OPENSSL-KDF(1ossl)

📦
version 3.5.9 · 8 versions
, in alpine 3.23, alpine 3.24

💅 openssl-kdf — perform Key Derivation Function operations 💅

Okay bestie, listen. This is the openssl-kdf page from the OpenSSL manual (section 1ossl), and it's genuinely so iconic — it's literally the tool that takes your secret-or-password and spins it into a derived key. Let's get into it ✨

✨ SYNOPSIS ✨

openssl kdf [-help] [-cipher] [-digest] [-mac] [-kdfopt nm:v] [-keylen
num] [-out filename] [-binary] [-provider name] [-provider-path path]
[-provparam [name:]key=value] [-propquery propq] kdf_name

🦋 DESCRIPTION 🦋

So like, key derivation functions generate a derived key from either a secret or a password. That's the whole vibe. Secret in, derived key out. 🔥

🎀 OPTIONS 🎀

  • -help — prints a usage message. The classic "wait what do I do" button 🫶
  • -keylen num — the output size of the derived key. This field is required, no cap. You literally cannot skip it. 💀
  • -out filename — the filename to output to. Or, if you don't say anything, it goes to standard output. Default queen behavior 👑
  • -binary — outputs the derived key in binary form. If you don't specify this, it uses hexadecimal text format instead.
  • -cipher name — specifies the cipher to be used by the KDF. But heads up: not all KDFs require a cipher, and it is an error to use this option in those cases. Read the room, bestie 🙈
  • -digest name — specifies the digest to be used by the KDF. Same deal: not all KDFs require a digest, and it is an error to use this option in such cases. Wanna see the list of supported digests? Run openssl list -digest-commands. Slay.
  • -mac name — specifies the MAC to be used by the KDF. And yes, again: not all KDFs require a MAC, and it is an error to use this option in such cases. Pattern recognition is a skill 💅
  • -kdfopt nm:v — passes options to the KDF algorithm. A comprehensive list of parameters lives in "PARAMETERS" in EVP_KDF(3). The common parameter names used by EVP_KDF_CTX_set_params() are:
    • key:string — specifies the secret key as an alphanumeric string (use this if the key contains printable characters only). The string length must conform to any restrictions of the KDF algorithm. A key must be specified for most KDF algorithms. Most. Not all. iykyk.
    • hexkey:string — alternative to the key: option, where the secret key is specified in hexadecimal form (two hex digits per byte). Hex girlies rise 🌸
    • pass:string — specifies the password as an alphanumeric string (use if the password contains printable characters only). The password must be specified for PBKDF2 and scrypt. Non-negotiable, fr fr.
    • hexpass:string — alternative to the pass: option where the password is specified in hexadecimal form (two hex digits per byte).
    • salt:string — specifies a non-secret unique cryptographic salt as an alphanumeric string (use if it contains printable characters only). The length must conform to any restrictions of the KDF algorithm. A salt parameter is required for several KDF algorithms, such as EVP_KDF-PBKDF2(7). Salt is not optional, it's a lifestyle 🧂
    • hexsalt:string — alternative to the salt: option where the salt is specified in hexadecimal form (two hex digits per byte).
    • info:string — some KDF implementations, such as EVP_KDF-HKDF(7), take an 'info' parameter for binding the derived key material to application- and context-specific information. Specifies the info, fixed info, other info or shared info argument as an alphanumeric string (use if it contains printable characters only). The length must conform to any restrictions of the KDF algorithm. So many info names, one parameter 💖
    • hexinfo:string — alternative to the info: option where the info is specified in hexadecimal form (two hex digits per byte).
    • digest:string — this option is identical to the -digest option.
    • cipher:string — this option is identical to the -cipher option.
    • mac:string — this option is identical to the -mac option.
  • -provider name, -provider-path path, -provparam [name:]key=value, -propquery propq — see "Provider Options" in openssl(1), provider(7), and property(7). Provider lore, go read it 📚
  • kdf_name — specifies the name of a supported KDF algorithm which will be used. The supported algorithm names include TLS1-PRF, HKDF, SSKDF, PBKDF2, SSHKDF, X942KDF-ASN1, X942KDF-CONCAT, X963KDF and SCRYPT. Pick your fighter ⭐

