure
               # $x509 - value corresponding to openssl's X509 structure
               #
               # returns: total number of elements after the operation, 0 on failure

       •   sk_X509_pop

           Pops an single X509 structure from a STACK_OF(X509) structure.

               my $x509 = Net::SSLeay::sk_X509_pop($sk_x509);
               # $sk_x509 - value corresponding to openssl's STACK_OF(X509) structure
               #
               # returns: a pointer to an X509 structure, undef on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/sk_TYPE_pop.html>

       •   sk_X509_shift

           Shifts an single X509 structure onto a STACK_OF(X509) structure.

               my $x509 = Net::SSLeay::sk_X509_shift($sk_x509, $x509);
               # $sk_x509 - value corresponding to openssl's STACK_OF(X509) structure
               # $x509 - value corresponding to openssl's X509 structure
               #
               # returns: a pointer to an X509 structure, undef on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/sk_TYPE_shift.html>

       •   sk_X509_unshift

           Unshifts an single X509 structure from a STACK_OF(X509) structure.

               my $rv = Net::SSLeay::sk_X509_unshift($sk_x509);
               # $sk_x509 - value corresponding to openssl's STACK_OF(X509) structure
               #
               # returns: total number of elements after the operation, 0 on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/sk_TYPE_unshift.html>

       •   sk_X509_insert

           Inserts  a  single  X509  structure  into  a  STACK_OF(X509)  at the
           specified index.

               my $rv = Net::SSLeay::sk_X509_insert($sk_x509, $x509, $index);
               # $sk_x509 - value corresponding to openssl's STACK_OF(X509) structure
               # $x509 - value corresponding to openssl's X509 structure
               # $index - integer - 0 based index
               #
               # returns: total number of elements after the operation, 0 on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/sk_TYPE_insert.html>

       •   sk_X509_delete

           Delete  a  single  X509  structure  from  a  STACK_OF(X509)  at  the
           specified index.

               my $x509 = Net::SSLeay::sk_X509_delete($sk_x509, $index);
               # $sk_x509 - value corresponding to openssl's STACK_OF(X509) structure
               # $index - integer - 0 based index
               #
               # returns: a pointer to an X509 structure, undef on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/sk_TYPE_delete.html>

       •   sk_X509_value

           Return  a  single  X509  structure  from  a  STACK_OF(X509)  at  the
           specified index.

               my $x509 = Net::SSLeay::sk_X509_value($sk_x509, $index);
               # $sk_x509 - value corresponding to openssl's STACK_OF(X509) structure
               # $index - integer - 0 based index
               #
               # returns: a pointer to an X509 structure, undef on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/sk_TYPE_value.html>

       •   sk_X509_num

           Return the number of X509 elements in a STACK_OF(X509).

               my $num = Net::SSLeay::sk_X509_num($sk_x509);
               # $sk_x509 - value corresponding to openssl's STACK_OF(X509) structure
               #
               # returns: the number of elements in the stack, -1 if the passed stack is NULL

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/sk_TYPE_num.html>

       Low level API: X509_REQ_* related functions

       •   X509_REQ_new

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Creates a new X509_REQ structure.

               my $rv = Net::SSLeay::X509_REQ_new();
               #
               # returns: value corresponding to openssl's X509_REQ structure (0 on failure)

       •   X509_REQ_free

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Free an allocated X509_REQ structure.

               Net::SSLeay::X509_REQ_free($x);
               # $x - value corresponding to openssl's X509_REQ structure
               #
               # returns: no return value

       •   X509_REQ_add1_attr_by_NID

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Adds an attribute whose name is defined by a  NID  $nid.  The  field
           value to be added is in $bytes.

               my $rv = Net::SSLeay::X509_REQ_add1_attr_by_NID($req, $nid, $type, $bytes);
               # $req - value corresponding to openssl's X509_REQ structure
               # $nid - (integer) NID value
               # $type - (integer) type of data in $bytes (see below)
               # $bytes - data to be set
               #
               # returns: 1 on success, 0 on failure

               # values for $type - use constants:
               # &Net::SSLeay::MBSTRING_UTF8     - $bytes contains utf8 encoded data
               # &Net::SSLeay::MBSTRING_ASC      - $bytes contains ASCII data

       •   X509_REQ_digest

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Computes  digest/fingerprint  of  X509_REQ  $data  using  $type hash
           function.

               my $digest_value = Net::SSLeay::X509_REQ_digest($data, $type);
               # $data - value corresponding to openssl's X509_REQ structure
               # $type - value corresponding to openssl's EVP_MD structure - e.g. got via EVP_get_digestbyname()
               #
               # returns: hash value (binary)

               # to get printable (hex) value of digest use:
               print unpack('H*', $digest_value);

       •   X509_REQ_get_attr_by_NID

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Retrieve the next  index  matching  $nid  after  $lastpos  ($lastpos
           should initially be set to -1).

               my $rv = Net::SSLeay::X509_REQ_get_attr_by_NID($req, $nid, $lastpos=-1);
               # $req - value corresponding to openssl's X509_REQ structure
               # $nid - (integer) NID value
               # $lastpos - [optional] (integer) index where to start search (default -1)
               #
               # returns: index (-1 if there are no more entries)

           Note:  use "P_X509_REQ_get_attr" to get the actual attribute value -
           e.g.

               my $index = Net::SSLeay::X509_REQ_get_attr_by_NID($req, $nid);
               my @attr_values = Net::SSLeay::P_X509_REQ_get_attr($req, $index);

       •   X509_REQ_get_attr_by_OBJ

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Retrieve the next  index  matching  $obj  after  $lastpos  ($lastpos
           should initially be set to -1).

               my $rv = Net::SSLeay::X509_REQ_get_attr_by_OBJ($req, $obj, $lastpos=-1);
               # $req - value corresponding to openssl's X509_REQ structure
               # $obj - value corresponding to openssl's ASN1_OBJECT structure
               # $lastpos - [optional] (integer) index where to start search (default -1)
               #
               # returns: index (-1 if there are no more entries)

           Note:  use "P_X509_REQ_get_attr" to get the actual attribute value -
           e.g.

               my $index = Net::SSLeay::X509_REQ_get_attr_by_NID($req, $nid);
               my @attr_values = Net::SSLeay::P_X509_REQ_get_attr($req, $index);

       •   X509_REQ_get_attr_count

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns the total number of attributes in $req.

               my $rv = Net::SSLeay::X509_REQ_get_attr_count($req);
               # $req - value corresponding to openssl's X509_REQ structure
               #
               # returns: (integer) items count

       •   X509_REQ_get_pubkey

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns public key corresponding to given X509_REQ object $x.

               my $rv = Net::SSLeay::X509_REQ_get_pubkey($x);
               # $x - value corresponding to openssl's X509_REQ structure
               #
               # returns: value corresponding to openssl's EVP_PKEY structure (0 on failure)

       •   X509_REQ_get_subject_name

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns X509_NAME object corresponding  to  subject  name  of  given
           X509_REQ object $x.

               my $rv = Net::SSLeay::X509_REQ_get_subject_name($x);
               # $x - value corresponding to openssl's X509_REQ structure
               #
               # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

       •   X509_REQ_get_version

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns 'version' value for given X509_REQ object $x.

               my $rv = Net::SSLeay::X509_REQ_get_version($x);
               # $x - value corresponding to openssl's X509_REQ structure
               #
               # returns: (integer) version e.g. 0 = "version 1"

       •   X509_REQ_set_pubkey

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets public key of given X509_REQ object $x to $pkey.

               my $rv = Net::SSLeay::X509_REQ_set_pubkey($x, $pkey);
               # $x - value corresponding to openssl's X509_REQ structure
               # $pkey - value corresponding to openssl's EVP_PKEY structure
               #
               # returns: 1 on success, 0 on failure

       •   X509_REQ_set_subject_name

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets  subject  name  of given X509_REQ object $x to X509_NAME object
           $name.

               my $rv = Net::SSLeay::X509_REQ_set_subject_name($x, $name);
               # $x - value corresponding to openssl's X509_REQ structure
               # $name - value corresponding to openssl's X509_NAME structure
               #
               # returns: 1 on success, 0 on failure

       •   X509_REQ_set_version

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets 'version' of given X509_REQ object $x to $version.

               my $rv = Net::SSLeay::X509_REQ_set_version($x, $version);
               # $x - value corresponding to openssl's X509_REQ structure
               # $version - (integer) e.g. 0 = "version 1"
               #
               # returns: 1 on success, 0 on failure

       •   X509_REQ_sign

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sign X509_REQ object $x with private key $pk (using digest algorithm
           $md).

               my $rv = Net::SSLeay::X509_REQ_sign($x, $pk, $md);
               # $x - value corresponding to openssl's X509_REQ structure
               # $pk - value corresponding to openssl's EVP_PKEY structure (requestor's private key)
               # $md - value corresponding to openssl's EVP_MD structure
               #
               # returns: 1 on success, 0 on failure

       •   X509_REQ_verify

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Verifies  X509_REQ  object  $x  using  public  key  $r  (pubkey   of
           requesting party).

               my $rv = Net::SSLeay::X509_REQ_verify($x, $r);
               # $x - value corresponding to openssl's X509_REQ structure
               # $r - value corresponding to openssl's EVP_PKEY structure
               #
               # returns: 0 - verify failure, 1 - verify OK, <0 - error

       •   P_X509_REQ_add_extensions

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Adds one or more X509 extensions to X509_REQ object $x.

               my $rv = Net::SSLeay::P_X509_REQ_add_extensions($x, $nid, $value);
               # $x - value corresponding to openssl's X509_REQ structure
               # $nid - NID identifying extension to be set
               # $value - extension value
               #
               # returns: 1 on success, 0 on failure

           You can set more extensions at once:

               my $rv = Net::SSLeay::P_X509_REQ_add_extensions($x509_req,
                       &Net::SSLeay::NID_key_usage => 'digitalSignature,keyEncipherment',
                       &Net::SSLeay::NID_basic_constraints => 'CA:FALSE',
                       &Net::SSLeay::NID_ext_key_usage => 'serverAuth,clientAuth',
                       &Net::SSLeay::NID_netscape_cert_type => 'server',
                       &Net::SSLeay::NID_subject_alt_name => 'DNS:s1.com,DNS:s2.com',
                       &Net::SSLeay::NID_crl_distribution_points => 'URI:http://pki.com/crl1,URI:http://pki.com/crl2',
                     );

       •   P_X509_REQ_get_attr

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns attribute value for X509_REQ's attribute at index $n.

               Net::SSLeay::P_X509_REQ_get_attr($req, $n);
               # $req - value corresponding to openssl's X509_REQ structure
               # $n - (integer) attribute index
               #
               # returns: value corresponding to openssl's ASN1_STRING structure

       Low level API: X509_CRL_* related functions

       •   X509_CRL_new

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Creates a new X509_CRL structure.

               my $rv = Net::SSLeay::X509_CRL_new();
               #
               # returns: value corresponding to openssl's X509_CRL structure (0 on failure)

       •   X509_CRL_free

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Free an allocated X509_CRL structure.

               Net::SSLeay::X509_CRL_free($x);
               # $x - value corresponding to openssl's X509_CRL structure
               #
               # returns: no return value

       •   X509_CRL_digest

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Computes  digest/fingerprint  of  X509_CRL  $data  using  $type hash
           function.

               my $digest_value = Net::SSLeay::X509_CRL_digest($data, $type);
               # $data - value corresponding to openssl's X509_CRL structure
               # $type - value corresponding to openssl's EVP_MD structure - e.g. got via EVP_get_digestbyname()
               #
               # returns: hash value (binary)

           Example:

               my $x509_crl;
               my $md = Net::SSLeay::EVP_get_digestbyname("sha1");
               my $digest_value = Net::SSLeay::X509_CRL_digest($x509_crl, $md);
               # to get printable (hex) value of digest use:
               print "digest=", unpack('H*', $digest_value), "\n";

       •   X509_CRL_get_ext

           COMPATIBILITY: not available in Net-SSLeay-1.54 and before

           Returns X509_EXTENSION from $x509 based on given position/index.

               my $rv = Net::SSLeay::X509_CRL_get_ext($x509, $index);
               # $x509 - value corresponding to openssl's X509_CRL structure
               # $index - (integer) position/index of extension within $x509
               #
               # returns: value corresponding to openssl's X509_EXTENSION structure (0 on failure)

       •   X509_CRL_get_ext_by_NID

           COMPATIBILITY: not available in Net-SSLeay-1.54 and before

           Returns X509_EXTENSION from $x509 based on given NID.

               my $rv = Net::SSLeay::X509_CRL_get_ext_by_NID($x509, $nid, $loc);
               # $x509 - value corresponding to openssl's X509_CRL structure
               # $nid - (integer) NID value
               # $loc - (integer) position to start lookup at
               #
               # returns: position/index of extension, negative value on error
               #          call Net::SSLeay::X509_CRL_get_ext($x509, $rv) to get the actual extension

       •   X509_CRL_get_ext_count

           COMPATIBILITY: not available in Net-SSLeay-1.54 and before

           Returns the total number of extensions in X509_CRL object $x.

               my $rv = Net::SSLeay::X509_CRL_get_ext_count($x);
               # $x - value corresponding to openssl's X509_CRL structure
               #
               # returns: count of extensions

       •   X509_CRL_get_issuer

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns X509_NAME object corresponding to the issuer of X509_CRL $x.

               my $rv = Net::SSLeay::X509_CRL_get_issuer($x);
               # $x - value corresponding to openssl's X509_CRL structure
               #
               # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

           See other "X509_NAME_*" functions to get more  info  from  X509_NAME
           structure.

       •   X509_CRL_get0_lastUpdate and X509_CRL_get_lastUpdate

           COMPATIBILITY:    X509_CRL_get0_lastUpdate    not    available    in
           Net-SSLeay-1.92 and before, X509_CRL_get_lastUpdate not available in
           Net-SSLeay-1.45 and before

           Returns 'lastUpdate' date-time value of X509_CRL object $x.

               my $rv = Net::SSLeay::X509_CRL_get0_lastUpdate($x);
               # $x - value corresponding to openssl's X509_CRL structure
               #
               # returns: read-only value corresponding to openssl's ASN1_TIME structure

           NOTE: X509_CRL_get_lastUpdate is an alias and deprecated in  OpenSSL
           1.1.0 and later

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_CRL_get0_lastUpdate.html>

       •   X509_CRL_get0_nextUpdate and X509_CRL_get_nextUpdate

           COMPATIBILITY:    X509_CRL_get0_nextUpdate    not    available    in
           Net-SSLeay-1.92 and before, X509_CRL_get_nextUpdate not available in
           Net-SSLeay-1.45 and before

           Returns 'nextUpdate' date-time value of X509_CRL object $x.

               my $rv = Net::SSLeay::X509_CRL_get0_nextUpdate($x);
               # $x - value corresponding to openssl's X509_CRL structure
               #
               # returns: read-only value corresponding to openssl's ASN1_TIME structure or 0 if 'nextUpdate' is not set

           NOTE:  X509_CRL_get_nextUpdate is an alias and deprecated in OpenSSL
           1.1.0 and later

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_CRL_get0_nextUpdate.html>

       •   X509_CRL_get_version

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns 'version' value of given X509_CRL structure $x.

               my $rv = Net::SSLeay::X509_CRL_get_version($x);
               # $x - value corresponding to openssl's X509_CRL structure
               #
               # returns: (integer) version

       •   X509_CRL_set_issuer_name

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets the issuer of X509_CRL object $x to X509_NAME object $name.

               my $rv = Net::SSLeay::X509_CRL_set_issuer_name($x, $name);
               # $x - value corresponding to openssl's X509_CRL structure
               # $name - value corresponding to openssl's X509_NAME structure
               #
               # returns: 1 on success, 0 on failure

       •   X509_CRL_set1_lastUpdate and X509_CRL_set_lastUpdate

           COMPATIBILITY:    X509_CRL_set1_lastUpdate    not    available    in
           Net-SSLeay-1.92 and before, X509_CRL_set_lastUpdate not available in
           Net-SSLeay-1.45 and before

           Sets 'lastUpdate' value of X509_CRL object $x to $tm.

               my $rv = Net::SSLeay::X509_CRL_set1_lastUpdate($x, $tm);
               # $x - value corresponding to openssl's X509_CRL structure
               # $tm - value corresponding to openssl's ASN1_TIME structure
               #
               # returns: 1 on success, 0 on failure

           NOTE: X509_CRL_set_lastUpdate is an alias and deprecated in  OpenSSL
           1.1.0 and later

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_CRL_set1_lastUpdate.html>

       •   X509_CRL_set1_nextUpdate and X509_CRL_set_nextUpdate

           COMPATIBILITY:    X509_CRL_set1_nextUpdate    not    available    in
           Net-SSLeay-1.92 and before, X509_CRL_set_nextUpdate not available in
           Net-SSLeay-1.45 and before

           Sets 'nextUpdate' value of X509_CRL object $x to $tm.

               my $rv = Net::SSLeay::X509_CRL_set1_nextUpdate($x, $tm);
               # $x - value corresponding to openssl's X509_CRL structure
               # $tm - value corresponding to openssl's ASN1_TIME structure
               #
               # returns: 1 on success, 0 on failure

           NOTE:  X509_CRL_set_nextUpdate is an alias and deprecated in OpenSSL
           1.1.0 and later

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_CRL_set1_nextUpdate.html>

       •   X509_CRL_set_version

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets 'version' value of given X509_CRL structure $x to $version.

               my $rv = Net::SSLeay::X509_CRL_set_version($x, $version);
               # $x - value corresponding to openssl's X509_CRL structure
               # $version - (integer) version number (1 = version 2 CRL)
               #
               # returns: 1 on success, 0 on failure

           Note  that if you want to use any X509_CRL extension you need to set
           "version 2 CRL" - "Net::SSLeay::X509_CRL_set_version($x, 1)".

       •   X509_CRL_sign

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sign X509_CRL  object  $x  with  private  key  $pkey  (using  digest
           algorithm $md).

               my $rv = Net::SSLeay::X509_CRL_sign($x, $pkey, $md);
               # $x - value corresponding to openssl's X509_CRL structure
               # $pkey - value corresponding to openssl's EVP_PKEY structure
               # $md - value corresponding to openssl's EVP_MD structure
               #
               # returns: 1 on success, 0 on failure

       •   X509_CRL_sort

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sorts  the  data  of X509_CRL object so it will be written in serial
           number order.

               my $rv = Net::SSLeay::X509_CRL_sort($x);
               # $x - value corresponding to openssl's X509_CRL structure
               #
               # returns: 1 on success, 0 on failure

       •   X509_CRL_verify

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Verifies X509_CRL object $a using public key $r (pubkey  of  issuing
           CA).

               my $rv = Net::SSLeay::X509_CRL_verify($a, $r);
               # $a - value corresponding to openssl's X509_CRL structure
               # $r - value corresponding to openssl's EVP_PKEY structure
               #
               # returns: 0 - verify failure, 1 - verify OK, <0 - error

       •   P_X509_CRL_add_revoked_serial_hex

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Adds given serial number $serial_hex to X509_CRL object $crl.

               Net::SSLeay::P_X509_CRL_add_revoked_serial_hex($crl, $serial_hex, $rev_time, $reason_code, $comp_time);
               # $crl - value corresponding to openssl's X509_CRL structure
               # $serial_hex - string (hexadecimal) representation of serial number
               # $rev_time - (revocation time) value corresponding to openssl's ASN1_TIME structure
               # $reason_code - [optional] (integer) reason code (see below) - default 0
               # $comp_time - [optional] (compromise time) value corresponding to openssl's ASN1_TIME structure
               #
               # returns: no return value

               # reason codes:
               # 0 - unspecified
               # 1 - keyCompromise
               # 2 - CACompromise
               # 3 - affiliationChanged
               # 4 - superseded
               # 5 - cessationOfOperation
               # 6 - certificateHold
               # 7 - (value 7 is not used)
               # 8 - removeFromCRL
               # 9 - privilegeWithdrawn
               # 10 - aACompromise

       •   P_X509_CRL_get_serial

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns serial number of X509_CRL object.

               my $rv = Net::SSLeay::P_X509_CRL_get_serial($crl);
               # $crl - value corresponding to openssl's X509_CRL structure
               #
               # returns: value corresponding to openssl's ASN1_INTEGER structure (0 on failure)

       •   P_X509_CRL_set_serial

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Sets serial number of X509_CRL object to $crl_number.

               my $rv = Net::SSLeay::P_X509_CRL_set_serial($crl, $crl_number);
               # $crl - value corresponding to openssl's X509_CRL structure
               # $crl_number - value corresponding to openssl's ASN1_INTEGER structure
               #
               # returns: 1 on success, 0 on failure

       •   P_X509_CRL_add_extensions

           COMPATIBILITY: not available in Net-SSLeay-1.88 and before

           Adds one or more X509 extensions to X509 CRL object $x.

               my $rv = Net::SSLeay::P_X509_CRL_add_extensions($x, $ca_cert, $nid, $value);
               # $x - value corresponding to openssl's X509 CRL structure
               # $ca_cert - value corresponding to openssl's X509 structure (issuer's cert - necessary for setting NID_authority_key_identifier)
               # $nid - NID identifying extension to be set
               # $value - extension value
               #
               # returns: 1 on success, 0 on failure

           For more details see "P_X509_add_extensions".

