CONFIG(5SSL) OpenSSL CONFIG(5SSL)
NAME
config - OpenSSL CONF library configuration files
DESCRIPTION
This page documents the syntax of OpenSSL configuration files, as parsed
by NCONF_load(3) and related functions. This format is used by many of
the OpenSSL commands, and to initialize the libraries when used by any
application.
The first part describes the general syntax of the configuration files,
and subsequent sections describe the semantics of individual modules.
Other modules are described in fips_config(5) and x509v3_config(5). The
syntax for defining ASN.1 values is described in ASN1_generate_nconf(3).
SYNTAX
A configuration file is a series of lines. Blank lines, and whitespace
between the elements of a line, have no significance. A comment starts
with a # character; the rest of the line is ignored. If the # is the
first non-space character in a line, the entire line is ignored.
Directives
Two directives can be used to control the parsing of configuration
files: .include and .pragma.
For compatibility with older versions of OpenSSL, an equal sign after
the directive will be ignored. Older versions will treat it as an
assignment, so care should be taken if the difference in semantics is
important.
A file can include other files using the include syntax:
.include [=] pathname
If pathname is a simple filename, that file is included directly at that
point. Included files can have .include statements that specify other
files. If pathname is a directory, all files within that directory that
have a ".cnf" or ".conf" extension will be included. (This is only
available on systems with POSIX IO support.) Any sub-directories found
inside the pathname are ignored. Similarly, if a file is opened while
scanning a directory, and that file has an .include directive that
specifies a directory, that is also ignored.
As a general rule, the pathname should be an absolute path; this can be
enforced with the abspath and includedir pragmas, described below. The
environment variable OPENSSL_CONF_INCLUDE, if it exists, is prepended to
all relative pathnames. If the pathname is still relative, it is
interpreted based on the current working directory.
To require all file inclusions to name absolute paths, use the following
directive:
.pragma [=] abspath:value
The default behavior, where the value is false or off, is to allow
relative paths. To require all .include pathnames to be absolute paths,
use a value of true or on.
In these files, the dollar sign, $, is used to reference a variable, as
described below. On some platforms, however, it is common to treat $ as
a regular character in symbol names. Supporting this behavior can be
done with the following directive:
.pragma [=] dollarid:value
The default behavior, where the value is false or off, is to treat the
dollarsign as indicating a variable name; "foo$bar" is interpreted as
"foo" followed by the expansion of the variable "bar". If value is true
or on, then "foo$bar" is a single seven-character name and variable
expansions must be specified using braces or parentheses.
.pragma [=] includedir:value
If a relative pathname is specified in the .include directive, and the
OPENSSL_CONF_INCLUDE environment variable doesn't exist, then the value
of the includedir pragma, if it exists, is prepended to the pathname.
Settings
A configuration file is divided into a number of sections. A section
begins with the section name in square brackets, and ends when a new
section starts, or at the end of the file. The section name can consist
of alphanumeric characters and underscores. Whitespace between the name
and the brackets is removed.
The first section of a configuration file is special and is referred to
as the default section. This section is usually unnamed and spans from
the start of file until the first named section. When a name is being
looked up, it is first looked up in the current or named section, and
then the default section if necessary.
The environment is mapped onto a section called ENV.
Within a section are a series of name/value assignments, described in
more detail below. As a reminder, the square brackets shown in this
example are required, not optional:
[ section ]
name1 = This is value1
name2 = Another value
...
[ newsection ]
name1 = New value1
name3 = Value 3
The name can contain any alphanumeric characters as well as a few
punctuation symbols such as . , ; and _. Whitespace after the name and
before the equal sign is ignored.
If a name is repeated in the same section, then all but the last value
are ignored. In certain circumstances, such as with Certificate DNs, the
same field may occur multiple times. In order to support this, commands
like openssl-req(1) ignore any leading text that is preceded with a
period. For example:
1.OU = First OU
2.OU = Second OU
The value consists of the string following the = character until end of
line with any leading and trailing whitespace removed.
