PKCS8(1SSL) OpenSSL PKCS8(1SSL)
openssl-pkcs8, pkcs8 - PKCS#8 format private key conversion tool
openssl pkcs8 [-help] [-topk8] [-inform PEM|DER] [-outform PEM|DER]
[-in filename] [-passin arg] [-out filename] [-passout arg] [-iter
count] [-noiter] [-nocrypt] [-traditional] [-v2 alg] [-v2prf alg] [-v1
alg] [-engine id] [-scrypt] [-scrypt_N N] [-scrypt_r r] [-scrypt_p p]
The pkcs8 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.
Print out a usage message.
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
This specifies the input format: see "KEY FORMATS" for more
This specifies the output format: see "KEY FORMATS" for more
When this option is present and -topk8 is not a traditional format
private key is written.
This specifies the input filename 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.
the input file password source. For more information about the
format of arg see the PASS PHRASE ARGUMENTS section in openssl(1).
This specifies the output filename to write a key to or standard
output by default. If any encryption options are set then a pass
phrase will be prompted for. The output filename should not be the
same as the input filename.
the output file password source. For more information about the
format of arg see the PASS PHRASE ARGUMENTS section in openssl(1).
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.
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.
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.
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.
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
specifying an engine (by its unique id string) will cause pkcs8 to
attempt to obtain a functional reference to the specified engine,
thus initialising it if needed. The engine will then be set as the
default for all available algorithms.
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.
Various different formats are used by the pkcs8 utility. These are
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.
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.
The encrypted form of a PEM encode PKCS#8 files uses the following
headers and footers:
-----BEGIN ENCRYPTED PRIVATE KEY-----
-----END ENCRYPTED PRIVATE KEY-----
The unencrypted form uses:
-----BEGIN PRIVATE KEY-----
-----END PRIVATE KEY-----
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
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
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.
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
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
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
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
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.
There should be an option that prints out the encryption algorithm in
use and other details such as the iteration count.
dsa(1), rsa(1), genrsa(1), gendsa(1)
The -iter option was added to OpenSSL 1.1.0.
Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (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
1.1.0g 2017-11-04 PKCS8(1SSL)