PKCS5_PBKDF2_HMAC(3ossl)

📦
version 3.5.9 · 8 versions
, in fedora 43, fedora 44

💖 PKCS5_PBKDF2_HMAC(3ossl) 💖

okay bestie, welcome to the OpenSSL corner of the manual, where we turn your lil password into a big strong key 🔑✨. This is PKCS5_PBKDF2_HMAC, and its ride-or-die PKCS5_PBKDF2_HMAC_SHA1 — the password based derivation routines with salt and iteration count. No cap, they're iconic.

✨ NAME ✨

PKCS5_PBKDF2_HMAC, PKCS5_PBKDF2_HMAC_SHA1 — password based derivation routines with salt and iteration count 🧂🔁

🎀 SYNOPSIS 🎀

#include <openssl/evp.h>

int PKCS5_PBKDF2_HMAC(const char *pass, int passlen,
                      const unsigned char *salt, int saltlen, int iter,
                      const EVP_MD *digest,
                      int keylen, unsigned char *out);

int PKCS5_PBKDF2_HMAC_SHA1(const char *pass, int passlen,
                           const unsigned char *salt, int saltlen, int iter,
                           int keylen, unsigned char *out);

🦋 DESCRIPTION 🦋

So PKCS5_PBKDF2_HMAC() derives a key from a password using a salt and iteration count, exactly as specified in RFC 2898. It's giving "stretch that password until it's a whole key" energy 💅.

  • pass — this is the password used in the derivation, and its length is passlen. It's an optional parameter, so it can be NULL. And if passlen is -1, the function will calculate the length of pass using strlen(). Cute, right?
  • salt — the salt used in the derivation, length saltlen. If the salt is NULL, then saltlen must be 0. Heads up though: the function will not attempt to calculate the length of the salt, because it is not assumed to be NULL terminated. So don't be out here expecting it to guess 🙈.
  • iter — the iteration count, and its value should be greater than or equal to 1. RFC 2898 suggests an iteration count of at least 1000. Any iter value less than 1 is invalid; such values will result in failure and raise the PROV_R_INVALID_ITERATION_COUNT error. So like... don't. 😭
  • digest — the message digest function used in the derivation. And PKCS5_PBKDF2_HMAC_SHA1() just calls PKCS5_PBKDF2_HMAC() with EVP_sha1(). Convenience queen 👑.
  • out — the derived key gets written here, and the size of the out buffer is specified via keylen. So make sure it's big enough, bestie, or it's gonna be a bad time.

🌸 NOTES 🌸

A typical application of this function is to derive keying material for an encryption algorithm from a password in pass, a salt in salt, and an iteration count. That's the whole vibe 🫶.

Increasing the iter parameter slows down the algorithm, which makes it harder for an attacker to perform a brute force attack using a large number of candidate passwords. Slow = safe, periodt 🔥.

These functions make no assumption regarding the given password. It will simply be treated as a byte sequence. No judgement, no drama, just bytes 💜.

⭐ RETURN VALUES ⭐

PKCS5_PBKDF2_HMAC() and PBKCS5_PBKDF2_HMAC_SHA1() return 1 on success or 0 on error. That's it, that's the whole story — 1 slay, 0 not slay.

🌈 SEE ALSO 🌈

Copyright 2014-2021 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>.

and that's the tea, bestie — this page is from OpenSSL 3.5.9, dated 2026-09-29, and it's for PKCS5_PBKDF2_HMAC(3ossl). go forth and derive responsibly 💖✨🎀
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