openssl-pkcs8 - PKCS#8 format private key conversion command
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]
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.
- -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).
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.
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
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.
openssl(1), openssl-dsa(1), openssl-rsa(1),
openssl-genrsa(1), openssl-gendsa(1)
The -iter option was added in OpenSSL 1.1.0.
The -engine option was deprecated in OpenSSL 3.0.
Copyright 2000-2026 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>.
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