OPENSSL-PKCS8(1SSL) OpenSSL OPENSSL-PKCS8(1SSL)
NAME
openssl-pkcs8 - PKCS#8 format private key conversion command
SYNOPSIS
openssl pkcs8 [-help] [-topk8] [-inform DER|PEM] [-outform DER|PEM] [-in
filename] [-passin arg] [-out filename] [-passout arg] [-iter count]
[-noiter] [-nocrypt] [-traditional] [-v2 alg] [-v2prf alg] [-v1 alg]
[-scrypt] [-scrypt_N N] [-scrypt_r r] [-scrypt_p p] [-saltlen size]
[-rand files] [-writerand file] [-engine id] [-provider name]
[-provider-path path] [-provparam [name:]key=value] [-propquery propq]
DESCRIPTION
This command processes private keys in PKCS#8 format. It can handle both
unencrypted PKCS#8 PrivateKeyInfo format and EncryptedPrivateKeyInfo
format with a variety of PKCS#5 (v1.5 and v2.0) and PKCS#12 algorithms.
OPTIONS
-help
Print out a usage message.
-topk8
Normally a PKCS#8 private key is expected on input and a private key
will be written to the output file. With the -topk8 option the
situation is reversed: it reads a private key and writes a PKCS#8
format key.
-inform DER|PEM, -outform DER|PEM
The input and formats; the default is PEM. See
openssl-format-options(1) for details.
If a key is being converted from PKCS#8 form (i.e. the -topk8 option
is not used) then the input file must be in PKCS#8 format. An
encrypted key is expected unless -nocrypt is included.
If -topk8 is not used and PEM mode is set the output file will be an
unencrypted private key in PKCS#8 format. If the -traditional option
is used then a traditional format private key is written instead.
If -topk8 is not used and DER mode is set the output file will be an
unencrypted private key in traditional DER format.
If -topk8 is used then any supported private key can be used for the
input file in a format specified by -inform. The output file will be
encrypted PKCS#8 format using the specified encryption parameters
unless -nocrypt is included.
-traditional
When this option is present and -topk8 is not a traditional format
private key is written.
-in filename
This specifies the input file to read a key from or standard input
if this option is not specified. If the key is encrypted a pass
phrase will be prompted for unless -passin is given.
-passin arg, -passout arg
The password source for the input and output file. For more
information about the format of arg see
openssl-passphrase-options(1).
-out filename
This specifies the output file to write a key to or standard output
by default. The output filename can be the same as the input
filename, which leads to replacing the file contents. Note that
file I/O is not atomic. The output file is truncated and then
written.
If any encryption options are set and -passout is not given then a
pass phrase will be prompted for. When password input is
interrupted, the output file is not touched.
-iter count
When creating new PKCS#8 containers, use a given number of
iterations on the password in deriving the encryption key for the
PKCS#8 output. High values increase the time required to brute-
force a PKCS#8 container.
-noiter
When creating new PKCS#8 containers, use 1 as iteration count.
-nocrypt
PKCS#8 keys generated or input are normally PKCS#8
EncryptedPrivateKeyInfo structures using an appropriate password
based encryption algorithm. With this option an unencrypted
PrivateKeyInfo structure is expected or output. This option does
not encrypt private keys at all and should only be used when
absolutely necessary. Certain software such as some versions of Java
code signing software used unencrypted private keys.
-v2 alg
This option sets the PKCS#5 v2.0 algorithm.
The alg argument is the encryption algorithm to use, valid values
include aes128, aes256 and des3. If this option isn't specified then
aes256 is used.
-v2prf alg
This option sets the PRF algorithm to use with PKCS#5 v2.0. A
typical value value would be hmacWithSHA256. If this option isn't
set then the default for the cipher is used or hmacWithSHA256 if
there is no default.
Some implementations may not support custom PRF algorithms and may
require the hmacWithSHA1 option to work.
-v1 alg
This option indicates a PKCS#5 v1.5 or PKCS#12 algorithm should be
used. Some older implementations may not support PKCS#5 v2.0 and
may require this option. If not specified PKCS#5 v2.0 form is used.
-scrypt
Uses the scrypt algorithm for private key encryption using default
parameters: currently N=16384, r=8 and p=1 and AES in CBC mode with
a 256 bit key. These parameters can be modified using the -scrypt_N,
-scrypt_r, -scrypt_p and -v2 options.
-scrypt_N N, -scrypt_r r, -scrypt_p p
Sets the scrypt N, r or p parameters.
-saltlen
Sets the length (in bytes) of the salt to use for the PBE algorithm.
If this value is not specified, the default for PBES2 is 16 (128
bits) and 8 (64 bits) for PBES1.
-rand files, -writerand file
See "Random State Options" in openssl(1) for details.