       Low level API: X509_EXTENSION_* related functions

       •   X509_EXTENSION_get_critical

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns 'critical' flag of given X509_EXTENSION object $ex.

               my $rv = Net::SSLeay::X509_EXTENSION_get_critical($ex);
               # $ex - value corresponding to openssl's X509_EXTENSION structure
               #
               # returns: (integer) 1 - critical, 0 - noncritical

       •   X509_EXTENSION_get_data

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns value (raw data) of X509_EXTENSION object $ne.

               my $rv = Net::SSLeay::X509_EXTENSION_get_data($ne);
               # $ne - value corresponding to openssl's X509_EXTENSION structure
               #
               # returns: value corresponding to openssl's ASN1_OCTET_STRING structure (0 on failure)

           Note:  you  can use "P_ASN1_STRING_get" to convert ASN1_OCTET_STRING
           into perl scalar variable.

       •   X509_EXTENSION_get_object

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns OID (ASN1_OBJECT) of X509_EXTENSION object $ne.

               my $rv = Net::SSLeay::X509_EXTENSION_get_object($ex);
               # $ex - value corresponding to openssl's X509_EXTENSION structure
               #
               # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

       •   X509V3_EXT_print

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns string representation of given X509_EXTENSION object $ext.

               Net::SSLeay::X509V3_EXT_print($ext, $flags, $utf8_decode);
               # $ext - value corresponding to openssl's X509_EXTENSION structure
               # $flags - [optional] (integer) Currently the flag argument is unused and should be set to 0
               # $utf8_decode - [optional] 0 or 1 whether the returned value should be utf8 decoded (default=0)
               #
               # returns: no return value

       •   X509V3_EXT_d2i

           Parses an extension and returns its internal structure.

               my $rv = Net::SSLeay::X509V3_EXT_d2i($ext);
               # $ext - value corresponding to openssl's X509_EXTENSION structure
               #
               # returns: pointer ???

       Low level API: X509_NAME_* related functions

       •   X509_NAME_ENTRY_get_data

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Retrieves the field value of $ne in and ASN1_STRING structure.

               my $rv = Net::SSLeay::X509_NAME_ENTRY_get_data($ne);
               # $ne - value corresponding to openssl's X509_NAME_ENTRY structure
               #
               # returns: value corresponding to openssl's ASN1_STRING structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_NAME_ENTRY_get_object.html>

       •   X509_NAME_ENTRY_get_object

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Retrieves the field name of $ne in and ASN1_OBJECT structure.

               my $rv = Net::SSLeay::X509_NAME_ENTRY_get_object($ne);
               # $ne - value corresponding to openssl's X509_NAME_ENTRY structure
               #
               # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_NAME_ENTRY_get_object.html>

       •   X509_NAME_new

           COMPATIBILITY: not available in Net-SSLeay-1.55 and before

           Creates a new X509_NAME structure.   Adds  a  field  whose  name  is
           defined  by  a  string  $field.  The  field  value to be added is in
           $bytes.

               my $rv = Net::SSLeay::X509_NAME_new();
               #
               # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

       •   X509_NAME_hash

           COMPATIBILITY: not available in Net-SSLeay-1.55 and before

           Sort of a checksum of issuer name $name.  The result is not  a  full
           hash  (e.g.  sha-1),  it  is kind-of-a-hash truncated to the size of
           'unsigned long' (32 bits).  The resulting value might differ  across
           different openssl versions for the same X509 certificate.

               my $rv = Net::SSLeay::X509_NAME_hash($name);
               # $name - value corresponding to openssl's X509_NAME structure
               #
               # returns: number representing checksum

       •   X509_NAME_add_entry_by_txt

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Adds  a  field  whose  name is defined by a string $field. The field
           value to be added is in $bytes.

               my $rv = Net::SSLeay::X509_NAME_add_entry_by_txt($name, $field, $type, $bytes, $len, $loc, $set);
               # $name - value corresponding to openssl's X509_NAME structure
               # $field - (string) field definition (name) - e.g. "organizationName"
               # $type - (integer) type of data in $bytes (see below)
               # $bytes - data to be set
               # $loc - [optional] (integer) index where the new entry is inserted: if it is -1 (default) it is appended
               # $set - [optional] (integer) determines how the new type is added. If it is 0 (default) a new RDN is created
               #
               # returns: 1 on success, 0 on failure

               # values for $type - use constants:
               # &Net::SSLeay::MBSTRING_UTF8     - $bytes contains utf8 encoded data
               # &Net::SSLeay::MBSTRING_ASC      - $bytes contains ASCII data

           Unicode note: when passing non-ascii (unicode) string in  $bytes  do
           not  forget to set "$flags = &Net::SSLeay::MBSTRING_UTF8" and encode
           the perl $string via "$bytes = encode('utf-8', $string)".

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_NAME_add_entry_by_txt.html>

       •   X509_NAME_add_entry_by_NID

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Adds a field whose name is defined by a NID $nid. The field value to
           be added is in $bytes.

               my $rv = Net::SSLeay::X509_NAME_add_entry_by_NID($name, $nid, $type, $bytes, $len, $loc, $set);
               # $name - value corresponding to openssl's X509_NAME structure
               # $nid - (integer) field definition - NID value
               # $type - (integer) type of data in $bytes (see below)
               # $bytes - data to be set
               # $loc - [optional] (integer) index where the new entry is inserted: if it is -1 (default) it is appended
               # $set - [optional] (integer) determines how the new type is added. If it is 0 (default) a new RDN is created
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_NAME_add_entry_by_txt.html>

       •   X509_NAME_add_entry_by_OBJ

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Adds a field whose name is defined by a  object  (OID)  $obj  .  The
           field value to be added is in $bytes.

               my $rv = Net::SSLeay::X509_NAME_add_entry_by_OBJ($name, $obj, $type, $bytes, $len, $loc, $set);
               # $name - value corresponding to openssl's X509_NAME structure
               # $obj - field definition - value corresponding to openssl's ASN1_OBJECT structure
               # $type - (integer) type of data in $bytes (see below)
               # $bytes - data to be set
               # $loc - [optional] (integer) index where the new entry is inserted: if it is -1 (default) it is appended
               # $set - [optional] (integer) determines how the new type is added. If it is 0 (default) a new RDN is created
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_NAME_add_entry_by_txt.html>

       •   X509_NAME_cmp

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Compares two X509_NAME objects.

               my $rv = Net::SSLeay::X509_NAME_cmp($a, $b);
               # $a - value corresponding to openssl's X509_NAME structure
               # $b - value corresponding to openssl's X509_NAME structure
               #
               # returns: 0 if $a matches $b; non zero otherwise

       •   X509_NAME_digest

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Computes digest/fingerprint of  X509_NAME  $data  using  $type  hash
           function.

               my $digest_value = Net::SSLeay::X509_NAME_digest($data, $type);
               # $data - value corresponding to openssl's X509_NAME structure
               # $type - value corresponding to openssl's EVP_MD structure - e.g. got via EVP_get_digestbyname()
               #
               # returns: hash value (binary)

               # to get printable (hex) value of digest use:
               print unpack('H*', $digest_value);

       •   X509_NAME_entry_count

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns the total number of entries in $name.

               my $rv = Net::SSLeay::X509_NAME_entry_count($name);
               # $name - value corresponding to openssl's X509_NAME structure
               #
               # returns: (integer) entries count

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_NAME_get_index_by_NID.html>

       •   X509_NAME_get_entry

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Retrieves the X509_NAME_ENTRY  from  $name  corresponding  to  index
           $loc.    Acceptable    values    for    $loc    run    from   0   to
           "Net::SSLeay::X509_NAME_entry_count($name) - 1". The value  returned
           is an internal pointer which must not be freed.

               my $rv = Net::SSLeay::X509_NAME_get_entry($name, $loc);
               # $name - value corresponding to openssl's X509_NAME structure
               # $loc - (integer) index of wanted entry
               #
               # returns: value corresponding to openssl's X509_NAME_ENTRY structure (0 on failure)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_NAME_get_index_by_NID.html>

       •   X509_NAME_print_ex

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns a string with human readable version of $name.

               Net::SSLeay::X509_NAME_print_ex($name, $flags, $utf8_decode);
               # $name - value corresponding to openssl's X509_NAME structure
               # $flags - [optional] conversion flags (default XN_FLAG_RFC2253) - see below
               # $utf8_decode - [optional] 0 or 1 whether the returned value should be utf8 decoded (default=0)
               #
               # returns: string representation of $name

               # available conversion flags - use constants:
               # &Net::SSLeay::XN_FLAG_COMPAT
               # &Net::SSLeay::XN_FLAG_DN_REV
               # &Net::SSLeay::XN_FLAG_DUMP_UNKNOWN_FIELDS
               # &Net::SSLeay::XN_FLAG_FN_ALIGN
               # &Net::SSLeay::XN_FLAG_FN_LN
               # &Net::SSLeay::XN_FLAG_FN_MASK
               # &Net::SSLeay::XN_FLAG_FN_NONE
               # &Net::SSLeay::XN_FLAG_FN_OID
               # &Net::SSLeay::XN_FLAG_FN_SN
               # &Net::SSLeay::XN_FLAG_MULTILINE
               # &Net::SSLeay::XN_FLAG_ONELINE
               # &Net::SSLeay::XN_FLAG_RFC2253
               # &Net::SSLeay::XN_FLAG_SEP_COMMA_PLUS
               # &Net::SSLeay::XN_FLAG_SEP_CPLUS_SPC
               # &Net::SSLeay::XN_FLAG_SEP_MASK
               # &Net::SSLeay::XN_FLAG_SEP_MULTILINE
               # &Net::SSLeay::XN_FLAG_SEP_SPLUS_SPC
               # &Net::SSLeay::XN_FLAG_SPC_EQ

           Most likely you will be fine with default:

               Net::SSLeay::X509_NAME_print_ex($name, &Net::SSLeay::XN_FLAG_RFC2253);

           Or you might want RFC2253-like output without utf8 chars escaping:

               use Net::SSLeay qw/XN_FLAG_RFC2253 ASN1_STRFLGS_ESC_MSB/;
               my $flag_rfc22536_utf8 = (XN_FLAG_RFC2253) & (~ ASN1_STRFLGS_ESC_MSB);
               my $result = Net::SSLeay::X509_NAME_print_ex($name, $flag_rfc22536_utf8, 1);

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_NAME_print_ex.html>

       •   X509_NAME_get_text_by_NID

           Retrieves  the text from the first entry in name which matches $nid,
           if no such entry exists -1 is returned.

           openssl  note:  this  is  a  legacy  function  which   has   various
           limitations  which  makes it of minimal use in practice. It can only
           find the first matching entry and will  copy  the  contents  of  the
           field  verbatim:  this  can  be  highly confusing if the target is a
           multicharacter string type like a BMPString or a UTF8String.

               Net::SSLeay::X509_NAME_get_text_by_NID($name, $nid);
               # $name - value corresponding to openssl's X509_NAME structure
               # $nid - NID value (integer)
               #
               # returns: text value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_NAME_get_index_by_NID.html>

       •   X509_NAME_oneline

           Return an ASCII version of $name.

               Net::SSLeay::X509_NAME_oneline($name);
               # $name - value corresponding to openssl's X509_NAME structure
               #
               # returns: (string) ASCII version of $name

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_NAME_print_ex.html>

       •   sk_X509_NAME_free

           Free an allocated STACK_OF(X509_NAME) structure.

               Net::SSLeay::sk_X509_NAME_free($sk);
               # $sk - value corresponding to openssl's STACK_OF(X509_NAME) structure
               #
               # returns: no return value

       •   sk_X509_NAME_num

           Return number of items in STACK_OF(X509_NAME)

               my $rv = Net::SSLeay::sk_X509_NAME_num($sk);
               # $sk - value corresponding to openssl's STACK_OF(X509_NAME) structure
               #
               # returns: number of items

       •   sk_X509_NAME_value

           Returns X509_NAME from position $index in STACK_OF(X509_NAME)

               my $rv = Net::SSLeay::sk_X509_NAME_value($sk, $i);
               # $sk - value corresponding to openssl's STACK_OF(X509_NAME) structure
               # $i - (integer) index/position
               #
               # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

       •   add_file_cert_subjects_to_stack

           Add a file of certs to a stack. All certs  in  $file  that  are  not
           already in the $stackCAs will be added.

               my $rv = Net::SSLeay::add_file_cert_subjects_to_stack($stackCAs, $file);
               # $stackCAs - value corresponding to openssl's STACK_OF(X509_NAME) structure
               # $file - (string) filename
               #
               # returns: 1 on success, 0 on failure

       •   add_dir_cert_subjects_to_stack

           Add  a directory of certs to a stack. All certs in $dir that are not
           already in the $stackCAs will be added.

               my $rv = Net::SSLeay::add_dir_cert_subjects_to_stack($stackCAs, $dir);
               # $stackCAs - value corresponding to openssl's STACK_OF(X509_NAME) structure
               # $dir - (string) the directory to append from. All files in this directory will be examined as potential certs. Any that are acceptable to SSL_add_dir_cert_subjects_to_stack() that are not already in the stack will be included.
               #
               # returns: 1 on success, 0 on failure

       Low level API: X509_STORE_* related functions

       •   X509_STORE_CTX_new

           returns a newly initialised X509_STORE_CTX structure.

       •   X509_STORE_CTX_init

           X509_STORE_CTX_init() sets up an  X509_STORE_CTX  for  a  subsequent
           verification  operation.   It  must  be  called  before each call to
           X509_verify_cert().

               my $rv = Net::SSLeay::X509_STORE_CTX_init($x509_store_ctx, $x509_store, $x509, $chain);
               # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure (required)
               # $x509_store - value corresponding to openssl's X509_STORE structure (optional)
               # $x509 - value corresponding to openssl's X509 structure (optional)
               # $chain - value corresponding to openssl's STACK_OF(X509) structure (optional)
               #
               # returns: 1 on success, 0 on failure
               #
               # Note: returns nothing with Net::SSLeay 1.90 and earlier.

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_STORE_CTX_init.html>

       •   X509_STORE_CTX_free

           Frees an X509_STORE_CTX structure.

               Net::SSLeay::X509_STORE_CTX_free($x509_store_ctx);
               # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure

       •   X509_verify_cert

           The  X509_verify_cert() function attempts to discover and validate a
           certificate chain based on parameters in ctx. A complete description
           of the process is contained in the verify(1) manual page.

           If this function returns  0,  use  X509_STORE_CTX_get_error  to  get
           additional error information.

               my $rv = Net::SSLeay::X509_verify_cert($x509_store_ctx);
               # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
               #
               # returns: 1 if a complete chain can be built and validated, otherwise 0

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_verify_cert.html>

       •   X509_STORE_CTX_get_current_cert

           Returns the certificate in ctx which caused the error  or  0  if  no
           certificate is relevant.

               my $rv = Net::SSLeay::X509_STORE_CTX_get_current_cert($x509_store_ctx);
               # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
               #
               # returns: value corresponding to openssl's X509 structure (0 on failure)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_STORE_CTX_get_error.html>

       •   X509_STORE_CTX_get0_cert

           COMPATIBILITY: not available in Net-SSLeay-1.88 and before; requires
           at least OpenSSL 1.1.0pre6 or LibreSSL 2.7.0

           Returns an internal pointer to the certificate being verified by the
           ctx.

               my $x509 = Net::SSLeay::X509_STORE_CTX_get0_cert($x509_store_ctx);
               # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
               #
               # returns: value corresponding to openssl's X509 structure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_STORE_CTX_get0_cert.html>

       •   X509_STORE_CTX_get1_chain

           Returns  a  returns  a complete validate chain if a previous call to
           X509_verify_cert() is successful.

               my $rv = Net::SSLeay::X509_STORE_CTX_get1_chain($x509_store_ctx);
               # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
               #
               # returns: value corresponding to openssl's STACK_OF(X509) structure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_STORE_CTX_get1_chain.html>

       •   X509_STORE_CTX_get_error

           Returns the error code of $ctx.

               my $rv = Net::SSLeay::X509_STORE_CTX_get_error($x509_store_ctx);
               # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
               #
               # returns: (integer) error code

           For   more   info   about   error   code   values   check   function
           "get_verify_result".

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_STORE_CTX_get_error.html>

       •   X509_STORE_CTX_get_error_depth

           Returns  the  depth  of  the  error.  This is a non-negative integer
           representing where in the certificate chain the error  occurred.  If
           it  is  zero it occurred in the end entity certificate, one if it is
           the certificate which signed the end entity certificate and so on.

               my $rv = Net::SSLeay::X509_STORE_CTX_get_error_depth($x509_store_ctx);
               # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
               #
               # returns: (integer) depth

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_STORE_CTX_get_error.html>

       •   X509_STORE_CTX_get_ex_data

           Is used to retrieve the information for $idx from $x509_store_ctx.

               my $rv = Net::SSLeay::X509_STORE_CTX_get_ex_data($x509_store_ctx, $idx);
               # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
               # $idx - (integer) index for application specific data
               #
               # returns: pointer to ???

       •   X509_STORE_CTX_set_ex_data

           Is   used   to   store   application   data  at  arg  for  idx  into
           $x509_store_ctx.

               my $rv = Net::SSLeay::X509_STORE_CTX_set_ex_data($x509_store_ctx, $idx, $data);
               # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
               # $idx - (integer) ???
               # $data - (pointer) ???
               #
               # returns: 1 on success, 0 on failure

       •   X509_STORE_CTX_set_cert

           Sets the certificate to be verified in $x509_store_ctx to $x.

               Net::SSLeay::X509_STORE_CTX_set_cert($x509_store_ctx, $x);
               # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
               # $x - value corresponding to openssl's X509 structure
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_STORE_CTX_new.html>

       •   X509_STORE_new

           Returns a newly initialized X509_STORE structure.

               my $rv = Net::SSLeay::X509_STORE_new();
               #
               # returns: value corresponding to openssl's X509_STORE structure (0 on failure)

       •   X509_STORE_free

           Frees an X509_STORE structure

               Net::SSLeay::X509_STORE_free($x509_store);
               # $x509_store - value corresponding to openssl's X509_STORE structure

       •   X509_STORE_add_lookup

           Adds a lookup to an X509_STORE for a given lookup method.

               my $method = &Net::SSLeay::X509_LOOKUP_hash_dir;
               my $rv = Net::SSLeay::X509_STORE_add_lookup($x509_store, $method);
               # $method - value corresponding to openssl's X509_LOOKUP_METHOD structure
               # $x509_store - value corresponding to openssl's X509_STORE structure
               #
               # returns: value corresponding to openssl's X509_LOOKUP structure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_STORE_add_lookup.html>

       •   X509_STORE_CTX_set_error

           Sets the error code of $ctx to $s. For example it might be used in a
           verification callback to set an error based on additional checks.

               Net::SSLeay::X509_STORE_CTX_set_error($x509_store_ctx, $s);
               # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
               # $s - (integer) error id
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_STORE_CTX_get_error.html>

       •   X509_STORE_add_cert

           Adds X509 certificate $x into the X509_STORE $store.

               my $rv = Net::SSLeay::X509_STORE_add_cert($store, $x);
               # $store - value corresponding to openssl's X509_STORE structure
               # $x - value corresponding to openssl's X509 structure
               #
               # returns: 1 on success, 0 on failure

       •   X509_STORE_add_crl

           Adds X509 CRL $x into the X509_STORE $store.

               my $rv = Net::SSLeay::X509_STORE_add_crl($store, $x);
               # $store - value corresponding to openssl's X509_STORE structure
               # $x - value corresponding to openssl's X509_CRL structure
               #
               # returns: 1 on success, 0 on failure

       •   X509_STORE_set1_param

           ??? (more info needed)

               my $rv = Net::SSLeay::X509_STORE_set1_param($store, $pm);
               # $store - value corresponding to openssl's X509_STORE structure
               # $pm - value corresponding to openssl's X509_VERIFY_PARAM structure
               #
               # returns: 1 on success, 0 on failure

       •   X509_LOOKUP_hash_dir

           Returns  an  X509_LOOKUP  structure  that instructs an X509_STORE to
           load files from a directory containing certificates  with  filenames
           in the format hash.N or crls with filenames in the format hash.rN

               my $rv = Net::SSLeay::X509_LOOKUP_hash_dir();
               #
               # returns: value corresponding to openssl's X509_LOOKUP_METHOD structure, with the hashed directory method

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_load_crl_file.html>

       •   X509_LOOKUP_add_dir

           Add a directory to an X509_LOOKUP structure, usually  obtained  from
           X509_STORE_add_lookup.

               my $method = &Net::SSLeay::X509_LOOKUP_hash_dir;
               my $lookup = Net::SSLeay::X509_STORE_add_lookup($x509_store, $method);
               my $type = &Net::SSLeay::X509_FILETYPE_PEM;
               Net::SSLeay::X509_LOOKUP_add_dir($lookup, $dir, $type);
               # $lookup - value corresponding to openssl's X509_LOOKUP structure
               # $dir - string path to a directory
               # $type - constant corresponding to the type of file in the directory - can be X509_FILETYPE_PEM, X509_FILETYPE_DEFAULT, or X509_FILETYPE_ASN1

       •   X509_STORE_set_flags

               Net::SSLeay::X509_STORE_set_flags($ctx, $flags);
               # $ctx - value corresponding to openssl's X509_STORE structure
               # $flags - (unsigned long) flags to be set (bitmask)
               #
               # returns: no return value

               # to create $flags value use corresponding constants like
               $flags = Net::SSLeay::X509_V_FLAG_CRL_CHECK();

           For      more      details      about     $flags     bitmask     see
           "X509_VERIFY_PARAM_set_flags".

