OPENSSL-PKCS8(1ossl)

📦
version 15.1 · 2 versions
, in freebsd 15.1

💜 NAME 💜

openssl-pkcs8 — the PKCS#8 format private key conversion command, and honestly it's the glow-up station for your keys ✨

🌸 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 🦋

Okay so this command processes private keys in PKCS#8 format, and it's lowkey a multitasker. It handles both the unencrypted PKCS#8 PrivateKeyInfo format and the EncryptedPrivateKeyInfo format, with a whole variety pack of PKCS#5 (v1.5 and v2.0) and PKCS#12 algorithms. It's giving "I contain multitudes" 💅

✨ OPTIONS ✨

  • -help — prints out a usage message. the classic "what do I do" button 🫶
  • -topk8 — okay, normally this command expects a PKCS#8 private key on input and writes a plain private key out. With -topk8 the whole situation is reversed: it reads a private key in and writes a PKCS#8 format key out. flip era 🔄
  • -inform DER|PEM, -outform DER|PEM — the input and formats; default is PEM. peek openssl-format-options(1) for the deets.

If a key is being converted from PKCS#8 form (i.e. -topk8 is not used) then your input file must be in PKCS#8 format, no cap. An encrypted key is expected unless you include -nocrypt.

If -topk8 is not used and PEM mode is set, the output file will be an unencrypted private key in PKCS#8 format. But if -traditional is used, a traditional format private key gets 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 your input file, in whatever format -inform says. The output file will be encrypted PKCS#8 format, using the encryption parameters you specified — unless -nocrypt is in the mix.

  • -traditional — when this option is present and -topk8 is not, a traditional format private key is written. old school, but make it cute 🎀
  • -in filename — specifies the input file to read a key from, or standard input if you don't specify this option. 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 info about the format of arg, see openssl-passphrase-options(1).
  • -out filename — specifies the output file to write a key to, or standard output by default. Fun fact: the output filename can be the same as the input filename, which leads to replacing the file contents. But heads up 👀 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, a pass phrase will be prompted for. When password input is interrupted, the output file is not touched. tiny mercy 🫶

  • -iter count — when creating new PKCS#8 containers, use a given number of iterations on the password when deriving the encryption key for the PKCS#8 output. High values increase the time required to brute-force a PKCS#8 container. more iterations = more pain for the hackers 🔥
  • -noiter — when creating new PKCS#8 containers, use 1 as iteration count. (yes, one. that's the whole bit 💀)
  • -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.
real talk: this option does not encrypt private keys at all and should only be used when absolutely necessary. Certain software — like some versions of Java code signing software — used unencrypted private keys. so like, only if you must, bestie 😭
  • -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. slay.

  • -v2prf alg — this option sets the PRF algorithm to use with PKCS#5 v2.0. A typical 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. (they're a little set in their ways, we forgive them 🙈)

  • -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. glossy AND secure 💅
  • -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. the default is already iconic, honestly 👑

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. 🚩 like, be aware.

Private keys encrypted using PKCS#5 v2.0 algorithms and high iteration counts are more secure than those encrypted using the traditional SSLeay compatible formats. So if additional security is considered important, the keys should be converted. glow-up time 💖

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. nerdy but make it fashion 🧚

🎀 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. Here's the deep dive:

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. only 56 bits. the audacity 💀

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. now that's what we call a serve 🔥

🍓 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. peer reviewed, bestie 🫶

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. it's giving "buried treasure" 🗝️

💀 BUGS 💀

There should be an option that prints out the encryption algorithm in use and other details such as the iteration count. (not yet, bestie. we wait. 😭)

👑 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 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>.

okay that's the whole page, and it's literally all of it, no skips no cuts 💅 this drop is from version 3.5.6, dated 2026-04-07 — mwah, go forth and convert your keys, bestie 🦋✨

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