-engine id
See "Engine Options" in openssl(1). This option is deprecated.
-provider name
-provider-path path
-provparam [name:]key=value
-propquery propq
See "Provider Options" in openssl(1), provider(7), and property(7).
NOTES
By default, when converting a key to PKCS#8 format, PKCS#5 v2.0 using
256 bit AES with HMAC and SHA256 is used.
Some older implementations do not support PKCS#5 v2.0 format and require
the older PKCS#5 v1.5 form instead, possibly also requiring insecure
weak encryption algorithms such as 56 bit DES.
Private keys encrypted using PKCS#5 v2.0 algorithms and high iteration
counts are more secure that those encrypted using the traditional SSLeay
compatible formats. So if additional security is considered important
the keys should be converted.
It is possible to write out DER encoded encrypted private keys in PKCS#8
format because the encryption details are included at an ASN1 level
whereas the traditional format includes them at a PEM level.
PKCS#5 V1.5 AND PKCS#12 ALGORITHMS
Various algorithms can be used with the -v1 command line option,
including PKCS#5 v1.5 and PKCS#12. These are described in more detail
below.
PBE-MD2-DES PBE-MD5-DES
These algorithms were included in the original PKCS#5 v1.5
specification. They only offer 56 bits of protection since they
both use DES.
PBE-SHA1-RC2-64, PBE-MD2-RC2-64, PBE-MD5-RC2-64, PBE-SHA1-DES
These algorithms are not mentioned in the original PKCS#5 v1.5
specification but they use the same key derivation algorithm and are
supported by some software. They are mentioned in PKCS#5 v2.0. They
use either 64 bit RC2 or 56 bit DES.
PBE-SHA1-RC4-128, PBE-SHA1-RC4-40, PBE-SHA1-3DES, PBE-SHA1-2DES,
PBE-SHA1-RC2-128, PBE-SHA1-RC2-40
These algorithms use the PKCS#12 password based encryption algorithm
and allow strong encryption algorithms like triple DES or 128 bit
RC2 to be used.
EXAMPLES
Convert a private key to PKCS#8 format using default parameters (AES
with 256 bit key and hmacWithSHA256):
openssl pkcs8 -in key.pem -topk8 -out enckey.pem
Convert a private key to PKCS#8 unencrypted format:
openssl pkcs8 -in key.pem -topk8 -nocrypt -out enckey.pem
Convert a private key to PKCS#5 v2.0 format using triple DES:
openssl pkcs8 -in key.pem -topk8 -v2 des3 -out enckey.pem
Convert a private key to PKCS#5 v2.0 format using AES with 256 bits in
CBC mode and hmacWithSHA512 PRF:
openssl pkcs8 -in key.pem -topk8 -v2 aes-256-cbc -v2prf hmacWithSHA512 -out enckey.pem
Convert a private key to PKCS#8 using a PKCS#5 1.5 compatible algorithm
(DES):
openssl pkcs8 -in key.pem -topk8 -v1 PBE-MD5-DES -out enckey.pem
Convert a private key to PKCS#8 using a PKCS#12 compatible algorithm
(3DES):
openssl pkcs8 -in key.pem -topk8 -out enckey.pem -v1 PBE-SHA1-3DES
Read a DER unencrypted PKCS#8 format private key:
openssl pkcs8 -inform DER -nocrypt -in key.der -out key.pem
Convert a private key from any PKCS#8 encrypted format to traditional
format:
openssl pkcs8 -in pk8.pem -traditional -out key.pem
Convert a private key to PKCS#8 format, encrypting with AES-256 and with
one million iterations of the password:
openssl pkcs8 -in key.pem -topk8 -v2 aes-256-cbc -iter 1000000 -out pk8.pem
STANDARDS
Test vectors from this PKCS#5 v2.0 implementation were posted to the
pkcs-tng mailing list using triple DES, DES and RC2 with high iteration
counts, several people confirmed that they could decrypt the private
keys produced and therefore, it can be assumed that the PKCS#5 v2.0
implementation is reasonably accurate at least as far as these
algorithms are concerned.
The format of PKCS#8 DSA (and other) private keys is not well
documented: it is hidden away in PKCS#11 v2.01, section 11.9. OpenSSL's
default DSA PKCS#8 private key format complies with this standard.
BUGS
There should be an option that prints out the encryption algorithm in
use and other details such as the iteration count.
SEE ALSO
openssl(1), openssl-dsa(1), openssl-rsa(1), openssl-genrsa(1),
openssl-gendsa(1)
HISTORY
The -iter option was added in OpenSSL 1.1.0.
The -engine option was deprecated in OpenSSL 3.0.
COPYRIGHT
Copyright 2000-2023 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 OPENSSL-PKCS8(1SSL)
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