       •   X509_STORE_set_purpose

               Net::SSLeay::X509_STORE_set_purpose($ctx, $purpose);
               # $ctx - value corresponding to openssl's X509_STORE structure
               # $purpose - (integer) purpose identifier
               #
               # returns: no return value

           For more details about $purpose identifier check "CTX_set_purpose".

       •   X509_STORE_set_trust

               Net::SSLeay::X509_STORE_set_trust($ctx, $trust);
               # $ctx - value corresponding to openssl's X509_STORE structure
               # $trust - (integer) trust identifier
               #
               # returns: no return value

           For more details about $trust identifier check "CTX_set_trust".

       Low Level API: X509_INFO related functions

       •   sk_X509_INFO_num

           Returns the number of values in a STACK_OF(X509_INFO) structure.

               my $rv = Net::SSLeay::sk_X509_INFO_num($sk_x509_info);
               # $sk_x509_info - value corresponding to openssl's STACK_OF(X509_INFO) structure
               #
               # returns: number of values in $sk_X509_info

       •   sk_X509_INFO_value

           Returns the value of a  STACK_OF(X509_INFO)  structure  at  a  given
           index.

               my $rv = Net::SSLeay::sk_X509_INFO_value($sk_x509_info, $index);
               # $sk_x509_info - value corresponding to openssl's STACK_OF(X509_INFO) structure
               # $index - index into the stack
               #
               # returns: value corresponding to openssl's X509_INFO structure at the given index

       •   P_X509_INFO_get_x509

           Returns the X509 structure stored in an X509_INFO structure.

               my $rv = Net::SSLeay::P_X509_INFO_get_x509($x509_info);
               # $x509_info - value corresponding to openssl's X509_INFO structure
               #
               # returns: value corresponding to openssl's X509 structure

       Low level API: X509_VERIFY_PARAM_* related functions

       •   X509_VERIFY_PARAM_add0_policy

           Enables policy checking (it is disabled by default) and adds $policy
           to the acceptable policy set.

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_add0_policy($param, $policy);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               # $policy - value corresponding to openssl's ASN1_OBJECT structure
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_VERIFY_PARAM_set_flags.html>

       •   X509_VERIFY_PARAM_add0_table

           ??? (more info needed)

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_add0_table($param);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               #
               # returns: 1 on success, 0 on failure

       •   X509_VERIFY_PARAM_add1_host

           COMPATIBILITY: not available in Net-SSLeay-1.82 and before; requires
           at least OpenSSL 1.0.2-beta2 or LibreSSL 2.7.0

           Adds an additional reference identifier that can  match  the  peer's
           certificate.

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_add1_host($param, $name);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               # $name - (string) name to be set
               #
               # returns: 1 on success, 0 on failure

           See    also    OpenSSL   docs,   "X509_VERIFY_PARAM_set1_host"   and
           "X509_VERIFY_PARAM_set_hostflags" for  more  information,  including
           wildcard matching.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_VERIFY_PARAM_set_flags.html>

       •   X509_VERIFY_PARAM_clear_flags

           Clears the flags $flags in param.

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_clear_flags($param, $flags);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               # $flags - (unsigned long) flags to be set (bitmask)
               #
               # returns: 1 on success, 0 on failure

           For     more     details     about      $flags      bitmask      see
           "X509_VERIFY_PARAM_set_flags".

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_VERIFY_PARAM_set_flags.html>

       •   X509_VERIFY_PARAM_free

           Frees up the X509_VERIFY_PARAM structure.

               Net::SSLeay::X509_VERIFY_PARAM_free($param);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               #
               # returns: no return value

       •   X509_VERIFY_PARAM_get0_peername

           COMPATIBILITY: not available in Net-SSLeay-1.82 and before; requires
           at least OpenSSL 1.0.2-beta2 or LibreSSL 2.7.0

           Returns the  DNS  hostname  or  subject  CommonName  from  the  peer
           certificate that matched one of the reference identifiers.

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_get0_peername($param);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               #
               # returns: (string) name e.g. '*.example.com' or undef

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_VERIFY_PARAM_set_flags.html>

       •   X509_VERIFY_PARAM_get_depth

           Returns the current verification depth.

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_get_depth($param);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               #
               # returns: (integer) depth

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_VERIFY_PARAM_set_flags.html>

       •   X509_VERIFY_PARAM_get_flags

           Returns the current verification flags.

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_get_flags($param);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               #
               # returns: (unsigned long) flags to be set (bitmask)

           For    more    details    about    returned    flags   bitmask   see
           "X509_VERIFY_PARAM_set_flags".

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_VERIFY_PARAM_set_flags.html>

       •   X509_VERIFY_PARAM_set_flags

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_set_flags($param, $flags);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               # $flags - (unsigned long) flags to be set (bitmask)
               #
               # returns: 1 on success, 0 on failure

               # to create $flags value use corresponding constants like
               $flags = Net::SSLeay::X509_V_FLAG_CRL_CHECK();

           For more details about $flags bitmask, see the OpenSSL docs below.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_VERIFY_PARAM_set_flags.html>

       •   X509_VERIFY_PARAM_inherit

           ??? (more info needed)

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_inherit($to, $from);
               # $to - value corresponding to openssl's X509_VERIFY_PARAM structure
               # $from - value corresponding to openssl's X509_VERIFY_PARAM structure
               #
               # returns: 1 on success, 0 on failure

       •   X509_VERIFY_PARAM_lookup

           Finds X509_VERIFY_PARAM by name.

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_lookup($name);
               # $name - (string) name we want to find
               #
               # returns: value corresponding to openssl's X509_VERIFY_PARAM structure (0 on failure)

       •   X509_VERIFY_PARAM_new

           Creates a new X509_VERIFY_PARAM structure.

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_new();
               #
               # returns: value corresponding to openssl's X509_VERIFY_PARAM structure (0 on failure)

       •   X509_VERIFY_PARAM_set1

           Sets the name of X509_VERIFY_PARAM structure $to to the  same  value
           as the name of X509_VERIFY_PARAM structure $from.

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_set1($to, $from);
               # $to - value corresponding to openssl's X509_VERIFY_PARAM structure
               # $from - value corresponding to openssl's X509_VERIFY_PARAM structure
               #
               # returns: 1 on success, 0 on failure

       •   X509_VERIFY_PARAM_set1_email

           COMPATIBILITY: not available in Net-SSLeay-1.82 and before; requires
           at least OpenSSL 1.0.2-beta1 or LibreSSL 2.7.0

           Sets the expected RFC822 email address to email.

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_set1_email($param, $email);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               # $email - (string) email to be set
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_VERIFY_PARAM_set_flags.html>

       •   X509_VERIFY_PARAM_set1_host

           COMPATIBILITY: not available in Net-SSLeay-1.82 and before; requires
           at least OpenSSL 1.0.2-beta1 or LibreSSL 2.7.0

           Sets the expected DNS  hostname  to  name  clearing  any  previously
           specified host name or names.

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_set1_host($param, $name);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               # $name - (string) name to be set
               #
               # returns: 1 on success, 0 on failure

           See    also    OpenSSL   docs,   "X509_VERIFY_PARAM_add1_host"   and
           "X509_VERIFY_PARAM_set_hostflags" for  more  information,  including
           wildcard matching.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_VERIFY_PARAM_set_flags.html>

       •   X509_VERIFY_PARAM_set1_ip

           COMPATIBILITY: not available in Net-SSLeay-1.82 and before; requires
           at least OpenSSL 1.0.2-beta1 or LibreSSL 2.7.0

           Sets the expected IP address to ip.

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_set1_ip($param, $ip);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               # $ip - (binary) 4 octet IPv4 or 16 octet IPv6 address
               #
               # returns: 1 on success, 0 on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_VERIFY_PARAM_set_flags.html>

       •   X509_VERIFY_PARAM_set1_ip_asc

           COMPATIBILITY: not available in Net-SSLeay-1.82 and before; requires
           at least OpenSSL 1.0.2-beta1 or LibreSSL 2.7.0

           Sets the expected IP address to ipasc.

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_set1_asc($param, $ipasc);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               # $ip - (string) IPv4 or IPv6 address
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_VERIFY_PARAM_set_flags.html>

       •   X509_VERIFY_PARAM_set1_name

           Sets the name of X509_VERIFY_PARAM structure $param to $name.

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_set1_name($param, $name);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               # $name - (string) name to be set
               #
               # returns: 1 on success, 0 on failure

       •   X509_VERIFY_PARAM_set1_policies

           Enables policy checking (it is disabled by  default)  and  sets  the
           acceptable  policy  set  to  policies.   Any  existing policy set is
           cleared. The policies parameter can be 0 to clear an existing policy
           set.

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_set1_policies($param, $policies);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               # $policies - value corresponding to openssl's STACK_OF(ASN1_OBJECT) structure
               #
               # returns: 1 on success, 0 on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_VERIFY_PARAM_set_flags.html>

       •   X509_VERIFY_PARAM_set_depth

           Sets  the  maximum  verification depth to depth. That is the maximum
           number of untrusted CA certificates that can appear in a chain.

               Net::SSLeay::X509_VERIFY_PARAM_set_depth($param, $depth);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               # $depth - (integer) depth to be set
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_VERIFY_PARAM_set_flags.html>

       •   X509_VERIFY_PARAM_set_hostflags

           COMPATIBILITY: not available in Net-SSLeay-1.82 and before; requires
           at least OpenSSL 1.0.2-beta2 or LibreSSL 2.7.0

               Net::SSLeay::X509_VERIFY_PARAM_set_hostflags($param, $flags);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               # $flags - (unsigned int) flags to be set (bitmask)
               #
               # returns: no return value

           See    also   OpenSSL   docs,    "X509_VERIFY_PARAM_add1_host"   and
           "X509_VERIFY_PARAM_set1_host" for more information.  The  flags  for
           controlling  wildcard  checks  and  other  features  are  defined in
           OpenSSL docs.

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_VERIFY_PARAM_set_flags.html>

       •   X509_VERIFY_PARAM_set_purpose

           Sets the verification purpose in $param to $purpose. This determines
           the  acceptable  purpose  of  the certificate chain, for example SSL
           client or SSL server.

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_set_purpose($param, $purpose);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               # $purpose - (integer) purpose identifier
               #
               # returns: 1 on success, 0 on failure

           For more details about $purpose identifier check "CTX_set_purpose".

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_VERIFY_PARAM_set_flags.html>

       •   X509_VERIFY_PARAM_set_time

           Sets  the  verification  time  in $param to $t. Normally the current
           time is used.

               Net::SSLeay::X509_VERIFY_PARAM_set_time($param, $t);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               # $t - (time_t) time in seconds since 1.1.1970
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/X509_VERIFY_PARAM_set_flags.html>

       •   X509_VERIFY_PARAM_set_trust

           Sets the trust setting in $param to $trust.

               my $rv = Net::SSLeay::X509_VERIFY_PARAM_set_trust($param, $trust);
               # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
               # $trust - (integer) trust identifier
               #
               # returns: 1 on success, 0 on failure

           For more details about $trust identifier check "CTX_set_trust".

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/X509_VERIFY_PARAM_set_flags.html>

       •   X509_VERIFY_PARAM_table_cleanup

           ??? (more info needed)

               Net::SSLeay::X509_VERIFY_PARAM_table_cleanup();
               #
               # returns: no return value

       Low level API: Cipher (EVP_CIPHER_*) related functions

       •   EVP_get_cipherbyname

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before

           Returns an EVP_CIPHER structure when passed a cipher name.

               my $rv = Net::SSLeay::EVP_get_cipherbyname($name);
               # $name - (string) cipher name e.g. 'aes-128-cbc', 'camellia-256-ecb', 'des-ede', ...
               #
               # returns: value corresponding to openssl's EVP_CIPHER structure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/EVP_EncryptInit.html>

       Low level API: Digest (EVP_MD_*) related functions

       •   OpenSSL_add_all_digests

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

               Net::SSLeay::OpenSSL_add_all_digests();
               # no args, no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OpenSSL_add_all_algorithms.html>

       •   P_EVP_MD_list_all

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before; requires
           at least OpenSSL 1.0.0

           NOTE: Does not exactly correspond to any low level API function

               my $rv = Net::SSLeay::P_EVP_MD_list_all();
               #
               # returns: arrayref - list of available digest names

           The  returned  digest  names  correspond  to  values   expected   by
           "EVP_get_digestbyname".

           Note that some of the digests are available by default and some only
           after calling "OpenSSL_add_all_digests".

       •   EVP_get_digestbyname

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

               my $rv = Net::SSLeay::EVP_get_digestbyname($name);
               # $name - string with digest name
               #
               # returns: value corresponding to openssl's EVP_MD structure

               # The $name param can be:
               # md2
               # md4
               # md5
               # mdc2
               # ripemd160
               # sha
               # sha1
               # sha224
               # sha256
               # sha512
               # whirlpool

           Or    better    check    the    supported    digests    by   calling
           "P_EVP_MD_list_all".

       •   EVP_MD_type

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

               my $rv = Net::SSLeay::EVP_MD_type($md);
               # $md - value corresponding to openssl's EVP_MD structure
               #
               # returns: the NID (integer) of the OBJECT IDENTIFIER representing the given message digest

           "EVP_MD_type" is a non-deprecated alias macro  of  "EVP_MD_get_type"
           since OpenSSL 3.0.0.

       •   EVP_MD_size

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

               my $rv = Net::SSLeay::EVP_MD_size($md);
               # $md - value corresponding to openssl's EVP_MD structure
               #
               # returns: the size of the message digest in bytes (e.g. 20 for SHA1)

       •   EVP_MD_get0_description

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 3.0.0-beta1, not in LibreSSL

           Return description of a message digest.

               my $rv = Net::SSLeay::EVP_MD_get0_description($md);
               # $md - value corresponding to openssl's EVP_MD structure
               #
               # returns: String, a freeform and digest implementation dependent description of the digest for display and human consumption. (e.g. sha256)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/EVP_MD_get0_description.html>

       •   EVP_MD_get0_name

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 3.0.0-beta1, not in LibreSSL

           Return one name of a message digest.

               my $rv = Net::SSLeay::EVP_MD_get0_description($md);
               # $md - value corresponding to openssl's EVP_MD structure
               #
               # returns: String, the name of the given message digest. For fetched message digests with multiple names, only one of them is returned; it's recommended to use EVP_MD_names_do_all() instead. (e.g. SHA2-256 or SHA256 for the same digest)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/EVP_MD_get0_name.html>

       •   EVP_MD_get_type

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 3.0.0-beta1, not in LibreSSL

           Return NID value of a message digest.

               my $rv = Net::SSLeay::EVP_MD_get_type($md);
               # $md - value corresponding to openssl's EVP_MD structure
               #
               # returns: Integer, the NID of the OBJECT IDENTIFIER representing the given message digest when passed an EVP_MD structure.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/EVP_MD_get_type.html>

       •   EVP_MD_CTX_md

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

               Net::SSLeay::EVP_MD_CTX_md($ctx);
               # $ctx - value corresponding to openssl's EVP_MD_CTX structure
               #
               # returns: value corresponding to openssl's EVP_MD structure

       •   EVP_MD_CTX_create

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

           Allocates, initializes and returns a digest context.

               my $rv = Net::SSLeay::EVP_MD_CTX_create();
               #
               # returns: value corresponding to openssl's EVP_MD_CTX structure

           The complete idea behind EVP_MD_CTX looks like this example:

               Net::SSLeay::OpenSSL_add_all_digests();

               my $md = Net::SSLeay::EVP_get_digestbyname("sha1");
               my $ctx = Net::SSLeay::EVP_MD_CTX_create();
               Net::SSLeay::EVP_DigestInit($ctx, $md);

               while(my $chunk = get_piece_of_data()) {
                   Net::SSLeay::EVP_DigestUpdate($ctx,$chunk);
               }

               my $result = Net::SSLeay::EVP_DigestFinal($ctx);
               Net::SSLeay::EVP_MD_CTX_destroy($ctx);

               print "digest=", unpack('H*', $result), "\n"; # print hex value

       •   EVP_DigestInit_ex

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

           Sets up digest context $ctx to use a digest $type from ENGINE $impl,
           $ctx must be initialized before calling  this  function,  type  will
           typically  be supplied by a function such as "EVP_get_digestbyname".
           If $impl is 0 then the default implementation  of  digest  $type  is
           used.

               my $rv = Net::SSLeay::EVP_DigestInit_ex($ctx, $type, $impl);
               # $ctx  - value corresponding to openssl's EVP_MD_CTX structure
               # $type - value corresponding to openssl's EVP_MD structure
               # $impl - value corresponding to openssl's ENGINE structure
               #
               # returns: 1 for success and 0 for failure

       •   EVP_DigestInit

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

           Behaves  in  the  same  way as "EVP_DigestInit_ex" except the passed
           context $ctx does not have to be initialized, and it always uses the
           default digest implementation.

               my $rv = Net::SSLeay::EVP_DigestInit($ctx, $type);
               # $ctx - value corresponding to openssl's EVP_MD_CTX structure
               # $type - value corresponding to openssl's EVP_MD structure
               #
               # returns: 1 for success and 0 for failure

       •   EVP_MD_CTX_destroy

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

           Cleans up digest context $ctx and frees up the  space  allocated  to
           it,   it   should   be  called  only  on  a  context  created  using
           "EVP_MD_CTX_create".

               Net::SSLeay::EVP_MD_CTX_destroy($ctx);
               # $ctx - value corresponding to openssl's EVP_MD_CTX structure
               #
               # returns: no return value

       •   EVP_DigestUpdate

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

               my $rv = Net::SSLeay::EVP_DigestUpdate($ctx, $data);
               # $ctx  - value corresponding to openssl's EVP_MD_CTX structure
               # $data - data to be hashed
               #
               # returns: 1 for success and 0 for failure

       •   EVP_DigestFinal_ex

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

           Retrieves   the   digest   value   from    $ctx.    After    calling
           "EVP_DigestFinal_ex"  no  additional calls to "EVP_DigestUpdate" can
           be made, but "EVP_DigestInit_ex" can be called to initialize  a  new
           digest operation.

               my $digest_value = Net::SSLeay::EVP_DigestFinal_ex($ctx);
               # $ctx - value corresponding to openssl's EVP_MD_CTX structure
               #
               # returns: hash value (binary)

               # to get printable (hex) value of digest use:
               print unpack('H*', $digest_value);

       •   EVP_DigestFinal

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

           Similar  to  "EVP_DigestFinal_ex"  except  the digest context ctx is
           automatically cleaned up.

               my $rv = Net::SSLeay::EVP_DigestFinal($ctx);
               # $ctx - value corresponding to openssl's EVP_MD_CTX structure
               #
               # returns: hash value (binary)

               # to get printable (hex) value of digest use:
               print unpack('H*', $digest_value);

       •   MD2

           COMPATIBILITY: not supported by default in OpenSSL 1.0.0

           Computes MD2 from given $data (all data  needs  to  be  loaded  into
           memory)

               my $digest = Net::SSLeay::MD2($data);
               print "digest(hexadecimal)=", unpack('H*', $digest);

       •   MD4

           Computes  MD4  from  given  $data  (all data needs to be loaded into
           memory)

               my $digest = Net::SSLeay::MD4($data);
               print "digest(hexadecimal)=", unpack('H*', $digest);

       •   MD5

           Computes MD5 from given $data (all data  needs  to  be  loaded  into
           memory)

               my $digest = Net::SSLeay::MD5($data);
               print "digest(hexadecimal)=", unpack('H*', $digest);

       •   RIPEMD160

           Computes  RIPEMD160  from  given  $data (all data needs to be loaded
           into memory)

               my $digest = Net::SSLeay::RIPEMD160($data);
               print "digest(hexadecimal)=", unpack('H*', $digest);

       •   SHA1

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

           Computes SHA1 from given $data (all data needs  to  be  loaded  into
           memory)

               my $digest = Net::SSLeay::SHA1($data);
               print "digest(hexadecimal)=", unpack('H*', $digest);

       •   SHA256

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before; requires
           at least OpenSSL 0.9.8

           Computes  SHA256  from given $data (all data needs to be loaded into
           memory)

               my $digest = Net::SSLeay::SHA256($data);
               print "digest(hexadecimal)=", unpack('H*', $digest);

       •   SHA512

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before; requires
           at least OpenSSL 0.9.8

           Computes SHA512 from given $data (all data needs to be  loaded  into
           memory)

               my $digest = Net::SSLeay::SHA512($data);
               print "digest(hexadecimal)=", unpack('H*', $digest);

       •   EVP_Digest

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

           Computes  "any" digest from given $data (all data needs to be loaded
           into memory)

               my $md = Net::SSLeay::EVP_get_digestbyname("sha1"); # or any other algorithm
               my $digest = Net::SSLeay::EVP_Digest($data, $md);
               print "digest(hexadecimal)=", unpack('H*', $digest);

       •   EVP_sha1

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

               my $md = Net::SSLeay::EVP_sha1();
               #
               # returns: value corresponding to openssl's EVP_MD structure

       •   EVP_sha256

           COMPATIBILITY: requires at least OpenSSL 0.9.8

               my $md = Net::SSLeay::EVP_sha256();
               #
               # returns: value corresponding to openssl's EVP_MD structure

       •   EVP_sha512

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before; requires
           at least OpenSSL 0.9.8

               my $md = Net::SSLeay::EVP_sha512();
               #
               # returns: value corresponding to openssl's EVP_MD structure

       •   EVP_add_digest

               my $rv = Net::SSLeay::EVP_add_digest($digest);
               # $digest - value corresponding to openssl's EVP_MD structure
               #
               # returns: 1 on success, 0 otherwise

       Low level API: CIPHER_* related functions

       •   CIPHER_get_name

           COMPATIBILITY: not available in Net-SSLeay-1.42 and before

           Returns name of the cipher used.

               my $rv = Net::SSLeay::CIPHER_get_name($cipher);
               # $cipher - value corresponding to openssl's SSL_CIPHER structure
               #
               # returns: (string) cipher name e.g. 'DHE-RSA-AES256-SHA', '(NONE)' if $cipher is undefined.