The value string undergoes variable expansion. The text $var or "${var}"
inserts the value of the named variable from the current section. To
use a value from another section use $section::name or
"${section::name}". By using $ENV::name, the value of the specified
environment variable will be substituted.
Variables must be defined before their value is referenced, otherwise an
error is flagged and the file will not load. This can be worked around
by specifying a default value in the default section before the variable
is used.
Any name/value settings in an ENV section are available to the
configuration file, but are not propagated to the environment.
It is an error if the value ends up longer than 64k.
It is possible to escape certain characters by using a single ' or
double " quote around the value, or using a backslash \ before the
character, By making the last character of a line a \ a value string can
be spread across multiple lines. In addition the sequences \n, \r, \b
and \t are recognized.
The expansion and escape rules as described above that apply to value
also apply to the pathname of the .include directive.
OPENSSL LIBRARY CONFIGURATION
The sections below use the informal term module to refer to a part of
the OpenSSL functionality. This is not the same as the formal term FIPS
module, for example.
The OpenSSL configuration looks up the value of openssl_conf in the
default section and takes that as the name of a section that specifies
how to configure any modules in the library. It is not an error to leave
any module in its default configuration. An application can specify a
different name by calling CONF_modules_load_file(), for example,
directly.
OpenSSL also looks up the value of config_diagnostics. If this exists
and has a nonzero numeric value, any error suppressing flags passed to
CONF_modules_load() will be ignored. This is useful for diagnosing
misconfigurations but its use in production requires additional
consideration. With this option enabled, a configuration error will
completely prevent access to a service. Without this option and in the
presence of a configuration error, access will be allowed but the
desired configuration will not be used.
# These must be in the default section
config_diagnostics = 1
openssl_conf = openssl_init
[openssl_init]
oid_section = oids
providers = providers
alg_section = evp_properties
ssl_conf = ssl_configuration
engines = engines
random = random
[oids]
... new oids here ...
[providers]
... provider stuff here ...
[evp_properties]
... EVP properties here ...
[ssl_configuration]
... SSL/TLS configuration properties here ...
[engines]
... engine properties here ...
[random]
... random properties here ...
The semantics of each module are described below. The phrase "in the
initialization section" refers to the section identified by the
openssl_conf or other name (given as openssl_init in the example above).
The examples below assume the configuration above is used to specify the
individual sections.
ASN.1 Object Identifier Configuration
The name oid_section in the initialization section names the section
containing name/value pairs of OID's. The name is the short name; the
value is an optional long name followed by a comma, and the numeric
value. While some OpenSSL commands have their own section for
specifying OID's, this section makes them available to all commands and
applications.
[oids]
shortName = a very long OID name, 1.2.3.4
newoid1 = 1.2.3.4.1
some_other_oid = 1.2.3.5
If a full configuration with the above fragment is in the file
example.cnf, then the following command line:
OPENSSL_CONF=example.cnf openssl asn1parse -genstr OID:1.2.3.4.1
will output:
0:d=0 hl=2 l= 4 prim: OBJECT :newoid1
showing that the OID "newoid1" has been added as "1.2.3.4.1".
Provider Configuration
The name providers in the initialization section names the section
containing cryptographic provider configuration. The name/value
assignments in this section each name a provider, and point to the
configuration section for that provider. The provider-specific section
is used to specify how to load the module, activate it, and set other
parameters.
Within a provider section, the following names have meaning:
identity
This is used to specify an alternate name, overriding the default
name specified in the list of providers. For example:
[providers]
foo = foo_provider
[foo_provider]
identity = my_fips_module
module
Specifies the pathname of the module (typically a shared library) to
load.
activate
If present and set to one of the values yes, on, true or 1, then the
associated provider will be activated. Conversely, setting this
value to no, off, false, or 0 will prevent the provider from being
activated. Settings can be given in lower or uppercase. Setting
activate to any other setting, or omitting a setting value will
result in an error.
