OPENSSL-KDF(1ossl)

📦 version 3.5.0, in opensuse-leap 16.0

💅 OPENSSL-KDF 💅

okay bestie, so this is the openssl-kdf page from the 1ossl manual section — yes, the OpenSSL one, hi, it's her 👑

✨ NAME ✨

openssl-kdf — perform Key Derivation Function operations 🎀

🌸 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 basically the key derivation functions take a secret or a password and generate a derived key from it. That's the whole vibe. 🔑

👑 OPTIONS 👑

  • -help — prints you a usage message, bestie. that's it. that's the option. 💖
  • -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. if you don't say anything, it goes to standard output by default. 🫶
  • -binary — outputs the derived key in binary form. if you don't specify this, it uses hexadecimal text format instead. hex is the default, iykyk. ✨
  • -cipher name — specifies the cipher the KDF should use. ⚠️ not all KDFs require a cipher, and it is an error to use this option in those cases. so don't just be throwing it around, okay?
  • -digest name — specifies the digest the KDF should use. ⚠️ again: not all KDFs require a digest, and it is an error to use this option in those cases. and hey, to see the list of supported digests, run openssl list -digest-commands. you're welcome. 💅
  • -mac name — specifies the MAC the KDF should use. ⚠️ and once more: not all KDFs require a MAC, and it is an error to use this option in those cases. three for three, iconic consistency. 🌈
  • -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, and I'm about to list every single one because we don't do half measures here:
    • 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. 🔐
    • hexkey:string — alternative to the key: option where the secret key is specified in hexadecimal form (two hex digits per byte). 🧚
    • pass:string — specifies the password as an alphanumeric string (use this if the password contains printable characters only). the password must be specified for PBKDF2 and scrypt. no password, no key, periodt. 🍓
    • 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 this 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). 🧂✨
    • 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. this specifies the info, fixed info, other info or shared info argument as an alphanumeric string (use this if it contains printable characters only). the length must conform to any restrictions of the KDF algorithm. 🦋
    • 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. twin behavior, different outfit. 👯
    • 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). that's the whole dispatch for these four, bestie, go read those. 📚
  • 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. that's nine of them, count 'em. 🔥

🎀 EXAMPLES 🎀

okay these are literally the best part, let's go. all of these give you a hex-encoded derived key unless you add -binary, just so we're clear. 💖

use TLS1-PRF to 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

use HKDF to 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

use SSKDF with KMAC to 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

use SSKDF with HMAC to 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

use SSKDF with Hash to 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

use SSHKDF to 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

use PBKDF2 to 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

use scrypt to 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, your rules, your available KDFs. 🙈

🌟 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) — go read them, bestie, they're all linked and they all slay. 📖✨

🕰️ HISTORY 🕰️

added in OpenSSL 3.0. she's a 3.0 girly. 👑

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>.

okay that's the whole page, no notes, we ate and left no crumbs 💅🧚‍♀️

and for the little sign-off moment: this whole thing is from OpenSSL version 3.5.0, dated 2026-09-25, and the page lives under the name OPENSSL-KDF(1ossl). slay, bye bestie 🫶💖🌸

📦 where this page comes from