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CIPHER_get_name.html>

           Example:

               my $ssl_cipher = Net::SSLeay::get_current_cipher($ssl);
               my $cipher_name = Net::SSLeay::CIPHER_get_name($ssl_cipher);

       •   CIPHER_description

           COMPATIBILITY: doesn't work correctly in Net-SSLeay-1.88 and before

           Returns a textual description of the cipher used.

               my $rv = Net::SSLeay::CIPHER_description($cipher);
               # $cipher - value corresponding to openssl's SSL_CIPHER structure
               #
               # returns: (string) cipher description e.g. 'DHE-RSA-AES256-SHA SSLv3 Kx=DH Au=RSA Enc=AES(256) Mac=SHA1'

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CIPHER_description.html>

       •   CIPHER_get_bits

           COMPATIBILITY: $alg_bits doesn't work correctly  in  Net-SSLeay-1.88
           and before

           Returns the number of secret bits used for cipher.

               my $rv = Net::SSLeay::CIPHER_get_bits($cipher, $alg_bits);
               # $cipher - value corresponding to openssl's SSL_CIPHER structure
               # $alg_bits - [optional] empty scalar for storing additional return value
               #
               # returns: (integer) number of secret bits, 0 on error
               #          (integer) in $alg_bits for bits processed by the chosen algorithm

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CIPHER_get_bits.html>

           Example:

               # bits and alg_bits are not equal for e.g., TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA,
               # RFC 8422 name TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA
               my $alg_bits;
               my $bits = Net::SSLeay::CIPHER_get_bits($cipher, $alg_bits);
               # my $bits = Net::SSLeay::CIPHER_get_bits($cipher);
               print "bits: $bits, alg_bits: $alg_bits\n";

       •   CIPHER_get_version

           COMPATIBILITY: not available in Net-SSLeay-1.88 and before

           Returns version of SSL/TLS protocol that first defined the cipher

               my $rv = Net::SSLeay::CIPHER_get_version($cipher);
               # $cipher - value corresponding to openssl's SSL_CIPHER structure
               #
               # returns: (string) cipher name e.g. 'TLSv1/SSLv3' with some libraries, 'TLSv1.0' or 'TLSv1.3', '(NONE)' if $cipher is undefined.

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CIPHER_get_version.html>

       •   CIPHER_get_handshake_digest

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.1.1-pre1, not in LibreSSL

           Returns version of SSL/TLS protocol that first defined the cipher

               my $rv = Net::SSLeay::CIPHER_get_handshake_digest($cipher);
               # $cipher - value corresponding to openssl's SSL_CIPHER structure
               #
               # returns: A value corresponding to OpenSSL's EVP_MD structure for the digest used during the SSL/TLS handshake when using $cipher.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/ssl/SSL_CIPHER_get_handshake_digest.html>

       •   CIPHER_find

           COMPATIBILITY: not available in Net-SSLeay-1.92 and before; requires
           at least OpenSSL 1.0.2 or LibreSSL 3.4.0

           Returns a SSL_CIPHER structure from the  current  SSL  using  a  two
           octet cipher ID.

               my $cipher = Net::SSLeay::CIPHER_find($ssl, $id);
               # $ssl - value corresponding to OpenSSL SSL structure
               # $id - two octet cipher ID.
               #
               # returns: A value corresponding to OpenSSL SSL_CIPHER structure or undef if cipher is not found or an error occurs.

           Example  that  prints 'OpenSSL name is: TLS_AES_128_GCM_SHA256' with
           TLSv1.3 when the ciphersuite is enabled:

               # TLS Cipher Suite 0x13, 0x01 is TLS_AES_128_GCM_SHA256
               my $id = pack('n', 0x1301);
               my $cipher =  Net::SSLeay::CIPHER_find($ssl, $id);
               printf("OpenSSL name is: " . Net::SSLeay::CIPHER_get_name($cipher));

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CIPHER_find.html>

       Low level API: BN_* related functions

       •   BN_dup

           Creates and returns a new BIGNUM from an existing BIGNUM.

               my $bn = Net::SSLeay::BN_dup($from);
               # $from - value corresponding to BIGNUM structure
               #
               # returns: a new BIGNUM containing the value $from

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/BN_dup.html>

       •   BN_clear

           Clears BIGNUM data when it is no longer needed.

               Net::SSLeay::BN_clear($bn);
               # $bn - value corresponding to BIGNUM structure
               #
               # returns: nothing. $bn is set to 0.

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/BN_clear.html>

       •   BN_clear_free

           Clears and frees a previously allocated BIGNUM.

               Net::SSLeay::BN_clear_free($bn);
               # $bn - value corresponding to BIGNUM structure
               #
               # returns: nothing. $bn is no longer usable.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/BN_clear_free.html>

       •   BN_free

           Frees previously a allocated BIGNUM.

               Net::SSLeay::BN_free($bn);
               # $bn - value corresponding to BIGNUM structure
               #
               # returns: nothing. $bn is no longer usable.

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/BN_free.html>

       Low level API: RSA_* related functions

       •   RSA_generate_key

           Generates  a  key  pair  and  returns  it  in  a newly allocated RSA
           structure.  The pseudo-random number generator must be seeded  prior
           to calling RSA_generate_key.

               my $rv = Net::SSLeay::RSA_generate_key($bits, $e, $perl_cb, $perl_cb_arg);
               # $bits - (integer) modulus size in bits e.g. 512, 1024, 2048
               # $e - (integer) public exponent, an odd number, typically 3, 17 or 65537
               # $perl_cb - [optional] reference to perl callback function
               # $perl_cb_arg - [optional] data that will be passed to callback function when invoked
               #
               # returns: value corresponding to openssl's RSA structure (0 on failure)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/RSA_generate_key.html>

       •   RSA_free

           Frees the RSA structure and its components. The key is erased before
           the memory is returned to the system.

               Net::SSLeay::RSA_free($r);
               # $r - value corresponding to openssl's RSA structure
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/RSA_new.html>

       •   RSA_get_key_parameters

           COMPATIBILITY: not available when OpenSSL is 1.1.0 or later and Net-
           SSLeay is 1.92 or earlier

           Returns a list of pointers to BIGNUMs representing the parameters of
           the key in this order: "(n, e, d, p, q, dmp1, dmq1, iqmp)"

           Caution: returned list consists of direct pointers to BIGNUMs. These
           must  not  be  freed  by  the  caller. These pointers can be used to
           duplicate  a  BIGNUM,  which   would   need   to   be   blessed   as
           Crypt::OpenSSL::Bignum  for  further use. See Crypt::OpenSSL::Bignum
           and OpenSSL manual for more about "bless_pointer" to why BN_dup() is
           used.

               my (@params) = RSA_get_key_parameters($r);

               my $dup = Net::SSLeay::BN_dup($params[1]);
               my $e = Crypt::OpenSSL::Bignum->bless_pointer($dup);
               print "exponent: ", $e->to_decimal(), "\n";

           This function has no equivalent in OpenSSL or LibreSSL but  combines
           functions        "RSA_get0_key",        "RSA_get0_factors"       and
           "RSA_get0_crt_params" for an easier interface.

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/RSA_get0_key.html>

       Low level API: BIO_* related functions

       •   BIO_eof

           Returns  1  if  the  BIO  has read EOF, the precise meaning of 'EOF'
           varies according to the BIO type.

               my $rv = Net::SSLeay::BIO_eof($s);
               # $s - value corresponding to openssl's BIO structure
               #
               # returns: 1 if EOF has been reached 0 otherwise

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/BIO_ctrl.html>

       •   BIO_f_ssl

           Returns  the SSL BIO method. This is a filter BIO which is a wrapper
           round the OpenSSL SSL routines adding a BIO 'flavour' to SSL I/O.

               my $rv = Net::SSLeay::BIO_f_ssl();
               #
               # returns: value corresponding to openssl's BIO_METHOD structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/BIO_f_ssl.html>

       •   BIO_free

           Frees up a single BIO.

               my $rv = Net::SSLeay::BIO_free($bio);
               # $bio; - value corresponding to openssl's BIO structure
               #
               # returns: 1 on success, 0 on failure

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/BIO_new.html>

       •   BIO_new

           Returns a new BIO using method $type

               my $rv = Net::SSLeay::BIO_new($type);
               # $type - value corresponding to openssl's BIO_METHOD structure
               #
               # returns: value corresponding to openssl's BIO structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/BIO_new.html>

       •   BIO_new_buffer_ssl_connect

           Creates  a  new  BIO chain consisting of a buffering BIO, an SSL BIO
           (using ctx) and a connect BIO.

               my $rv = Net::SSLeay::BIO_new_buffer_ssl_connect($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: value corresponding to openssl's BIO structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/BIO_f_ssl.html>

       •   BIO_new_file

           Creates  a  new  file BIO with mode $mode the meaning of mode is the
           same as the stdio function fopen(). The BIO_CLOSE flag is set on the
           returned BIO.

               my $rv = Net::SSLeay::BIO_new_file($filename, $mode);
               # $filename - (string) filename
               # $mode - (string) opening mode (as mode by stdio function fopen)
               #
               # returns: value corresponding to openssl's BIO structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/BIO_s_file.html>

       •   BIO_new_ssl

           Allocates  an  SSL  BIO  using  SSL_CTX ctx and using client mode if
           client is non zero.

               my $rv = Net::SSLeay::BIO_new_ssl($ctx, $client);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $client - (integer) 0 or 1 - indicates ssl client mode
               #
               # returns: value corresponding to openssl's BIO structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/BIO_f_ssl.html>

       •   BIO_new_ssl_connect

           Creates  a  new  BIO  chain  consisting  of  an  SSL BIO (using ctx)
           followed by a connect BIO.

               my $rv = Net::SSLeay::BIO_new_ssl_connect($ctx);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               #
               # returns: value corresponding to openssl's BIO structure (0 on failure)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/BIO_f_ssl.html>

       •   BIO_pending

           Return the number of pending characters in the BIOs read buffers.

               my $rv = Net::SSLeay::BIO_pending($s);
               # $s - value corresponding to openssl's BIO structure
               #
               # returns: the amount of pending data

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/BIO_ctrl.html>

       •   BIO_wpending

           Return the number of pending characters in the BIOs write buffers.

               my $rv = Net::SSLeay::BIO_wpending($s);
               # $s - value corresponding to openssl's BIO structure
               #
               # returns: the amount of pending data

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/BIO_ctrl.html>

       •   BIO_read

           Read the underlying descriptor.

               Net::SSLeay::BIO_read($s, $max);
               # $s - value corresponding to openssl's BIO structure
               # $max - [optional] max. bytes to read (if not specified, the value 32768 is used)
               #
               # returns: data

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/BIO_read.html>

       •   BIO_write

           Attempts to write data from $buffer to BIO $b.

               my $rv = Net::SSLeay::BIO_write($b, $buffer);
               # $b - value corresponding to openssl's BIO structure
               # $buffer - data
               #
               # returns: amount of data successfully written
               #          or that no data was successfully read or written if the result is 0 or -1
               #          or -2 when the operation is not implemented in the specific BIO type

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/BIO_read.html>

       •   BIO_s_mem

           Return the memory BIO method function.

               my $rv = Net::SSLeay::BIO_s_mem();
               #
               # returns: value corresponding to openssl's BIO_METHOD structure (0 on failure)

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/BIO_s_mem.html>

       •   BIO_ssl_copy_session_id

           Copies an SSL session id between BIO chains from  and  to.  It  does
           this   by   locating   the  SSL  BIOs  in  each  chain  and  calling
           SSL_copy_session_id() on the internal SSL pointer.

               my $rv = Net::SSLeay::BIO_ssl_copy_session_id($to, $from);
               # $to - value corresponding to openssl's BIO structure
               # $from - value corresponding to openssl's BIO structure
               #
               # returns: 1 on success, 0 on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/BIO_f_ssl.html>

       •   BIO_ssl_shutdown

           Closes  down  an  SSL  connection  on BIO chain bio. It does this by
           locating the SSL BIO in the chain and calling SSL_shutdown() on  its
           internal SSL pointer.

               Net::SSLeay::BIO_ssl_shutdown($ssl_bio);
               # $ssl_bio - value corresponding to openssl's BIO structure
               #
               # returns: no return value

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/BIO_f_ssl.html>

       Low level API: Server side Server Name Indication (SNI) support

       •   set_tlsext_host_name

           TBA

       •   get_servername

           TBA

       •   get_servername_type

           TBA

       •   CTX_set_tlsext_servername_callback

           COMPATIBILITY: requires at least OpenSSL 0.9.8f

           This function is used in a server to support Server side Server Name
           Indication (SNI).

               Net::SSLeay::CTX_set_tlsext_servername_callback($ctx, $code);
               # $ctx - SSL context
               # $code - reference to a subroutine that will be called when a new connection is being initiated
               #
               # returns: no return value

           On the  client  side:  use  set_tlsext_host_name($ssl,  $servername)
           before initiating the SSL connection.

           On  the  server  side:  Set  up  an  additional  SSL_CTX()  for each
           different certificate.

           Add   a   servername    callback    to    each    SSL_CTX()    using
           CTX_set_tlsext_servername_callback().

           The  callback  function  is required to retrieve the client-supplied
           servername with get_servername(ssl). Figure out the right SSL_CTX to
           go with that host name, then switch the SSL object to  that  SSL_CTX
           with set_SSL_CTX().

           Example:

               # set callback
               Net::SSLeay::CTX_set_tlsext_servername_callback($ctx,
                   sub {
                       my $ssl = shift;
                       my $h = Net::SSLeay::get_servername($ssl);
                       Net::SSLeay::set_SSL_CTX($ssl, $hostnames{$h}->{ctx}) if exists $hostnames{$h};
                   } );

           More complete example:

               # ... initialize Net::SSLeay

               my %hostnames = (
                   'sni1' => { cert=>'sni1.pem', key=>'sni1.key' },
                   'sni2' => { cert=>'sni2.pem', key=>'sni2.key' },
               );

               # create a new context for each certificate/key pair
               for my $name (keys %hostnames) {
                   $hostnames{$name}->{ctx} = Net::SSLeay::CTX_new or die;
                   Net::SSLeay::CTX_set_cipher_list($hostnames{$name}->{ctx}, 'ALL');
                   Net::SSLeay::set_cert_and_key($hostnames{$name}->{ctx},
                   $hostnames{$name}->{cert}, $hostnames{$name}->{key}) or die;
               }

               # create default context
               my $ctx = Net::SSLeay::CTX_new or die;
               Net::SSLeay::CTX_set_cipher_list($ctx, 'ALL');
               Net::SSLeay::set_cert_and_key($ctx, 'cert.pem','key.pem') or die;

               # set callback
               Net::SSLeay::CTX_set_tlsext_servername_callback($ctx, sub {
                   my $ssl = shift;
                   my $h = Net::SSLeay::get_servername($ssl);
                   Net::SSLeay::set_SSL_CTX($ssl, $hostnames{$h}->{ctx}) if exists $hostnames{$h};
               } );

               # ... later

               $s = Net::SSLeay::new($ctx);
               Net::SSLeay::set_fd($s, fileno($accepted_socket));
               Net::SSLeay::accept($s);

       Low level API: NPN (next protocol negotiation) related functions

       NPN  is  being  replaced  with  ALPN,  a  more  recent TLS extension for
       application protocol negotiation that's in process of being  adopted  by
       IETF. Please look below for APLN API description.

       Simple approach for using NPN support looks like this:

           ### client side
           use Net::SSLeay;
           use IO::Socket::INET;

           Net::SSLeay::initialize();
           my $sock = IO::Socket::INET->new(PeerAddr=>'encrypted.google.com:443') or die;
           my $ctx = Net::SSLeay::CTX_tlsv1_new() or die;
           Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL);
           Net::SSLeay::CTX_set_next_proto_select_cb($ctx, ['http1.1','spdy/2']);
           my $ssl = Net::SSLeay::new($ctx) or die;
           Net::SSLeay::set_fd($ssl, fileno($sock)) or die;
           Net::SSLeay::connect($ssl);

           warn "client:negotiated=",Net::SSLeay::P_next_proto_negotiated($ssl), "\n";
           warn "client:last_status=", Net::SSLeay::P_next_proto_last_status($ssl), "\n";

           ### server side
           use Net::SSLeay;
           use IO::Socket::INET;

           Net::SSLeay::initialize();
           my $ctx = Net::SSLeay::CTX_tlsv1_new() or die;
           Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL);
           Net::SSLeay::set_cert_and_key($ctx, "cert.pem", "key.pem");
           Net::SSLeay::CTX_set_next_protos_advertised_cb($ctx, ['spdy/2','http1.1']);
           my $sock = IO::Socket::INET->new(LocalAddr=>'localhost', LocalPort=>5443, Proto=>'tcp', Listen=>20) or die;

           while (1) {
               my $ssl = Net::SSLeay::new($ctx);
               warn("server:waiting for incoming connection...\n");
               my $fd = $sock->accept();
               Net::SSLeay::set_fd($ssl, $fd->fileno);
               Net::SSLeay::accept($ssl);
               warn "server:negotiated=",Net::SSLeay::P_next_proto_negotiated($ssl),"\n";
               my $got = Net::SSLeay::read($ssl);
               Net::SSLeay::ssl_write_all($ssl, "length=".length($got));
               Net::SSLeay::free($ssl);
               $fd->close();
           }
           # check with: openssl s_client -connect localhost:5443 -nextprotoneg http/1.1,spdy/2

       Please  note  that  the  selection  (negotiation) is performed by client
       side, the server side simply advertise the list of supported protocols.

       Advanced  approach  allows  you  to  implement  your   own   negotiation
       algorithm.

           # see below documentation for:
           Net::SSLeay::CTX_set_next_proto_select_cb($ctx, $perl_callback_function, $callback_data);
           Net::SSLeay::CTX_set_next_protos_advertised_cb($ctx, $perl_callback_function, $callback_data);

       Detection of NPN support (works even in older Net::SSLeay versions):

           use Net::SSLeay;

           if (exists &Net::SSLeay::P_next_proto_negotiated) {
               # do NPN stuff
           }

       •   CTX_set_next_proto_select_cb

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before; requires
           at least OpenSSL 1.0.1

           NOTE:  You  need  CTX_set_next_proto_select_cb on client side of SSL
           connection.

           Simple usage - in this case a  "common"  negotiation  algorithm  (as
           implemented by openssl's function SSL_select_next_proto) is used.