= item soft_load
If enabled, informs the library to clear the error stack on failure
to activate requested provider. A value of 1, yes, true or on (in
lower or uppercase) will activate this setting, while a value of 0,
no, false, or off (again in lower or uppercase) will disable this
setting. Any other value will produce an error. Note this setting
defaults to off if not provided
All parameters in the section as well as sub-sections are made available
to the provider.
Default provider and its activation
If no providers are activated explicitly, the default one is activated
implicitly. See OSSL_PROVIDER-default(7) for more details.
If you add a section explicitly activating any other provider(s), you
most probably need to explicitly activate the default provider,
otherwise it becomes unavailable in openssl. It may make the system
remotely unavailable.
EVP Configuration
The name alg_section in the initialization section names the section
containing algorithmic properties when using the EVP API.
Within the algorithm properties section, the following names have
meaning:
default_properties
The value may be anything that is acceptable as a property query
string for EVP_set_default_properties().
fips_mode (deprecated)
The value is a boolean that can be yes or no. If the value is yes,
this is exactly equivalent to:
default_properties = fips=yes
If the value is no, nothing happens. Using this name is deprecated,
and if used, it must be the only name in the section.
SSL Configuration
The name ssl_conf in the initialization section names the section
containing the list of SSL/TLS configurations. As with the providers,
each name in this section identifies a section with the configuration
for that name. For example:
[ssl_configuration]
server = server_tls_config
client = client_tls_config
system_default = tls_system_default
[server_tls_config]
... configuration for SSL/TLS servers ...
[client_tls_config]
... configuration for SSL/TLS clients ...
The configuration name system_default has a special meaning. If it
exists, it is applied whenever an SSL_CTX object is created. For
example, to impose system-wide minimum TLS and DTLS protocol versions:
[tls_system_default]
MinProtocol = TLSv1.2
MinProtocol = DTLSv1.2
The minimum TLS protocol is applied to SSL_CTX objects that are TLS-
based, and the minimum DTLS protocol to those are DTLS-based. The same
applies also to maximum versions set with MaxProtocol.
Each configuration section consists of name/value pairs that are parsed
by SSL_CONF_cmd(3), which will be called by SSL_CTX_config() or
SSL_config(), appropriately. Note that any characters before an initial
dot in the configuration section are ignored, so that the same command
can be used multiple times. This probably is most useful for loading
different key types, as shown here:
[server_tls_config]
RSA.Certificate = server-rsa.pem
ECDSA.Certificate = server-ecdsa.pem
Engine Configuration
The name engines in the initialization section names the section
containing the list of ENGINE configurations. As with the providers,
each name in this section identifies an engine with the configuration
for that engine. The engine-specific section is used to specify how to
load the engine, activate it, and set other parameters.
Within an engine section, the following names have meaning:
engine_id
This is used to specify an alternate name, overriding the default
name specified in the list of engines. If present, it must be first.
For example:
[engines]
foo = foo_engine
[foo_engine]
engine_id = myfoo
dynamic_path
This loads and adds an ENGINE from the given path. It is equivalent
to sending the ctrls SO_PATH with the path argument followed by
LIST_ADD with value 2 and LOAD to the dynamic ENGINE. If this is
not the required behaviour then alternative ctrls can be sent
directly to the dynamic ENGINE using ctrl commands.
init
This specifies whether to initialize the ENGINE. If the value is 0
the ENGINE will not be initialized, if the value is 1 an attempt is
made to initialize the ENGINE immediately. If the init command is
not present then an attempt will be made to initialize the ENGINE
after all commands in its section have been processed.
default_algorithms
This sets the default algorithms an ENGINE will supply using the
function ENGINE_set_default_string().
All other names are taken to be the name of a ctrl command that is sent
to the ENGINE, and the value is the argument passed with the command.