🌈 EXAMPLES 🌈

TLS1-PRF — create a hex-encoded derived key from a secret key and seed:

openssl kdf -keylen 16 -kdfopt digest:SHA2-256 -kdfopt key:secret \
            -kdfopt seed:seed TLS1-PRF

HKDF — create a hex-encoded derived key from a secret key, salt and info:

openssl kdf -keylen 10 -kdfopt digest:SHA2-256 -kdfopt key:secret \
            -kdfopt salt:salt -kdfopt info:label HKDF

SSKDF with KMAC — create a hex-encoded derived key from a secret key, salt and info:

openssl kdf -keylen 64 -kdfopt mac:KMAC-128 -kdfopt maclen:20 \
            -kdfopt hexkey:b74a149a161545 -kdfopt hexinfo:348a37a2 \
            -kdfopt hexsalt:3638271ccd68a2 SSKDF

SSKDF with HMAC — create a hex-encoded derived key from a secret key, salt and info:

openssl kdf -keylen 16 -kdfopt mac:HMAC -kdfopt digest:SHA2-256 \
            -kdfopt hexkey:b74a149a -kdfopt hexinfo:348a37a2 \
            -kdfopt hexsalt:3638271c SSKDF

SSKDF with Hash — create a hex-encoded derived key from a secret key, salt and info:

openssl kdf -keylen 14 -kdfopt digest:SHA2-256 \
            -kdfopt hexkey:6dbdc23f045488 \
            -kdfopt hexinfo:a1b2c3d4 SSKDF

SSHKDF — create a hex-encoded derived key from a secret key, hash and session_id:

openssl kdf -keylen 16 -kdfopt digest:SHA2-256 \
            -kdfopt hexkey:0102030405 \
            -kdfopt hexxcghash:06090A \
            -kdfopt hexsession_id:01020304 \
            -kdfopt type:A SSHKDF

PBKDF2 — create a hex-encoded derived key from a password and salt:

openssl kdf -keylen 32 -kdfopt digest:SHA256 -kdfopt pass:password \
            -kdfopt salt:salt -kdfopt iter:2 PBKDF2

scrypt — create a hex-encoded derived key from a password and salt:

openssl kdf -keylen 64 -kdfopt pass:password -kdfopt salt:NaCl \
            -kdfopt n:1024 -kdfopt r:8 -kdfopt p:16 \
            -kdfopt maxmem_bytes:10485760 SCRYPT

💜 NOTES 💜

The KDF mechanisms that are available will depend on the options used when building OpenSSL. So like, your build determines your destiny. Build flags matter, bestie 🛠️

🦋 SEE ALSO 🦋

openssl(1), openssl-pkeyutl(1), EVP_KDF(3), EVP_KDF-SCRYPT(7), EVP_KDF-TLS1_PRF(7), EVP_KDF-PBKDF2(7), EVP_KDF-HKDF(7), EVP_KDF-SS(7), EVP_KDF-SSHKDF(7), EVP_KDF-X942-ASN1(7), EVP_KDF-X942-CONCAT(7), EVP_KDF-X963(7)

⭐ HISTORY ⭐

Added in OpenSSL 3.0. A modern icon, honestly.

Copyright 2019-2023 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>.

Legal said I have to keep this: you may not use this file except in compliance with the License. Do with that what you will 💅

Okay that's the whole page, bestie, we ate and left zero crumbs 🍓 This glorious thing is from OpenSSL 3.5.9, dated 2026-09-29 — go forth and derive some keys, mwah 💖✨🎀

📦 where this page comes from