               $rv = Net::SSLeay::CTX_set_next_proto_select_cb($ctx, $arrayref);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $arrayref - list of accepted protocols - e.g. ['http1.0', 'http1.1']
               #
               # returns: 0 on success, 1 on failure

           Advanced usage (you probably do not need this):

               $rv = Net::SSLeay::CTX_set_next_proto_select_cb($ctx, $perl_callback_function, $callback_data);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $perl_callback_function - reference to perl function
               # $callback_data - [optional] data to passed to callback function when invoked
               #
               # returns: 0 on success, 1 on failure

               # where callback function looks like
               sub npn_advertised_cb_invoke {
                   my ($ssl, $arrayref_proto_list_advertised_by_server, $callback_data) = @_;
                   my $status;
                   # ...
                   $status = 1;   # status can be:
                                 # 0 - OPENSSL_NPN_UNSUPPORTED
                                 # 1 - OPENSSL_NPN_NEGOTIATED
                                 # 2 - OPENSSL_NPN_NO_OVERLAP
                   return $status, ['http1.1','spdy/2']; # the callback has to return 2 values
               }

           To undefine/clear this callback use:

               Net::SSLeay::CTX_set_next_proto_select_cb($ctx, undef);

       •   CTX_set_next_protos_advertised_cb

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before; requires
           at least OpenSSL 1.0.1

           NOTE:  You  need  CTX_set_next_proto_select_cb on server side of SSL
           connection.

           Simple usage:

               $rv = Net::SSLeay::CTX_set_next_protos_advertised_cb($ctx, $arrayref);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $arrayref - list of advertised protocols - e.g. ['http1.0', 'http1.1']
               #
               # returns: 0 on success, 1 on failure

           Advanced usage (you probably do not need this):

               $rv = Net::SSLeay::CTX_set_next_protos_advertised_cb($ctx, $perl_callback_function, $callback_data);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $perl_callback_function - reference to perl function
               # $callback_data - [optional] data to passed to callback function when invoked
               #
               # returns: 0 on success, 1 on failure

               # where callback function looks like
               sub npn_advertised_cb_invoke {
                   my ($ssl, $callback_data) = @_;
                   # ...
                   return ['http1.1','spdy/2']; # the callback has to return arrayref
               }

           To undefine/clear this callback use:

               Net::SSLeay::CTX_set_next_protos_advertised_cb($ctx, undef);

       •   P_next_proto_negotiated

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before; requires
           at least OpenSSL 1.0.1

           Returns the name of negotiated protocol  for  given  SSL  connection
           $ssl.

               $rv = Net::SSLeay::P_next_proto_negotiated($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: (string) negotiated protocol name (or undef if no negotiation was done or failed with fatal error)

       •   P_next_proto_last_status

           COMPATIBILITY: not available in Net-SSLeay-1.45 and before; requires
           at least OpenSSL 1.0.1

           Returns  the result of the last negotiation for given SSL connection
           $ssl.

               $rv = Net::SSLeay::P_next_proto_last_status($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: (integer) negotiation status
               #          0 - OPENSSL_NPN_UNSUPPORTED
               #          1 - OPENSSL_NPN_NEGOTIATED
               #          2 - OPENSSL_NPN_NO_OVERLAP

       Low level API: ALPN (application  layer  protocol  negotiation)  related
       functions

       Application  protocol  can  be  negotiated  via two different mechanisms
       employing  two  different  TLS  extensions:  NPN  (obsolete)  and   ALPN
       (recommended).

       The  API  is rather similar, with slight differences reflecting protocol
       specifics. In particular, with ALPN the protocol negotiation takes place
       on server, while with NPN the client implements the protocol negotiation
       logic.

       With ALPN, the most basic implementation looks like this:

           ### client side
           use Net::SSLeay;
           use IO::Socket::INET;

           Net::SSLeay::initialize();
           my $sock = IO::Socket::INET->new(PeerAddr=>'encrypted.google.com:443') or die;
           my $ctx = Net::SSLeay::CTX_tlsv1_new() or die;
           Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL);
           Net::SSLeay::CTX_set_alpn_protos($ctx, ['http/1.1', 'http/2.0', 'spdy/3']);
           my $ssl = Net::SSLeay::new($ctx) or die;
           Net::SSLeay::set_fd($ssl, fileno($sock)) or die;
           Net::SSLeay::connect($ssl);

           warn "client:selected=",Net::SSLeay::P_alpn_selected($ssl), "\n";

           ### server side
           use Net::SSLeay;
           use IO::Socket::INET;

           Net::SSLeay::initialize();
           my $ctx = Net::SSLeay::CTX_tlsv1_new() or die;
           Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL);
           Net::SSLeay::set_cert_and_key($ctx, "cert.pem", "key.pem");
           Net::SSLeay::CTX_set_alpn_select_cb($ctx, ['http/1.1', 'http/2.0', 'spdy/3']);
           my $sock = IO::Socket::INET->new(LocalAddr=>'localhost', LocalPort=>5443, Proto=>'tcp', Listen=>20) or die;

           while (1) {
               my $ssl = Net::SSLeay::new($ctx);
               warn("server:waiting for incoming connection...\n");
               my $fd = $sock->accept();
               Net::SSLeay::set_fd($ssl, $fd->fileno);
               Net::SSLeay::accept($ssl);
               warn "server:selected=",Net::SSLeay::P_alpn_selected($ssl),"\n";
               my $got = Net::SSLeay::read($ssl);
               Net::SSLeay::ssl_write_all($ssl, "length=".length($got));
               Net::SSLeay::free($ssl);
               $fd->close();
           }
           # check with: openssl s_client -connect localhost:5443 -alpn spdy/3,http/1.1

       Advanced  approach  allows  you  to  implement  your   own   negotiation
       algorithm.

           # see below documentation for:
           Net::SSLeay::CTX_set_alpn_select_cb($ctx, $perl_callback_function, $callback_data);

       Detection of ALPN support (works even in older Net::SSLeay versions):

           use Net::SSLeay;

           if (exists &Net::SSLeay::P_alpn_selected) {
               # do ALPN stuff
           }

       •   CTX_set_alpn_select_cb

           COMPATIBILITY: not available in Net-SSLeay-1.55 and before; requires
           at least OpenSSL 1.0.2

           NOTE:   You  need  CTX_set_alpn_select_cb  on  server  side  of  TLS
           connection.

           Simple usage - in this case a  "common"  negotiation  algorithm  (as
           implemented by openssl's function SSL_select_next_proto) is used.

               $rv = Net::SSLeay::CTX_set_alpn_select_cb($ctx, $arrayref);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $arrayref - list of accepted protocols - e.g. ['http/2.0', 'http/1.1', 'spdy/3']
               #
               # returns: 0 on success, 1 on failure

           Advanced usage (you probably do not need this):

               $rv = Net::SSLeay::CTX_set_alpn_select_cb($ctx, $perl_callback_function, $callback_data);
               # $ctx - value corresponding to openssl's SSL_CTX structure
               # $perl_callback_function - reference to perl function
               # $callback_data - [optional] data to passed to callback function when invoked
               #
               # returns: 0 on success, 1 on failure

               # where callback function looks like
               sub alpn_select_cb_invoke {
                   my ($ssl, $arrayref_proto_list_advertised_by_client, $callback_data) = @_;
                   # ...
                   if ($negotiated) {
                       return 'http/2.0';
                   } else {
                       return undef;
                   }
               }

           To undefine/clear this callback use:

               Net::SSLeay::CTX_set_alpn_select_cb($ctx, undef);

       •   set_alpn_protos

           COMPATIBILITY: not available in Net-SSLeay-1.55 and before; requires
           at least OpenSSL 1.0.2

           NOTE: You need set_alpn_protos on client side of TLS connection.

           This   adds   list  of  supported  application  layer  protocols  to
           ClientHello message sent by a client.  It advertises the enumeration
           of supported protocols:

               Net::SSLeay::set_alpn_protos($ssl, ['http/1.1', 'http/2.0', 'spdy/3']);
               # returns 0 on success

       •   CTX_set_alpn_protos

           COMPATIBILITY: not available in Net-SSLeay-1.55 and before; requires
           at least OpenSSL 1.0.2

           NOTE: You need CTX_set_alpn_protos on client side of TLS connection.

           This  adds  list  of  supported  application  layer   protocols   to
           ClientHello message sent by a client.  It advertises the enumeration
           of supported protocols:

               Net::SSLeay::CTX_set_alpn_protos($ctx, ['http/1.1', 'http/2.0', 'spdy/3']);
               # returns 0 on success

       •   P_alpn_selected

           COMPATIBILITY: not available in Net-SSLeay-1.55 and before; requires
           at least OpenSSL 1.0.2

           Returns  the  name  of  negotiated protocol for given TLS connection
           $ssl.

               $rv = Net::SSLeay::P_alpn_selected($ssl);
               # $ssl - value corresponding to openssl's SSL structure
               #
               # returns: (string) negotiated protocol name (or undef if no negotiation was done or failed with fatal error)

       Low level API: DANE Support

       OpenSSL  version  1.0.2  adds   preliminary   support   RFC6698   Domain
       Authentication  of  Named  Entities  (DANE)  Transport Layer Association
       within OpenSSL

       •   SSL_get_tlsa_record_byname

           COMPATIBILITY: DELETED from net-ssleay, since it is not supported by
           OpenSSL

           In  order  to  facilitate  DANE  there  is   additional   interface,
           SSL_get_tlsa_record_byname, accepting hostname, port and socket type
           that  returns  packed  TLSA  record. In order to make it even easier
           there    is    additional    SSL_ctrl    function     that     calls
           SSL_get_tlsa_record_byname   for  you.  Latter  is  recommended  for
           programmers that wish to maintain broader binary compatibility, e.g.
           make application work with both 1.0.2 and prior  version  (in  which
           case call to SSL_ctrl with new code returning error would have to be
           ignored when running with prior version).

               Net::SSLeay::get_tlsa_record_byname($name, $port, $type);

       Low level API: Other functions

       •   COMP_add_compression_method

           Adds the compression method cm with the identifier id to the list of
           available compression methods.  This list is globally maintained for
           all  SSL  operations  within this application.  It cannot be set for
           specific SSL_CTX or SSL objects.

               my $rv = Net::SSLeay::COMP_add_compression_method($id, $cm);
               # $id - (integer) compression method id
               #       0 to 63:    methods defined by the IETF
               #       64 to 192:  external party methods assigned by IANA
               #       193 to 255: reserved for private use
               #
               # $cm - value corresponding to openssl's COMP_METHOD structure
               #
               # returns: 0 on success, 1 on failure (check the error queue to find out the reason)

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_COMP_add_compression_method.html>

       •   DH_free

           Frees  the  DH  structure  and its components. The values are erased
           before the memory is returned to the system.

               Net::SSLeay::DH_free($dh);
               # $dh - value corresponding to openssl's DH structure
               #
               # returns: no return value

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/DH_new.html>

       •   FIPS_mode_set

           Enable or disable FIPS mode in a FIPS capable OpenSSL.

               Net::SSLeay::FIPS_mode_set($enable);
               # $enable - (integer) 1 to enable, 0 to disable

       Low level API: EC related functions

       •   CTX_set_tmp_ecdh

           TBA

       •   EC_KEY_free

           TBA

       •   EC_KEY_new_by_curve_name

           TBA

       •   EC_KEY_generate_key

           Generates  a  EC  key  and  returns  it  in a newly allocated EC_KEY
           structure.  The EC key then can be used to create a PKEY  which  can
           be used in calls like X509_set_pubkey.

               my $key = Net::SSLeay::EVP_PKEY_new();
               my $ec  = Net::SSLeay::EC_KEY_generate_key($curve);
               Net::SSLeay::EVP_PKEY_assign_EC_KEY($key,$ec);

               # $curve - curve name like 'secp521r1' or the matching Id (integer) of the curve
               #
               # returns: value corresponding to openssl's EC_KEY structure (0 on failure)

           This  function  has  no  equivalent in OpenSSL but combines multiple
           OpenSSL functions for an easier interface.

       •   CTX_set_ecdh_auto, set_ecdh_auto

           These functions enable or disable the automatic curve  selection  on
           the    server    side    by    calling    SSL_CTX_set_ecdh_auto   or
           SSL_set_ecdh_auto respectively.  If enabled the  highest  preference
           curve  is automatically used for ECDH temporary keys used during key
           exchange.  This function is no longer available for OpenSSL 1.1.0 or
           higher.

               Net::SSLeay::CTX_set_ecdh_auto($ctx,1);
               Net::SSLeay::set_ecdh_auto($ssl,1);

       •   CTX_set1_curves_list, set1_curves_list

           These functions set the supported curves (in order of preference) by
           calling     SSL_CTX_set1_curves_list     or     SSL_set1_curves_list
           respectively.   For  a  TLS  client  these curves are offered to the
           server in the supported curves extension while on  the  server  side
           these  are  used to determine the shared curve.  These functions are
           only available since OpenSSL 1.1.0.

               Net::SSLeay::CTX_set1_curves_list($ctx,"P-521:P-384:P-256");
               Net::SSLeay::set1_curves_list($ssl,"P-521:P-384:P-256");

       •   CTX_set1_groups_list, set1_groups_list

           These functions set the supported groups (in order of preference) by
           calling     SSL_CTX_set1_groups_list     or     SSL_set1_groups_list
           respectively.   This is practically the same as CTX_set1_curves_list
           and set1_curves_list except that all  DH  groups  can  be  given  as
           supported  by  TLS  1.3.   These  functions are only available since
           OpenSSL 1.1.1.

               Net::SSLeay::CTX_set1_groups_list($ctx,"P-521:P-384:P-256");
               Net::SSLeay::set1_groups_list($ssl,"P-521:P-384:P-256");

       Low level API: OSSL_LIB_CTX and OSSL_PROVIDER related functions

       •   OSSL_LIB_CTX_get0_global_default

           Returns a concrete  (non  NULL)  reference  to  the  global  default
           library context.

               my $libctx = Net::SSLeay::OSSL_LIB_CTX_get0_global_default();
               # returns: a value corresponding to OSSL_LIB_CTX structure or false on failure

           Typically  it's  simpler  to  use  undef with functions that take an
           OSSL_LIB_CTX argument when global default library context is needed.

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/OSSL_LIB_CTX_get0_global_default.html>

       •   OSSL_PROVIDER_load

           Loads and initializes a provider

               my $provider = Net::SSLeay::OSSL_PROVIDER_load($libctx, $name);
               # $libctx - value corresponding to OSSL_LIB_CTX structure or undef
               # $name - (string) provider name, e.g., 'legacy'
               #
               # returns: a value corresponding to OSSL_PROVIDER or false on failure

           Using  undef  loads  the  provider within the global default library
           context.

               my $provider = Net::SSLeay::OSSL_PROVIDER_load(undef, 'legacy');

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/OSSL_PROVIDER_load.html>

       •   OSSL_PROVIDER_try_load

           Loads  and initializes a provider similar to OSSL_PROVIDER_load with
           additional fallback control.

               my $provider = Net::SSLeay::OSSL_PROVIDER_try_load($libctx, $name, $retain_fallbacks);
               # $libctx - value corresponding to OSSL_LIB_CTX structure or undef
               # $name - (string) provider name, e.g., 'legacy'
               # $retain_fallbacks - (integer) 0 or 1
               #
               # returns: a value corresponding to OSSL_PROVIDER or false on failure

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/OSSL_PROVIDER_try_load.html>

       •   OSSL_PROVIDER_unload

           Unloads the given provider.

               my $rv = Net::SSLeay::OSSL_PROVIDER_unload($provider);
               # $provider - a value corresponding to OSSL_PROVIDER
               #
               # returns: (integer) 1 on success, 0 on error

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OSSL_PROVIDER_unload.html>

       •   OSSL_PROVIDER_available

           Checks if a named provider is available for use.

               my $rv = Net::SSLeay::OSSL_PROVIDER_available($libctx, $name);
               # $libctx - value corresponding to OSSL_LIB_CTX structure or undef
               # $name - (string) provider name, e.g., 'legacy'
               #
               # returns: (integer) 1 if the named provider is available, otherwise 0.

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/OSSL_PROVIDER_available.html>

       •   OSSL_PROVIDER_do_all

           Iterates  over  all  loaded providers. A callback is called for each
           provider.

               my $rv = Net::SSLeay::OSSL_PROVIDER_do_all($libctx, $cb, $cbdata);
               # $libctx - value corresponding to OSSL_LIB_CTX structure or undef
               # $cb - reference to a perl callback function
               # $cbdata - data that will be passed to callback function
               #
               # returns: (integer) 1 if all callbacks returned 1, 0 the first time a callback returns 0.

           Example:

               sub do_all_cb {
                   my ($provider, $cbdata) = @_;

                   my $name = Net::SSLeay::OSSL_PROVIDER_get0_name($provider);
                   print "Callback for provider: '$name', cbdata: '$cbdata'\n";
                   return 1;
               }
               my $data_for_cb = 'Hello';

               # Triggers default provider automatic loading.
               Net::SSLeay::OSSL_PROVIDER_available(undef, 'default') || die 'default provider not available';
               Net::SSLeay::OSSL_PROVIDER_load(undef, 'legacy') || die 'load legacy';
               Net::SSLeay::OSSL_PROVIDER_load(undef, 'null')   || die 'load null';
               Net::SSLeay::OSSL_PROVIDER_do_all(undef, \&do_all_cb, $data_for_cb) || die 'a callback failed';

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/OSSL_PROVIDER_do_all.html>

       •   OSSL_PROVIDER_get0_name

           Returns the name of the given provider.

               my $name = Net::SSLeay::OSSL_PROVIDER_get0_name($provider);
               # $provider - a value corresponding to OSSL_PROVIDER
               #
               # returns: (string) provider name, e.g., 'legacy'

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/OSSL_PROVIDER_get0_name.html>

       •   OSSL_PROVIDER_self_test

           Runs the provider's self tests.

               my $rv = Net::SSLeay::OSSL_PROVIDER_self_test($provider);
               # $libctx - value corresponding to OSSL_LIB_CTX structure or undef
               # $provider - a value corresponding to OSSL_PROVIDER
               #
               # returns: (integer) returns 1 if the self tests pass, 0 on error

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/OSSL_PROVIDER_self_test.html>

       Low level API: TLS PSK related functions

       COMPATIBILITY: not available in Net-SSLeay-1.92 and before.  The TLSv1.3
       specific functions require at least OpenSSL 1.1.1 and the others require
       at least OpenSSL 1.0.0. Not available in LibreSSL.

       •   CTX_use_psk_identity_hint

           Set  PSK  identity  hint  for  SSL_CTX on TLS server for TLSv1.2 and
           earlier versions.

               my $ret = Net::SSLeay::CTX_use_psk_identity_hint($ctx, $hint);
               # $ctx - value corresponding to OpenSSL SSL_CTX structure
               # $hint - string, a hint sent to the TLS clients
               #
               # returns: 1 on success, 0 on failure

           Example:

               my $ret = Net::SSLeay::CTX_use_psk_identity_hint($ctx, 'ctx server identity_hint');

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_use_psk_identity_hint.html>

       •   use_psk_identity_hint

           Set  PSK identity hint for SSL on TLS server for TLSv1.2 and earlier
           versions.

               my $ret = Net::SSLeay::use_psk_identity_hint($ssl, $hint);
               # $ssl - value corresponding to OpenSSL SSL structure
               # $hint - string, a hint sent to the TLS clients
               #
               # returns: 1 on success, 0 on failure

           Example:

               my $ret = Net::SSLeay::use_psk_identity_hint($ssl, 'ssl server identity_hint');

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_use_psk_identity_hint.html>

       •   CTX_set_psk_server_callback

           Set  a callback for an SSL_CTX on TLS server for using PSKs with all
           TLS versions.

           NOTE: With TLSv1.3 Net::SSLeay::CTX_set_psk_find_session_callback or
           Net::SSLeay::set_psk_find_session_callback is recommended.

               # First set up a callback function.
               sub tls12_psk_cb {
                   my ($ssl, $identity, $max_psk_len) = @_;

                   # Note: $identity is potentially hostile user supplied data

                   my $psk = pack('H*', 'deadbeef');
                   return $psk if length $psk <= $max_psk_len;

                   return undef;
               }

               my $cb = \&tls12_psk_cb;
               Net::SSLeay::CTX_set_psk_server_callback($ctx, $cb);
               # $ctx - value corresponding to OpenSSL SSL_CTX structure
               # $cb - reference to callback function
               #
               # returns: no return value

           The callback function must return a PSK in packed binary format,  or
           "undef"  to  trigger  "unknown_psk_identity" alert and TLS handshake
           failure. If TLS handshake failure  without  PSK  specific  alert  is
           required, return packed random data.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_psk_server_callback.html>

       •   set_psk_server_callback

           Set a callback for an SSL on TLS server for using PSKs with all  TLS
           versions.

           NOTE: With TLSv1.3 Net::SSLeay::CTX_set_psk_find_session_callback or
           Net::SSLeay::set_psk_find_session_callback is recommended.