The special value EMPTY means no value is sent with the command. For
example:
[engines]
foo = foo_engine
[foo_engine]
dynamic_path = /some/path/fooengine.so
some_ctrl = some_value
default_algorithms = ALL
other_ctrl = EMPTY
Random Configuration
The name random in the initialization section names the section
containing the random number generator settings.
Within the random section, the following names have meaning:
random
This is used to specify the random bit generator. For example:
[random]
random = CTR-DRBG
The available random bit generators are:
CTR-DRBG
HASH-DRBG
HMAC-DRBG
cipher
This specifies what cipher a CTR-DRBG random bit generator will use.
Other random bit generators ignore this name. The default value is
AES-256-CTR.
digest
This specifies what digest the HASH-DRBG or HMAC-DRBG random bit
generators will use. Other random bit generators ignore this name.
properties
This sets the property query used when fetching the random bit
generator and any underlying algorithms.
seed
This sets the randomness source that should be used. By default
SEED-SRC will be used outside of the FIPS provider. The FIPS
provider uses call backs to access the same randomness sources from
outside the validated boundary.
seed_properties
This sets the property query used when fetching the randomness
source.
random_provider
This sets the provider to use for the RAND_bytes(3) calls instead of
the built-in entropy sources. It defaults to "fips". If the named
provider is not loaded, the built-in entropy sources will be used.
EXAMPLES
This example shows how to use quoting and escaping.
# This is the default section.
HOME = /temp
configdir = $ENV::HOME/config
[ section_one ]
# Quotes permit leading and trailing whitespace
any = " any variable name "
other = A string that can \
cover several lines \
by including \\ characters
message = Hello World\n
[ section_two ]
greeting = $section_one::message
This example shows how to expand environment variables safely. In this
example, the variable tempfile is intended to refer to a temporary file,
and the environment variable TEMP or TMP, if present, specify the
directory where the file should be put. Since the default section is
checked if a variable does not exist, it is possible to set TMP to
default to /tmp, and TEMP to default to TMP.
# These two lines must be in the default section.
TMP = /tmp
TEMP = $ENV::TMP
# This can be used anywhere
tmpfile = ${ENV::TEMP}/tmp.filename
This example shows how to enforce FIPS mode for the application sample.
sample = fips_config
[fips_config]
alg_section = evp_properties
[evp_properties]
default_properties = "fips=yes"
ENVIRONMENT
OPENSSL_CONF
The path to the config file, or the empty string for none. Ignored
in set-user-ID and set-group-ID programs.
OPENSSL_ENGINES
The path to the engines directory. Ignored in set-user-ID and set-
group-ID programs.
OPENSSL_MODULES
The path to the directory with OpenSSL modules, such as providers.
Ignored in set-user-ID and set-group-ID programs.
OPENSSL_CONF_INCLUDE
The optional path to prepend to all .include paths.
BUGS
There is no way to include characters using the octal \nnn form. Strings
are all null terminated so nulls cannot form part of the value.
The escaping isn't quite right: if you want to use sequences like \n you
can't use any quote escaping on the same line.
The limit that only one directory can be opened and read at a time can
be considered a bug and should be fixed.
HISTORY
An undocumented API, NCONF_WIN32(), used a slightly different set of
parsing rules there were intended to be tailored to the Microsoft
Windows platform. Specifically, the backslash character was not an
escape character and could be used in pathnames, only the double-quote
character was recognized, and comments began with a semi-colon. This
function was deprecated in OpenSSL 3.0; applications with configuration
files using that syntax will have to be modified.
SEE ALSO
openssl-x509(1), openssl-req(1), openssl-ca(1), openssl-fipsinstall(1),
ASN1_generate_nconf(3), EVP_set_default_properties(3),
CONF_modules_load(3), CONF_modules_load_file(3), RAND_bytes(3),
fips_config(5), and x509v3_config(5).
COPYRIGHT
Copyright 2000-2025 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
3.5.4 2025-09-30 CONFIG(5SSL)
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