Manual: openssl-pkcs8
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
.
3.5.5 2026-01-27 OPENSSL-PKCS8(1SSL)