               Net::SSLeay::set_psk_server_callback($ssl, $cb);
               # $ssl - value corresponding to OpenSSL SSL structure
               # $cb - reference to callback function
               #
               # returns: no return value

           See  Net::SSLeay::CTX_set_psk_server_callback()  documentation for a
           full example with a callback.

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_psk_server_callback.html>

       •   CTX_set_psk_find_session_callback

           Set a callback for an SSL_CTX on TLS server for using TLSv1.3 PSKs.

               # First set up a callback function.
               sub tls13_psk_cb {
                   my ($ssl, $identity) = @_;

                   # Note: $identity is potentially hostile user supplied data

                   my $sess = Net::SSLeay::SESSION_new();
                   my $cipher = Net::SSLeay::CIPHER_find($ssl, pack('n', 0x1301));
                   Net::SSLeay::SESSION_set1_master_key($sess, pack('H*', 'deadbeef'));
                   Net::SSLeay::SESSION_set_cipher($sess, $cipher);
                   Net::SSLeay::SESSION_set_protocol_version($sess, Net::SSLeay::version($ssl));

                   return (1, $sess);
               }

               my $cb = \&tls13_psk_cb;
               Net::SSLeay::CTX_set_psk_find_session_callback($ctx, $cb);
               # $ctx - value corresponding to OpenSSL SSL_CTX structure
               # $cb - reference to callback function
               #
               # returns: no return value

           The  callback  function must return a two value list. When the first
           value is 0, the connection setup fails. When the first value  is  1,
           the  second value must be a valid "SSL_SESSION" or "undef". When the
           second value is a valid "SSL_SESSION", the  TLS  handshake  proceeds
           with  PSK  authentication. When the the second value is "undef", PSK
           is  not  used  the   TLS   handshake   proceeds   with   certificate
           authentication.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_psk_find_session_callback.html>

       •   set_psk_find_session_callback

           Set a callback for an SSL on TLS server for using TLSv1.3 PSKs.

               Net::SSLeay::set_psk_find_session_callback($ssl, $cb);
               # $ssl - value corresponding to OpenSSL SSL structure
               # $cb - reference to callback function
               #
               # returns: no return value

           See  Net::SSLeay::CTX_set_psk_find_session_callback()  documentation
           for a full example with a callback.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_set_psk_find_session_callback.html>

       •   CTX_set_psk_use_session_callback

           Set a callback for an SSL_CTX on TLS client for using TLSv1.3 PSKs.

               # First set up a callback function.
               sub tls13_use_psk_cb {
                   my ($ssl, $md) = @_;

                   my $psk_identity = "test-tls-psk";
                   my $sess = Net::SSLeay::SESSION_new();
                   my $cipher = Net::SSLeay::CIPHER_find($ssl, pack('n', 0x1301));
                   Net::SSLeay::SESSION_set1_master_key($sess, pack('H*', 'deadbeef'));
                   Net::SSLeay::SESSION_set_cipher($sess, $cipher);
                   Net::SSLeay::SESSION_set_protocol_version($sess, Net::SSLeay::TLS1_3_VERSION());

                   # Typically not defined, see OpenSSL manual
                   if ($md) {
                       my $sess_md = Net::SSLeay::CIPHER_get_handshake_digest($cipher);
                       my $md_type; $md_type = Net::SSLeay::EVP_MD_type($md) if $md;
                       my $sess_md_type = Net::SSLeay::EVP_MD_type($sess_md);

                       if ($md_type != $sess_md_type) {
                           # Example only: guess and try SHA384
                           my $switched_cipher = Net::SSLeay::CIPHER_find($ssl, pack('n', 0x1302));
                           my $switched_md = Net::SSLeay::CIPHER_get_handshake_digest($switched_cipher);
                           my $switched_md_type = Net::SSLeay::EVP_MD_type($switched_md);
                           if ($md_type != $switched_md_type) {
                               # Guessed wrong, can't proceed with mismatched digest function
                               Net::SSLeay::SESSION_free($sess);
                               return (0, undef, undef);
                           }
                           Net::SSLeay::SESSION_set_cipher($sess, $switched_cipher);
                       }
                   }

                   return (1, $psk_identity, $sess);
               }

               my $cb = \&tls13_use_psk_cb;
               Net::SSLeay::CTX_set_psk_use_session_callback($ctx, $cb);
               # $ctx - value corresponding to OpenSSL SSL_CTX structure
               # $cb - reference to callback function
               #
               # returns: no return value

           The callback function must return a two value list. When  the  first
           value  is  0, the connection setup fails. When the first value is 1,
           the second value must be a valid "SSL_SESSION" or "undef". When  the
           second  value  is  a valid "SSL_SESSION", the TLS handshake proceeds
           with PSK authentication. When the the second value is  "undef",  PSK
           is   not   used   the   TLS   handshake  proceeds  with  certificate
           authentication.

           Check                          openssl                           doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_psk_find_session_callback.html>

       •   set_psk_use_session_callback

           Set a callback for an SSL on TLS client for using TLSv1.3 PSKs.

               # First set up a callback function.
               sub tls13_psk_cb {
                   my ($ssl, $identity) = @_;

                   # Note: $identity is potentially hostile user supplied data

                   my $sess = Net::SSLeay::SESSION_new();
                   my $cipher = Net::SSLeay::CIPHER_find($ssl, pack('n', 0x1301));
                   Net::SSLeay::SESSION_set1_master_key($sess, pack('H*', 'deadbeef'));
                   Net::SSLeay::SESSION_set_cipher($sess, $cipher);
                   Net::SSLeay::SESSION_set_protocol_version($sess, Net::SSLeay::version($ssl));

                   return (1, $sess);
               }

               my $cb = \&tls13_psk_cb;
               Net::SSLeay::CTX_set_psk_find_session_callback($ctx, $cb);
               # $ctx - value corresponding to OpenSSL SSL_CTX structure
               # $cb - reference to callback function
               #
               # returns: no return value

           The  callback  function must return a two value list. When the first
           value is 0, the connection setup fails. When the first value  is  1,
           the  second value must be a valid "SSL_SESSION" or "undef". When the
           second value is a valid "SSL_SESSION", the  TLS  handshake  proceeds
           with  PSK  authentication. When the the second value is "undef", PSK
           is  not  used  the   TLS   handshake   proceeds   with   certificate
           authentication.

           Check                           openssl                          doc
           <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_psk_find_session_callback.html>

   Constants
       There are many openssl constants available in Net::SSLeay. You  can  use
       them like this:

           use Net::SSLeay;
           print &Net::SSLeay::NID_commonName;
           # or
           print Net::SSLeay::NID_commonName();

       Or you can import them and use:

           use Net::SSLeay qw/NID_commonName/;
           print &NID_commonName;
           # or
           print NID_commonName();
           # or
           print NID_commonName;

       The   constants  names  are  derived  from  openssl  constants,  however
       constants starting  with  "SSL_"  prefix  have  name  with  "SSL_"  part
       stripped   -  e.g.  openssl's  constant  "SSL_OP_ALL"  is  available  as
       "Net::SSLeay::OP_ALL"

       The list of all available constant names:

       The list below is automatically generated - do not manually  modify  it.
       To  add or remove a constant, edit helper_script/constants.txt, then run
       helper_script/update-exported-constants.

           AD_ACCESS_DENIED                        OPENSSL_INIT_NO_LOAD_CRYPTO_STRINGS
           AD_BAD_CERTIFICATE                      OPENSSL_INIT_NO_LOAD_SSL_STRINGS
           AD_BAD_CERTIFICATE_HASH_VALUE           OPENSSL_MODULES_DIR
           AD_BAD_CERTIFICATE_STATUS_RESPONSE      OPENSSL_PLATFORM
           AD_BAD_RECORD_MAC                       OPENSSL_VERSION
           AD_CERTIFICATE_EXPIRED                  OPENSSL_VERSION_MAJOR
           AD_CERTIFICATE_REQUIRED                 OPENSSL_VERSION_MINOR
           AD_CERTIFICATE_REVOKED                  OPENSSL_VERSION_NUMBER
           AD_CERTIFICATE_UNKNOWN                  OPENSSL_VERSION_PATCH
           AD_CERTIFICATE_UNOBTAINABLE             OPENSSL_VERSION_STRING
           AD_CLOSE_NOTIFY                         OP_ALL
           AD_DECODE_ERROR                         OP_ALLOW_CLIENT_RENEGOTIATION
           AD_DECOMPRESSION_FAILURE                OP_ALLOW_NO_DHE_KEX
           AD_DECRYPTION_FAILED                    OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
           AD_DECRYPT_ERROR                        OP_CIPHER_SERVER_PREFERENCE
           AD_EXPORT_RESTRICTION                   OP_CISCO_ANYCONNECT
           AD_HANDSHAKE_FAILURE                    OP_CLEANSE_PLAINTEXT
           AD_ILLEGAL_PARAMETER                    OP_COOKIE_EXCHANGE
           AD_INAPPROPRIATE_FALLBACK               OP_CRYPTOPRO_TLSEXT_BUG
           AD_INSUFFICIENT_SECURITY                OP_DISABLE_TLSEXT_CA_NAMES
           AD_INTERNAL_ERROR                       OP_DONT_INSERT_EMPTY_FRAGMENTS
           AD_MISSING_EXTENSION                    OP_ENABLE_KTLS
           AD_NO_APPLICATION_PROTOCOL              OP_ENABLE_MIDDLEBOX_COMPAT
           AD_NO_CERTIFICATE                       OP_EPHEMERAL_RSA
           AD_NO_RENEGOTIATION                     OP_IGNORE_UNEXPECTED_EOF
           AD_PROTOCOL_VERSION                     OP_LEGACY_SERVER_CONNECT
           AD_RECORD_OVERFLOW                      OP_MICROSOFT_BIG_SSLV3_BUFFER
           AD_UNEXPECTED_MESSAGE                   OP_MICROSOFT_SESS_ID_BUG
           AD_UNKNOWN_CA                           OP_MSIE_SSLV2_RSA_PADDING
           AD_UNKNOWN_PSK_IDENTITY                 OP_NETSCAPE_CA_DN_BUG
           AD_UNRECOGNIZED_NAME                    OP_NETSCAPE_CHALLENGE_BUG
           AD_UNSUPPORTED_CERTIFICATE              OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
           AD_UNSUPPORTED_EXTENSION                OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
           AD_USER_CANCELLED                       OP_NON_EXPORT_FIRST
           ASN1_STRFLGS_ESC_CTRL                   OP_NO_ANTI_REPLAY
           ASN1_STRFLGS_ESC_MSB                    OP_NO_CLIENT_RENEGOTIATION
           ASN1_STRFLGS_ESC_QUOTE                  OP_NO_COMPRESSION
           ASN1_STRFLGS_RFC2253                    OP_NO_ENCRYPT_THEN_MAC
           ASYNC_NO_JOBS                           OP_NO_EXTENDED_MASTER_SECRET
           ASYNC_PAUSED                            OP_NO_QUERY_MTU
           CB_ACCEPT_EXIT                          OP_NO_RENEGOTIATION
           CB_ACCEPT_LOOP                          OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
           CB_ALERT                                OP_NO_SSL_MASK
           CB_CONNECT_EXIT                         OP_NO_SSLv2
           CB_CONNECT_LOOP                         OP_NO_SSLv3
           CB_EXIT                                 OP_NO_TICKET
           CB_HANDSHAKE_DONE                       OP_NO_TLSv1
           CB_HANDSHAKE_START                      OP_NO_TLSv1_1
           CB_LOOP                                 OP_NO_TLSv1_2
           CB_READ                                 OP_NO_TLSv1_3
           CB_READ_ALERT                           OP_PKCS1_CHECK_1
           CB_WRITE                                OP_PKCS1_CHECK_2
           CB_WRITE_ALERT                          OP_PRIORITIZE_CHACHA
           CLIENT_HELLO_CB                         OP_SAFARI_ECDHE_ECDSA_BUG
           CLIENT_HELLO_ERROR                      OP_SINGLE_DH_USE
           CLIENT_HELLO_RETRY                      OP_SINGLE_ECDH_USE
           CLIENT_HELLO_SUCCESS                    OP_SSLEAY_080_CLIENT_DH_BUG
           CONF_MFLAGS_DEFAULT_SECTION             OP_SSLREF2_REUSE_CERT_TYPE_BUG
           CONF_MFLAGS_IGNORE_ERRORS               OP_TLSEXT_PADDING
           CONF_MFLAGS_IGNORE_MISSING_FILE         OP_TLS_BLOCK_PADDING_BUG
           CONF_MFLAGS_IGNORE_RETURN_CODES         OP_TLS_D5_BUG
           CONF_MFLAGS_NO_DSO                      OP_TLS_ROLLBACK_BUG
           CONF_MFLAGS_SILENT                      READING
           ERROR_NONE                              RECEIVED_SHUTDOWN
           ERROR_SSL                               RETRY_VERIFY
           ERROR_SYSCALL                           RSA_3
           ERROR_WANT_ACCEPT                       RSA_F4
           ERROR_WANT_ASYNC                        R_BAD_AUTHENTICATION_TYPE
           ERROR_WANT_ASYNC_JOB                    R_BAD_CHECKSUM
           ERROR_WANT_CLIENT_HELLO_CB              R_BAD_MAC_DECODE
           ERROR_WANT_CONNECT                      R_BAD_RESPONSE_ARGUMENT
           ERROR_WANT_READ                         R_BAD_SSL_FILETYPE
           ERROR_WANT_RETRY_VERIFY                 R_BAD_SSL_SESSION_ID_LENGTH
           ERROR_WANT_WRITE                        R_BAD_STATE
           ERROR_WANT_X509_LOOKUP                  R_BAD_WRITE_RETRY
           ERROR_ZERO_RETURN                       R_CHALLENGE_IS_DIFFERENT
           EVP_PKS_DSA                             R_CIPHER_TABLE_SRC_ERROR
           EVP_PKS_EC                              R_INVALID_CHALLENGE_LENGTH
           EVP_PKS_RSA                             R_NO_CERTIFICATE_SET
           EVP_PKT_ENC                             R_NO_CERTIFICATE_SPECIFIED
           EVP_PKT_EXCH                            R_NO_CIPHER_LIST
           EVP_PKT_EXP                             R_NO_CIPHER_MATCH
           EVP_PKT_SIGN                            R_NO_PRIVATEKEY
           EVP_PK_DH                               R_NO_PUBLICKEY
           EVP_PK_DSA                              R_NULL_SSL_CTX
           EVP_PK_EC                               R_PEER_DID_NOT_RETURN_A_CERTIFICATE
           EVP_PK_RSA                              R_PEER_ERROR
           FILETYPE_ASN1                           R_PEER_ERROR_CERTIFICATE
           FILETYPE_PEM                            R_PEER_ERROR_NO_CIPHER
           F_CLIENT_CERTIFICATE                    R_PEER_ERROR_UNSUPPORTED_CERTIFICATE_TYPE
           F_CLIENT_HELLO                          R_PUBLIC_KEY_ENCRYPT_ERROR
           F_CLIENT_MASTER_KEY                     R_PUBLIC_KEY_IS_NOT_RSA
           F_D2I_SSL_SESSION                       R_READ_WRONG_PACKET_TYPE
           F_GET_CLIENT_FINISHED                   R_SHORT_READ
           F_GET_CLIENT_HELLO                      R_SSL_SESSION_ID_IS_DIFFERENT
           F_GET_CLIENT_MASTER_KEY                 R_UNABLE_TO_EXTRACT_PUBLIC_KEY
           F_GET_SERVER_FINISHED                   R_UNKNOWN_REMOTE_ERROR_TYPE
           F_GET_SERVER_HELLO                      R_UNKNOWN_STATE
           F_GET_SERVER_VERIFY                     R_X509_LIB
           F_I2D_SSL_SESSION                       SENT_SHUTDOWN
           F_READ_N                                SESSION_ASN1_VERSION
           F_REQUEST_CERTIFICATE                   SESS_CACHE_BOTH
           F_SERVER_HELLO                          SESS_CACHE_CLIENT
           F_SSL_CERT_NEW                          SESS_CACHE_NO_AUTO_CLEAR
           F_SSL_GET_NEW_SESSION                   SESS_CACHE_NO_INTERNAL
           F_SSL_NEW                               SESS_CACHE_NO_INTERNAL_LOOKUP
           F_SSL_READ                              SESS_CACHE_NO_INTERNAL_STORE
           F_SSL_RSA_PRIVATE_DECRYPT               SESS_CACHE_OFF
           F_SSL_RSA_PUBLIC_ENCRYPT                SESS_CACHE_SERVER
           F_SSL_SESSION_NEW                       SESS_CACHE_UPDATE_TIME
           F_SSL_SESSION_PRINT_FP                  SSL2_MT_CLIENT_CERTIFICATE
           F_SSL_SET_FD                            SSL2_MT_CLIENT_FINISHED
           F_SSL_SET_RFD                           SSL2_MT_CLIENT_HELLO
           F_SSL_SET_WFD                           SSL2_MT_CLIENT_MASTER_KEY
           F_SSL_USE_CERTIFICATE                   SSL2_MT_ERROR
           F_SSL_USE_CERTIFICATE_ASN1              SSL2_MT_REQUEST_CERTIFICATE
           F_SSL_USE_CERTIFICATE_FILE              SSL2_MT_SERVER_FINISHED
           F_SSL_USE_PRIVATEKEY                    SSL2_MT_SERVER_HELLO
           F_SSL_USE_PRIVATEKEY_ASN1               SSL2_MT_SERVER_VERIFY
           F_SSL_USE_PRIVATEKEY_FILE               SSL2_VERSION
           F_SSL_USE_RSAPRIVATEKEY                 SSL3_MT_CCS
           F_SSL_USE_RSAPRIVATEKEY_ASN1            SSL3_MT_CERTIFICATE
           F_SSL_USE_RSAPRIVATEKEY_FILE            SSL3_MT_CERTIFICATE_REQUEST
           F_WRITE_PENDING                         SSL3_MT_CERTIFICATE_STATUS
           GEN_DIRNAME                             SSL3_MT_CERTIFICATE_URL
           GEN_DNS                                 SSL3_MT_CERTIFICATE_VERIFY
           GEN_EDIPARTY                            SSL3_MT_CHANGE_CIPHER_SPEC
           GEN_EMAIL                               SSL3_MT_CLIENT_HELLO
           GEN_IPADD                               SSL3_MT_CLIENT_KEY_EXCHANGE
           GEN_OTHERNAME                           SSL3_MT_ENCRYPTED_EXTENSIONS
           GEN_RID                                 SSL3_MT_END_OF_EARLY_DATA
           GEN_URI                                 SSL3_MT_FINISHED
           GEN_X400                                SSL3_MT_HELLO_REQUEST
           LIBRESSL_VERSION_NUMBER                 SSL3_MT_KEY_UPDATE
           MBSTRING_ASC                            SSL3_MT_MESSAGE_HASH
           MBSTRING_BMP                            SSL3_MT_NEWSESSION_TICKET
           MBSTRING_FLAG                           SSL3_MT_NEXT_PROTO
           MBSTRING_UNIV                           SSL3_MT_SERVER_DONE
           MBSTRING_UTF8                           SSL3_MT_SERVER_HELLO
           MIN_RSA_MODULUS_LENGTH_IN_BYTES         SSL3_MT_SERVER_KEY_EXCHANGE
           MODE_ACCEPT_MOVING_WRITE_BUFFER         SSL3_MT_SUPPLEMENTAL_DATA
           MODE_ASYNC                              SSL3_RT_ALERT
           MODE_AUTO_RETRY                         SSL3_RT_APPLICATION_DATA
           MODE_ENABLE_PARTIAL_WRITE               SSL3_RT_CHANGE_CIPHER_SPEC
           MODE_NO_AUTO_CHAIN                      SSL3_RT_HANDSHAKE
           MODE_RELEASE_BUFFERS                    SSL3_RT_HEADER
           NID_OCSP_sign                           SSL3_RT_INNER_CONTENT_TYPE
           NID_SMIMECapabilities                   SSL3_VERSION
           NID_X500                                SSLEAY_BUILT_ON
           NID_X509                                SSLEAY_CFLAGS
           NID_ad_OCSP                             SSLEAY_DIR
           NID_ad_ca_issuers                       SSLEAY_PLATFORM
           NID_algorithm                           SSLEAY_VERSION
           NID_authority_key_identifier            ST_ACCEPT
           NID_basic_constraints                   ST_BEFORE
           NID_bf_cbc                              ST_CONNECT
           NID_bf_cfb64                            ST_INIT
           NID_bf_ecb                              ST_OK
           NID_bf_ofb64                            ST_READ_BODY
           NID_cast5_cbc                           ST_READ_HEADER
           NID_cast5_cfb64                         TLS1_1_VERSION
           NID_cast5_ecb                           TLS1_2_VERSION
           NID_cast5_ofb64                         TLS1_3_VERSION
           NID_certBag                             TLS1_VERSION
           NID_certificate_policies                TLSEXT_STATUSTYPE_ocsp
           NID_client_auth                         TLSEXT_TYPE_application_layer_protocol_negotiation
           NID_code_sign                           TLSEXT_TYPE_cert_type
           NID_commonName                          TLSEXT_TYPE_certificate_authorities
           NID_countryName                         TLSEXT_TYPE_client_authz
           NID_crlBag                              TLSEXT_TYPE_client_cert_type
           NID_crl_distribution_points             TLSEXT_TYPE_client_certificate_url
           NID_crl_number                          TLSEXT_TYPE_compress_certificate
           NID_crl_reason                          TLSEXT_TYPE_cookie
           NID_delta_crl                           TLSEXT_TYPE_early_data
           NID_des_cbc                             TLSEXT_TYPE_ec_point_formats
           NID_des_cfb64                           TLSEXT_TYPE_elliptic_curves
           NID_des_ecb                             TLSEXT_TYPE_encrypt_then_mac
           NID_des_ede                             TLSEXT_TYPE_extended_master_secret
           NID_des_ede3                            TLSEXT_TYPE_key_share
           NID_des_ede3_cbc                        TLSEXT_TYPE_max_fragment_length
           NID_des_ede3_cfb64                      TLSEXT_TYPE_next_proto_neg
           NID_des_ede3_ofb64                      TLSEXT_TYPE_padding
           NID_des_ede_cbc                         TLSEXT_TYPE_post_handshake_auth
           NID_des_ede_cfb64                       TLSEXT_TYPE_psk
           NID_des_ede_ofb64                       TLSEXT_TYPE_psk_kex_modes
           NID_des_ofb64                           TLSEXT_TYPE_quic_transport_parameters
           NID_description                         TLSEXT_TYPE_renegotiate
           NID_desx_cbc                            TLSEXT_TYPE_server_authz
           NID_dhKeyAgreement                      TLSEXT_TYPE_server_cert_type
           NID_dnQualifier                         TLSEXT_TYPE_server_name
           NID_dsa                                 TLSEXT_TYPE_session_ticket
           NID_dsaWithSHA                          TLSEXT_TYPE_signature_algorithms
           NID_dsaWithSHA1                         TLSEXT_TYPE_signature_algorithms_cert
           NID_dsaWithSHA1_2                       TLSEXT_TYPE_signed_certificate_timestamp
           NID_dsa_2                               TLSEXT_TYPE_srp
           NID_email_protect                       TLSEXT_TYPE_status_request
           NID_ext_key_usage                       TLSEXT_TYPE_supported_groups
           NID_ext_req                             TLSEXT_TYPE_supported_versions
           NID_friendlyName                        TLSEXT_TYPE_truncated_hmac
           NID_givenName                           TLSEXT_TYPE_trusted_ca_keys
           NID_hmacWithSHA1                        TLSEXT_TYPE_use_srtp
           NID_id_ad                               TLSEXT_TYPE_user_mapping
           NID_id_ce                               VERIFY_CLIENT_ONCE
           NID_id_kp                               VERIFY_FAIL_IF_NO_PEER_CERT
           NID_id_pbkdf2                           VERIFY_NONE
           NID_id_pe                               VERIFY_PEER
           NID_id_pkix                             VERIFY_POST_HANDSHAKE
           NID_id_qt_cps                           V_OCSP_CERTSTATUS_GOOD
           NID_id_qt_unotice                       V_OCSP_CERTSTATUS_REVOKED
           NID_idea_cbc                            V_OCSP_CERTSTATUS_UNKNOWN
           NID_idea_cfb64                          WRITING
           NID_idea_ecb                            X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT
           NID_idea_ofb64                          X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS
           NID_info_access                         X509_CHECK_FLAG_NEVER_CHECK_SUBJECT
           NID_initials                            X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS
           NID_invalidity_date                     X509_CHECK_FLAG_NO_WILDCARDS
           NID_issuer_alt_name                     X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS
           NID_keyBag                              X509_CRL_VERSION_1
           NID_key_usage                           X509_CRL_VERSION_2
           NID_localKeyID                          X509_FILETYPE_ASN1
           NID_localityName                        X509_FILETYPE_DEFAULT
           NID_md2                                 X509_FILETYPE_PEM
           NID_md2WithRSAEncryption                X509_LOOKUP
           NID_md5                                 X509_PURPOSE_ANY
           NID_md5WithRSA                          X509_PURPOSE_CRL_SIGN
           NID_md5WithRSAEncryption                X509_PURPOSE_NS_SSL_SERVER
           NID_md5_sha1                            X509_PURPOSE_OCSP_HELPER
           NID_mdc2                                X509_PURPOSE_SMIME_ENCRYPT
           NID_mdc2WithRSA                         X509_PURPOSE_SMIME_SIGN
           NID_ms_code_com                         X509_PURPOSE_SSL_CLIENT
           NID_ms_code_ind                         X509_PURPOSE_SSL_SERVER
           NID_ms_ctl_sign                         X509_PURPOSE_TIMESTAMP_SIGN
           NID_ms_efs                              X509_REQ_VERSION_1
           NID_ms_ext_req                          X509_REQ_VERSION_2
           NID_ms_sgc                              X509_REQ_VERSION_3
           NID_name                                X509_TRUST_COMPAT
           NID_netscape                            X509_TRUST_DEFAULT
           NID_netscape_base_url                   X509_TRUST_EMAIL
           NID_netscape_ca_policy_url              X509_TRUST_OBJECT_SIGN
           NID_netscape_ca_revocation_url          X509_TRUST_OCSP_REQUEST
           NID_netscape_cert_extension             X509_TRUST_OCSP_SIGN
           NID_netscape_cert_sequence              X509_TRUST_SSL_CLIENT
           NID_netscape_cert_type                  X509_TRUST_SSL_SERVER
           NID_netscape_comment                    X509_TRUST_TSA
           NID_netscape_data_type                  X509_VERSION_1
           NID_netscape_renewal_url                X509_VERSION_2
           NID_netscape_revocation_url             X509_VERSION_3
           NID_netscape_ssl_server_name            X509_V_ERR_AKID_ISSUER_SERIAL_MISMATCH
           NID_ns_sgc                              X509_V_ERR_AKID_SKID_MISMATCH
           NID_organizationName                    X509_V_ERR_APPLICATION_VERIFICATION
           NID_organizationalUnitName              X509_V_ERR_AUTHORITY_KEY_IDENTIFIER_CRITICAL
           NID_pbeWithMD2AndDES_CBC                X509_V_ERR_CA_BCONS_NOT_CRITICAL
           NID_pbeWithMD2AndRC2_CBC                X509_V_ERR_CA_CERT_MISSING_KEY_USAGE
           NID_pbeWithMD5AndCast5_CBC              X509_V_ERR_CA_KEY_TOO_SMALL
           NID_pbeWithMD5AndDES_CBC                X509_V_ERR_CA_MD_TOO_WEAK
           NID_pbeWithMD5AndRC2_CBC                X509_V_ERR_CERT_CHAIN_TOO_LONG
           NID_pbeWithSHA1AndDES_CBC               X509_V_ERR_CERT_HAS_EXPIRED
           NID_pbeWithSHA1AndRC2_CBC               X509_V_ERR_CERT_NOT_YET_VALID
           NID_pbe_WithSHA1And128BitRC2_CBC        X509_V_ERR_CERT_REJECTED
           NID_pbe_WithSHA1And128BitRC4            X509_V_ERR_CERT_REVOKED
           NID_pbe_WithSHA1And2_Key_TripleDES_CBC  X509_V_ERR_CERT_SIGNATURE_FAILURE
           NID_pbe_WithSHA1And3_Key_TripleDES_CBC  X509_V_ERR_CERT_UNTRUSTED
           NID_pbe_WithSHA1And40BitRC2_CBC         X509_V_ERR_CRL_HAS_EXPIRED
           NID_pbe_WithSHA1And40BitRC4             X509_V_ERR_CRL_NOT_YET_VALID
           NID_pbes2                               X509_V_ERR_CRL_PATH_VALIDATION_ERROR
           NID_pbmac1                              X509_V_ERR_CRL_SIGNATURE_FAILURE
           NID_pkcs                                X509_V_ERR_DANE_NO_MATCH
           NID_pkcs3                               X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT
           NID_pkcs7                               X509_V_ERR_DIFFERENT_CRL_SCOPE
           NID_pkcs7_data                          X509_V_ERR_EC_KEY_EXPLICIT_PARAMS
           NID_pkcs7_digest                        X509_V_ERR_EE_KEY_TOO_SMALL
           NID_pkcs7_encrypted                     X509_V_ERR_EMAIL_MISMATCH
           NID_pkcs7_enveloped                     X509_V_ERR_EMPTY_SUBJECT_ALT_NAME
           NID_pkcs7_signed                        X509_V_ERR_EMPTY_SUBJECT_SAN_NOT_CRITICAL
           NID_pkcs7_signedAndEnveloped            X509_V_ERR_ERROR_IN_CERT_NOT_AFTER_FIELD
           NID_pkcs8ShroudedKeyBag                 X509_V_ERR_ERROR_IN_CERT_NOT_BEFORE_FIELD
           NID_pkcs9                               X509_V_ERR_ERROR_IN_CRL_LAST_UPDATE_FIELD
           NID_pkcs9_challengePassword             X509_V_ERR_ERROR_IN_CRL_NEXT_UPDATE_FIELD
           NID_pkcs9_contentType                   X509_V_ERR_EXCLUDED_VIOLATION
           NID_pkcs9_countersignature              X509_V_ERR_EXTENSIONS_REQUIRE_VERSION_3
           NID_pkcs9_emailAddress                  X509_V_ERR_HOSTNAME_MISMATCH
           NID_pkcs9_extCertAttributes             X509_V_ERR_INVALID_CA
           NID_pkcs9_messageDigest                 X509_V_ERR_INVALID_CALL
           NID_pkcs9_signingTime                   X509_V_ERR_INVALID_EXTENSION
           NID_pkcs9_unstructuredAddress           X509_V_ERR_INVALID_NON_CA
           NID_pkcs9_unstructuredName              X509_V_ERR_INVALID_POLICY_EXTENSION
           NID_private_key_usage_period            X509_V_ERR_INVALID_PURPOSE
           NID_rc2_40_cbc                          X509_V_ERR_IP_ADDRESS_MISMATCH
           NID_rc2_64_cbc                          X509_V_ERR_ISSUER_NAME_EMPTY
           NID_rc2_cbc                             X509_V_ERR_KEYUSAGE_NO_CERTSIGN
           NID_rc2_cfb64                           X509_V_ERR_KEYUSAGE_NO_CRL_SIGN
           NID_rc2_ecb                             X509_V_ERR_KEYUSAGE_NO_DIGITAL_SIGNATURE
           NID_rc2_ofb64                           X509_V_ERR_KU_KEY_CERT_SIGN_INVALID_FOR_NON_CA
           NID_rc4                                 X509_V_ERR_MISSING_AUTHORITY_KEY_IDENTIFIER
           NID_rc4_40                              X509_V_ERR_MISSING_SUBJECT_KEY_IDENTIFIER
           NID_rc5_cbc                             X509_V_ERR_NO_EXPLICIT_POLICY
           NID_rc5_cfb64                           X509_V_ERR_NO_ISSUER_PUBLIC_KEY
           NID_rc5_ecb                             X509_V_ERR_NO_VALID_SCTS
           NID_rc5_ofb64                           X509_V_ERR_OCSP_CERT_UNKNOWN
           NID_ripemd160                           X509_V_ERR_OCSP_VERIFY_FAILED
           NID_ripemd160WithRSA                    X509_V_ERR_OCSP_VERIFY_NEEDED
           NID_rle_compression                     X509_V_ERR_OUT_OF_MEM
           NID_rsa                                 X509_V_ERR_PATHLEN_INVALID_FOR_NON_CA
           NID_rsaEncryption                       X509_V_ERR_PATHLEN_WITHOUT_KU_KEY_CERT_SIGN
           NID_rsadsi                              X509_V_ERR_PATH_LENGTH_EXCEEDED
           NID_safeContentsBag                     X509_V_ERR_PATH_LOOP
           NID_sdsiCertificate                     X509_V_ERR_PERMITTED_VIOLATION
           NID_secretBag                           X509_V_ERR_PROXY_CERTIFICATES_NOT_ALLOWED
           NID_serialNumber                        X509_V_ERR_PROXY_PATH_LENGTH_EXCEEDED
           NID_server_auth                         X509_V_ERR_PROXY_SUBJECT_NAME_VIOLATION
           NID_sha                                 X509_V_ERR_SELF_SIGNED_CERT_IN_CHAIN
           NID_sha1                                X509_V_ERR_SIGNATURE_ALGORITHM_INCONSISTENCY
           NID_sha1WithRSA                         X509_V_ERR_SIGNATURE_ALGORITHM_MISMATCH
           NID_sha1WithRSAEncryption               X509_V_ERR_STORE_LOOKUP
           NID_sha224                              X509_V_ERR_SUBJECT_ISSUER_MISMATCH
           NID_sha224WithRSAEncryption             X509_V_ERR_SUBJECT_KEY_IDENTIFIER_CRITICAL
           NID_sha256                              X509_V_ERR_SUBJECT_NAME_EMPTY
           NID_sha256WithRSAEncryption             X509_V_ERR_SUBTREE_MINMAX
           NID_sha384                              X509_V_ERR_SUITE_B_CANNOT_SIGN_P_384_WITH_P_256
           NID_sha384WithRSAEncryption             X509_V_ERR_SUITE_B_INVALID_ALGORITHM
           NID_sha3_224                            X509_V_ERR_SUITE_B_INVALID_CURVE
           NID_sha3_256                            X509_V_ERR_SUITE_B_INVALID_SIGNATURE_ALGORITHM
           NID_sha3_384                            X509_V_ERR_SUITE_B_INVALID_VERSION
           NID_sha3_512                            X509_V_ERR_SUITE_B_LOS_NOT_ALLOWED
           NID_sha512                              X509_V_ERR_UNABLE_TO_DECODE_ISSUER_PUBLIC_KEY
           NID_sha512WithRSAEncryption             X509_V_ERR_UNABLE_TO_DECRYPT_CERT_SIGNATURE
           NID_sha512_224                          X509_V_ERR_UNABLE_TO_DECRYPT_CRL_SIGNATURE
           NID_sha512_224WithRSAEncryption         X509_V_ERR_UNABLE_TO_GET_CRL
           NID_sha512_256                          X509_V_ERR_UNABLE_TO_GET_CRL_ISSUER
           NID_sha512_256WithRSAEncryption         X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT
           NID_shaWithRSAEncryption                X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY
           NID_shake128                            X509_V_ERR_UNABLE_TO_VERIFY_LEAF_SIGNATURE
           NID_shake256                            X509_V_ERR_UNHANDLED_CRITICAL_CRL_EXTENSION
           NID_stateOrProvinceName                 X509_V_ERR_UNHANDLED_CRITICAL_EXTENSION
           NID_subject_alt_name                    X509_V_ERR_UNNESTED_RESOURCE
           NID_subject_key_identifier              X509_V_ERR_UNSPECIFIED
           NID_surname                             X509_V_ERR_UNSUPPORTED_CONSTRAINT_SYNTAX
           NID_sxnet                               X509_V_ERR_UNSUPPORTED_CONSTRAINT_TYPE
           NID_time_stamp                          X509_V_ERR_UNSUPPORTED_EXTENSION_FEATURE
           NID_title                               X509_V_ERR_UNSUPPORTED_NAME_SYNTAX
           NID_undef                               X509_V_ERR_UNSUPPORTED_SIGNATURE_ALGORITHM
           NID_uniqueIdentifier                    X509_V_FLAG_ALLOW_PROXY_CERTS
           NID_x509Certificate                     X509_V_FLAG_CB_ISSUER_CHECK
           NID_x509Crl                             X509_V_FLAG_CHECK_SS_SIGNATURE
           NID_zlib_compression                    X509_V_FLAG_CRL_CHECK
           NOTHING                                 X509_V_FLAG_CRL_CHECK_ALL
           OCSP_RESPONSE_STATUS_INTERNALERROR      X509_V_FLAG_EXPLICIT_POLICY
           OCSP_RESPONSE_STATUS_MALFORMEDREQUEST   X509_V_FLAG_EXTENDED_CRL_SUPPORT
           OCSP_RESPONSE_STATUS_SIGREQUIRED        X509_V_FLAG_IGNORE_CRITICAL
           OCSP_RESPONSE_STATUS_SUCCESSFUL         X509_V_FLAG_INHIBIT_ANY
           OCSP_RESPONSE_STATUS_TRYLATER           X509_V_FLAG_INHIBIT_MAP
           OCSP_RESPONSE_STATUS_UNAUTHORIZED       X509_V_FLAG_LEGACY_VERIFY
           OPENSSL_BUILT_ON                        X509_V_FLAG_NOTIFY_POLICY
           OPENSSL_CFLAGS                          X509_V_FLAG_NO_ALT_CHAINS
           OPENSSL_CPU_INFO                        X509_V_FLAG_NO_CHECK_TIME
           OPENSSL_DIR                             X509_V_FLAG_PARTIAL_CHAIN
           OPENSSL_ENGINES_DIR                     X509_V_FLAG_POLICY_CHECK
           OPENSSL_FULL_VERSION_STRING             X509_V_FLAG_POLICY_MASK
           OPENSSL_INFO_CONFIG_DIR                 X509_V_FLAG_SUITEB_128_LOS
           OPENSSL_INFO_CPU_SETTINGS               X509_V_FLAG_SUITEB_128_LOS_ONLY
           OPENSSL_INFO_DIR_FILENAME_SEPARATOR     X509_V_FLAG_SUITEB_192_LOS
           OPENSSL_INFO_DSO_EXTENSION              X509_V_FLAG_TRUSTED_FIRST
           OPENSSL_INFO_ENGINES_DIR                X509_V_FLAG_USE_CHECK_TIME
           OPENSSL_INFO_LIST_SEPARATOR             X509_V_FLAG_USE_DELTAS
           OPENSSL_INFO_MODULES_DIR                X509_V_FLAG_X509_STRICT
           OPENSSL_INFO_SEED_SOURCE                X509_V_OK
           OPENSSL_INIT_ADD_ALL_CIPHERS            XN_FLAG_COMPAT
           OPENSSL_INIT_ADD_ALL_DIGESTS            XN_FLAG_DN_REV
           OPENSSL_INIT_ASYNC                      XN_FLAG_DUMP_UNKNOWN_FIELDS
           OPENSSL_INIT_ATFORK                     XN_FLAG_FN_ALIGN
           OPENSSL_INIT_ENGINE_AFALG               XN_FLAG_FN_LN
           OPENSSL_INIT_ENGINE_CAPI                XN_FLAG_FN_MASK
           OPENSSL_INIT_ENGINE_CRYPTODEV           XN_FLAG_FN_NONE
           OPENSSL_INIT_ENGINE_DYNAMIC             XN_FLAG_FN_OID
           OPENSSL_INIT_ENGINE_OPENSSL             XN_FLAG_FN_SN
           OPENSSL_INIT_ENGINE_PADLOCK             XN_FLAG_MULTILINE
           OPENSSL_INIT_ENGINE_RDRAND              XN_FLAG_ONELINE
           OPENSSL_INIT_LOAD_CONFIG                XN_FLAG_RFC2253
           OPENSSL_INIT_LOAD_CRYPTO_STRINGS        XN_FLAG_SEP_COMMA_PLUS
           OPENSSL_INIT_LOAD_SSL_STRINGS           XN_FLAG_SEP_CPLUS_SPC
           OPENSSL_INIT_NO_ADD_ALL_CIPHERS         XN_FLAG_SEP_MASK
           OPENSSL_INIT_NO_ADD_ALL_DIGESTS         XN_FLAG_SEP_MULTILINE
           OPENSSL_INIT_NO_ATEXIT                  XN_FLAG_SEP_SPLUS_SPC
           OPENSSL_INIT_NO_LOAD_CONFIG             XN_FLAG_SPC_EQ

   INTERNAL ONLY functions (do not use these)
       The following functions  are  not  intended  for  use  from  outside  of
       Net::SSLeay  module.   They might be removed, renamed or changed without
       prior notice in future version.

       Simply DO NOT USE THEM!

       •   hello

       •   blength

       •   constant

EXAMPLES
       One very good example to look at is the implementation  of  sslcat()  in
       the "SSLeay.pm" file.

       The  following is a simple SSLeay client (with too little error checking
       :-(

           #!/usr/bin/perl
           use Socket;
           use Net::SSLeay qw(die_now die_if_ssl_error) ;
           Net::SSLeay::load_error_strings();
           Net::SSLeay::SSLeay_add_ssl_algorithms();
           Net::SSLeay::randomize();

           ($dest_serv, $port, $msg) = @ARGV;      # Read command line
           $port = getservbyname ($port, 'tcp') unless $port =~ /^\d+$/;
           $dest_ip = gethostbyname ($dest_serv);
           $dest_serv_params  = sockaddr_in($port, $dest_ip);

           socket  (S, &AF_INET, &SOCK_STREAM, 0)  or die "socket: $!";
           connect (S, $dest_serv_params)          or die "connect: $!";
           select  (S); $| = 1; select (STDOUT);   # Eliminate STDIO buffering

           # The network connection is now open, lets fire up SSL

           $ctx = Net::SSLeay::CTX_new() or die_now("Failed to create SSL_CTX $!");
           Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL)
                or die_if_ssl_error("ssl ctx set options");
           $ssl = Net::SSLeay::new($ctx) or die_now("Failed to create SSL $!");
           Net::SSLeay::set_fd($ssl, fileno(S));   # Must use fileno
           $res = Net::SSLeay::connect($ssl) and die_if_ssl_error("ssl connect");
           print "Cipher `" . Net::SSLeay::get_cipher($ssl) . "'\n";

           # Exchange data

           $res = Net::SSLeay::write($ssl, $msg);  # Perl knows how long $msg is
           die_if_ssl_error("ssl write");
           CORE::shutdown S, 1;  # Half close --> No more output, sends EOF to server
           $got = Net::SSLeay::read($ssl);         # Perl returns undef on failure
           die_if_ssl_error("ssl read");
           print $got;

           Net::SSLeay::free ($ssl);               # Tear down connection
           Net::SSLeay::CTX_free ($ctx);
           close S;

       The following is a simple SSLeay echo server (non forking):

           #!/usr/bin/perl -w
           use Socket;
           use Net::SSLeay qw(die_now die_if_ssl_error);
           Net::SSLeay::load_error_strings();
           Net::SSLeay::SSLeay_add_ssl_algorithms();
           Net::SSLeay::randomize();

           $our_ip = "\0\0\0\0"; # Bind to all interfaces
           $port = 1235;
           $sockaddr_template = 'S n a4 x8';
           $our_serv_params = pack ($sockaddr_template, &AF_INET, $port, $our_ip);

           socket (S, &AF_INET, &SOCK_STREAM, 0)  or die "socket: $!";
           bind (S, $our_serv_params)             or die "bind:   $!";
           listen (S, 5)                          or die "listen: $!";
           $ctx = Net::SSLeay::CTX_new ()         or die_now("CTX_new ($ctx): $!");
           Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL)
                or die_if_ssl_error("ssl ctx set options");

           # Following will ask password unless private key is not encrypted
           Net::SSLeay::CTX_use_RSAPrivateKey_file ($ctx, 'plain-rsa.pem',
                                                    &Net::SSLeay::FILETYPE_PEM);
           die_if_ssl_error("private key");
           Net::SSLeay::CTX_use_certificate_file ($ctx, 'plain-cert.pem',
                                                   &Net::SSLeay::FILETYPE_PEM);
           die_if_ssl_error("certificate");

           while (1) {
               print "Accepting connections...\n";
               ($addr = accept (NS, S))           or die "accept: $!";
               select (NS); $| = 1; select (STDOUT);  # Piping hot!

               ($af,$client_port,$client_ip) = unpack($sockaddr_template,$addr);
               @inetaddr = unpack('C4',$client_ip);
               print "$af connection from " .
               join ('.', @inetaddr) . ":$client_port\n";

               # We now have a network connection, lets fire up SSLeay...

               $ssl = Net::SSLeay::new($ctx)      or die_now("SSL_new ($ssl): $!");
               Net::SSLeay::set_fd($ssl, fileno(NS));

               $err = Net::SSLeay::accept($ssl) and die_if_ssl_error('ssl accept');
               print "Cipher `" . Net::SSLeay::get_cipher($ssl) . "'\n";

               # Connected. Exchange some data.

               $got = Net::SSLeay::read($ssl);     # Returns undef on fail
               die_if_ssl_error("ssl read");
               print "Got `$got' (" . length ($got) . " chars)\n";

               Net::SSLeay::write ($ssl, uc ($got)) or die "write: $!";
               die_if_ssl_error("ssl write");

               Net::SSLeay::free ($ssl);           # Tear down connection
               close NS;
           }

       Yet another echo server. This one  runs  from  "/etc/inetd.conf"  so  it
       avoids  all  the socket code overhead. Only caveat is opening an rsa key
       file - it had better be without any encryption or else it will not  know
       where  to  ask for the password. Note how "STDIN" and "STDOUT" are wired
       to SSL.

           #!/usr/bin/perl
           # /etc/inetd.conf
           #    ssltst stream tcp nowait root /path/to/server.pl server.pl
           # /etc/services
           #    ssltst        1234/tcp

           use Net::SSLeay qw(die_now die_if_ssl_error);
           Net::SSLeay::load_error_strings();
           Net::SSLeay::SSLeay_add_ssl_algorithms();
           Net::SSLeay::randomize();

           chdir '/key/dir' or die "chdir: $!";
           $| = 1;  # Piping hot!
           open LOG, ">>/dev/console" or die "Can't open log file $!";
           select LOG; print "server.pl started\n";

           $ctx = Net::SSLeay::CTX_new()     or die_now "CTX_new ($ctx) ($!)";
           $ssl = Net::SSLeay::new($ctx)     or die_now "new ($ssl) ($!)";
           Net::SSLeay::set_options($ssl, &Net::SSLeay::OP_ALL)
               and die_if_ssl_error("ssl set options");

           # We get already open network connection from inetd, now we just
           # need to attach SSLeay to STDIN and STDOUT
           Net::SSLeay::set_rfd($ssl, fileno(STDIN));
           Net::SSLeay::set_wfd($ssl, fileno(STDOUT));

           Net::SSLeay::use_RSAPrivateKey_file ($ssl, 'plain-rsa.pem',
                                                Net::SSLeay::FILETYPE_PEM);
           die_if_ssl_error("private key");
           Net::SSLeay::use_certificate_file ($ssl, 'plain-cert.pem',
                                              Net::SSLeay::FILETYPE_PEM);
           die_if_ssl_error("certificate");

           Net::SSLeay::accept($ssl) and die_if_ssl_err("ssl accept: $!");
           print "Cipher `" . Net::SSLeay::get_cipher($ssl) . "'\n";

           $got = Net::SSLeay::read($ssl);
           die_if_ssl_error("ssl read");
           print "Got `$got' (" . length ($got) . " chars)\n";

           Net::SSLeay::write ($ssl, uc($got)) or die "write: $!";
           die_if_ssl_error("ssl write");

           Net::SSLeay::free ($ssl);         # Tear down the connection
           Net::SSLeay::CTX_free ($ctx);
           close LOG;

       There are also  a  number  of  example/test  programs  in  the  examples
       directory:

           sslecho.pl   -  A simple server, not unlike the one above
           minicli.pl   -  Implements a client using low level SSLeay routines
           sslcat.pl    -  Demonstrates using high level sslcat utility function
           get_page.pl  -  Is a utility for getting html pages from secure servers
           callback.pl  -  Demonstrates certificate verification and callback usage
           stdio_bulk.pl       - Does SSL over Unix pipes
           ssl-inetd-serv.pl   - SSL server that can be invoked from inetd.conf
           httpd-proxy-snif.pl - Utility that allows you to see how a browser
                                 sends https request to given server and what reply
                                 it gets back (very educative :-)
           makecert.pl  -  Creates a self signed cert (does not use this module)

INSTALLATION
       See  README  and README.* in the distribution directory for installation
       guidance on a variety of platforms.

LIMITATIONS
       Net::SSLeay::read() uses an internal buffer of 32KB, thus no single read
       will return more. In practice one read returns  much  less,  usually  as
       much  as fits in one network packet. To work around this, you should use
       a loop like this:

           $reply = '';
           while ($got = Net::SSLeay::read($ssl)) {
               last if print_errs('SSL_read');
               $reply .= $got;
           }

       Although there is no built-in limit in Net::SSLeay::write(), the network
       packet size limitation applies here as well, thus use:

           $written = 0;

           while ($written < length($message)) {
               $written += Net::SSLeay::write($ssl, substr($message, $written));
               last if print_errs('SSL_write');
           }

       Or alternatively you can just use the following convenience functions:

           Net::SSLeay::ssl_write_all($ssl, $message) or die "ssl write failure";
           $got = Net::SSLeay::ssl_read_all($ssl) or die "ssl read failure";

KNOWN BUGS AND CAVEATS
       LibreSSL  versions  in  the  3.1  -  3.3  series  contain  a   TLS   1.3
       implementation  that is not fully compatible with the libssl API, but is
       still advertised during  protocol  auto-negotiation.  If  you  encounter
       problems  or  unexpected  behaviour  with  SSL  or SSL_CTX objects whose
       protocol version was automatically negotiated and libssl is provided  by
       any  of  these  versions  of  LibreSSL,  it  could  be because the peers
       negotiated to use TLS 1.3 - try setting the maximum protocol version  to
       TLS      1.2      (via      Net::SSLeay::set_max_proto_version()      or
       Net::SSLeay::CTX_set_max_proto_version())   before   establishing    the
       connection.   The  first  stable  LibreSSL  version with a fully libssl-
       compatible TLS 1.3 implementation is 3.4.1.

       An OpenSSL  bug  CVE-2015-0290  "OpenSSL  Multiblock  Corrupted  Pointer
       Issue"  can  cause POST requests of over 90kB to fail or crash. This bug
       is reported to be fixed in OpenSSL 1.0.2a.

       Autoloader emits a

           Argument "xxx" isn't numeric in entersub at blib/lib/Net/SSLeay.pm'

       warning if die_if_ssl_error is made autoloadable. If you figure out why,
       drop me a line.

       Callback set using SSL_set_verify() does not appear to  work.  This  may
       well  be  an  openssl  problem (e.g. see "ssl/ssl_lib.c" line 1029). Try
       using SSL_CTX_set_verify() instead and do not be surprised if even  this
       stops working in future versions.

       Callback  and  certificate  verification  stuff  is generally too little
       tested.

       Random numbers are not initialized randomly enough, especially if you do
       not  have  "/dev/random"  and/or  "/dev/urandom"  (such  as  in  Solaris
       platforms  -  but  it's  been  suggested that cryptorand daemon from the
       SUNski package solves this). In this case you should  investigate  third
       party  software  that  can emulate these devices, e.g. by way of a named
       pipe to some program.

       Another  gotcha  with  random  number   initialization   is   randomness
       depletion.  This  phenomenon,  which  has  been extensively discussed in
       OpenSSL, Apache-SSL, and Apache-mod_ssl forums, can cause your script to
       block if you use "/dev/random" or  to  operate  insecurely  if  you  use
       "/dev/urandom".  What  happens is that when too much randomness is drawn
       from  the  operating  system's  randomness  pool  then  randomness   can
       temporarily be unavailable. "/dev/random" solves this problem by waiting
       until  enough randomness can be gathered - and this can take a long time
       since blocking  reduces  activity  in  the  machine  and  less  activity
       provides  less  random  events: a vicious circle.  "/dev/urandom" solves
       this dilemma more pragmatically by simply returning predictable "random"
       numbers. Some "/dev/urandom" emulation software however  actually  seems
       to implement "/dev/random" semantics. Caveat emptor.

       I've   been   pointed   to   two   such   daemons   by   Mik   Firestone
       <mik@@speed.stdio._com> who has used them on Solaris 8:

       1.  Entropy Gathering Daemon (EGD) at <https://egd.sourceforge.net/>

       2.  Pseudo-random    number     generating     daemon     (PRNGD)     at
           <https://prngd.sourceforge.net/>

       If  you  are using the low level API functions to communicate with other
       SSL implementations, you would do well to call

           Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL)
               or die_if_ssl_error("ssl ctx set options");

       to cope with some well know bugs in some other SSL implementations.  The
       high level API functions always set all known compatibility options.

       Sometimes sslcat() (and the high level HTTPS functions that build on it)
       is  too  fast  in signaling the EOF to legacy HTTPS servers. This causes
       the server to return empty page. To work around this problem you can set
       the global variable

           $Net::SSLeay::slowly = 1;   # Add sleep so broken servers can keep up

       HTTP/1.1 is not supported. Specifically this module  does  not  know  to
       issue  or serve multiple http requests per connection. This is a serious
       shortcoming, but using the SSL session cache on  your  server  helps  to
       alleviate the CPU load somewhat.

       As  of  version  1.09  many newer OpenSSL auxiliary functions were added
       (from  "REM_AUTOMATICALLY_GENERATED_1_09"   onwards   in   "SSLeay.xs").
       Unfortunately I have not had any opportunity to test these. Some of them
       are  trivial  enough  that  I  believe they "just work", but others have
       rather complex interfaces with function pointers and all. In these cases
       you should proceed wit great caution.

       This module defaults to using  OpenSSL  automatic  protocol  negotiation
       code  for  automatically  detecting  the version of the SSL/TLS protocol
       that the other end talks. With most web servers this  works  just  fine,
       but  once  in  a while I get complaints from people that the module does
       not work with some web servers. Usually this can be solved by explicitly
       setting the protocol version, e.g.

           $Net::SSLeay::ssl_version = 2;  # Insist on SSLv2
           $Net::SSLeay::ssl_version = 3;  # Insist on SSLv3
           $Net::SSLeay::ssl_version = 10; # Insist on TLSv1
           $Net::SSLeay::ssl_version = 11; # Insist on TLSv1.1
           $Net::SSLeay::ssl_version = 12; # Insist on TLSv1.2
           $Net::SSLeay::ssl_version = 13; # Insist on TLSv1.3

       Although the autonegotiation is nice to have, the SSL standards  do  not
       formally  specify any such mechanism. Most of the world has accepted the
       SSLeay/OpenSSL way of doing it as the de facto standard. But for the few
       that think  differently,  you  have  to  explicitly  speak  the  correct
       version.  This  is  not  really  a  bug,  but rather a deficiency in the
       standards. If a site refuses to respond or sends back  some  nonsensical
       error codes (at the SSL handshake level), try this option before mailing
       me.

       On  some systems, OpenSSL may be compiled without support for SSLv2.  If
       this is the case, Net::SSLeay will warn if ssl_version has been  set  to
       2.

       The  high  level  API returns the certificate of the peer, thus allowing
       one to check what certificate was supplied. However, you  will  only  be
       able to check the certificate after the fact, i.e. you already sent your
       form data by the time you find out that you did not trust them, oops.

       So,  while  being  able to know the certificate after the fact is surely
       useful, the security minded would still choose to do the connection  and
       certificate  verification  first  and  only  then exchange data with the
       site. Currently none of the high level API functions do this,  thus  you
       would  have to program it using the low level API. A good place to start
       is to see how the Net::SSLeay::http_cat() function is implemented.

       The high level  API  functions  use  a  global  file  handle  "SSLCAT_S"
       internally.  This really should not be a problem because there is no way
       to interleave the high level API functions, unless you use threads  (but
       threads  are  not  very well supported in perl anyway). However, you may
       run into problems if you call  undocumented  internal  functions  in  an
       interleaved  fashion.  The  best solution is to "require Net::SSLeay" in
       one thread after all the threads have been created.

DIAGNOSTICS
       Random number generator not seeded!!!
           (W) This warning indicates that randomize() was  not  able  to  read
           "/dev/random"  or  "/dev/urandom", possibly because your system does
           not have them or they are differently named. You can still use  SSL,
           but the encryption will not be as strong.

       open_tcp_connection: destination host not found:`server' (port 123) ($!)
           Name lookup for host named "server" failed.

       open_tcp_connection: failed `server', 123 ($!)
           The name was resolved, but establishing the TCP connection failed.

       msg 123: 1 - error:140770F8:SSL routines:SSL23_GET_SERVER_HELLO:unknown
       proto
           SSLeay  error  string. The first number (123) is the PID, the second
           number (1) indicates the position of the  error  message  in  SSLeay
           error  stack.   You  often  see  a  pile of these messages as errors
           cascade.

       msg 123: 1 - error:02001002::lib(2) :func(1) :reason(2)
           The same as above,  but  you  didn't  call  load_error_strings()  so
           SSLeay  couldn't verbosely explain the error. You can still find out
           what it means with this command:

               /usr/local/ssl/bin/ssleay errstr 02001002

       Password is being asked for private key
           This is normal behaviour if your private key  is  encrypted.  Either
           you  have  to  supply the password or you have to use an unencrypted
           private key. Scan OpenSSL.org for the FAQ that explains  how  to  do
           this  (or just study examples/makecert.pl which is used during "make
           test" to do just that).

SECURITY
       You can mitigate some of the  security  vulnerabilities  that  might  be
       present in your SSL/TLS application:

   BEAST Attack
       •   <https://web.archive.org/web/20140424022931/https://blogs.cisco.com/security/beat-the-beast-with-tls>

       •   <https://community.qualys.com/blogs/securitylabs/2011/10/17/mitigating-the-beast-attack-on-tls>

       •   <https://blog.zoller.lu/2011/09/beast-summary-tls-cbc-countermeasures.html>

       The  BEAST  attack  relies  on a weakness in the way CBC mode is used in
       SSL/TLS.  In OpenSSL  versions  0.9.6d  and  later,  the  protocol-level
       mitigation  is  enabled by default, thus making it not vulnerable to the
       BEAST attack.

       Solutions:

       •   Compile  with  OpenSSL  versions  0.9.6d  or  later,  which  enables
           SSL_OP_ALL by default

       •   Ensure  SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS  is  not enabled (its not
           enabled by default)

       •   Don't support SSLv2, SSLv3

       •   Actively   control   the   ciphers   your   server   supports   with
           set_cipher_list:

           Net::SSLeay::set_cipher_list($ssl, 'RC4-SHA:HIGH:!ADH');

   Session Resumption
       •   <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_options.html>

       The SSL Labs vulnerability test on your SSL server might report in red:

       Session resumption      No (IDs assigned but not accepted)

       This  report is not really bug or a vulnerability, since the server will
       not accept session resumption requests.  However, you can  prevent  this
       noise in the report by disabling the session cache altogether:

           Net::SSLeay::CTX_set_session_cache_mode($ssl_ctx, Net::SSLeay::SESS_CACHE_OFF());
           # Use 0 if you don't have SESS_CACHE_OFF constant.

   Secure Renegotiation and DoS Attack
       •   <https://community.qualys.com/blogs/securitylabs/2011/10/31/tls-renegotiation-and-denial-of-service-attacks>

       This is not a "security flaw," it is more of a DoS vulnerability.

       Solutions:

       •   Do not support SSLv2

       •   Do not set the SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION option

       •   Compile with OpenSSL 0.9.8m or later

BUGS
       If  you  encounter a problem with this module that you believe is a bug,
       please create a new issue  <https://github.com/radiator-software/p5-net-
       ssleay/issues/new> in the Net-SSLeay GitHub repository. Please make sure
       your bug report includes the following information:

       •   the code you are trying to run;

       •   your operating system name and version;

       •   the output of "perl -V";

       •   the version of OpenSSL or LibreSSL you are using.

AUTHOR
       Originally written by Sampo Kellomäki.

       Maintained by Florian Ragwitz between November 2005 and January 2010.

       Maintained by Mike McCauley between November 2005 and June 2018.

       Maintained by Tuure Vartiainen between June 2018 and July 2018.

       Maintained by Chris Novakovic and Heikki Vatiainen since June 2018.

COPYRIGHT
       Copyright (c) 1996-2003 Sampo Kellomäki <sampo@iki.fi>

       Copyright (c) 2005-2010 Florian Ragwitz <rafl@debian.org>

       Copyright (c) 2005-2018 Mike McCauley <mikem@airspayce.com>

       Copyright (c) 2018 Tuure Vartiainen <vartiait@radiatorsoftware.com>

       Copyright (c) 2018- Chris Novakovic <chris@chrisn.me.uk>

       Copyright (c) 2018- Heikki Vatiainen <hvn@radiatorsoftware.com>

       All rights reserved.

LICENSE
       This module is released under the terms of the Artistic License 2.0. For
       details,  see  the  "LICENSE"  file distributed with Net-SSLeay's source
       code.

SEE ALSO
           Net::SSLeay::Handle                      - File handle interface
           ./examples                               - Example servers and a clients
           <https://www.openssl.org/>               - OpenSSL source, documentation, etc
           openssl-users-request@openssl.org        - General OpenSSL mailing list
           <https://www.ietf.org/rfc/rfc2246.txt>   - TLS 1.0 specification
           <https://www.w3c.org>                    - HTTP specifications
           <https://www.ietf.org/rfc/rfc2617.txt>   - How to send password
           <https://egd.sourceforge.net/>           - Entropy Gathering Daemon (EGD)
           <https://prngd.sourceforge.net/>         - pseudo-random number generating daemon (PRNGD)
           perl(1)
           perlref(1)
           perllol(1)
           perldoc ~openssl/doc/ssl/SSL_CTX_set_verify.pod

perl v5.40.1                       2025-02-19                  Net::SSLeay(3pm)

Generated by dwww version 1.16 on Tue Dec 16 05:35:52 CET 2025.