PKCS5_PBKDF2_HMAC(3SSL)

📦
version 4.0.3 · 14 versions
, in ubuntu stonking

✨ NAME ✨

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

(these are from the OpenSSL 3SSL manual, bestie, ikyk)

📜 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 🌸

Okay 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 "we take your silly little password and turn it into actual key material" energy 👑

Let's do the parameters one by one, no skipping, fr fr:

  • pass is the password used in the derivation, and it's passlen bytes long. It's an optional parameter and can totally be NULL, nbd 🙈. But if passlen is -1, the function will calculate the length of pass using strlen().
  • salt is the salt used in the derivation, and it's saltlen bytes long. If the salt is NULL, then saltlen must be 0. The function will not attempt to calculate the length of the salt, because it is not assumed to be NULL terminated. (she's not gonna guess, periodt 💅)
  • iter is 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. 🚩
Lowkey important: lower bounds checks are provider dependent and are described in the "Supported parameters" in EVP_KDF-PBKDF2(7) — specifically OSSL_KDF_PARAM_PKCS5. So the vibes of what counts as "valid" are not all yours to decide, bestie 😭
  • digest is the message digest function used in the derivation. And PKCS5_PBKDF2_HMAC_SHA1() is literally just calling PKCS5_PBKDF2_HMAC() with EVP_sha1(). One-line queen ✨

The derived key will be written to out. The size of the out buffer is specified via keylen. 🎀

📝 NOTES 📝

A typical application of this function — and by "typical" we mean "the entire point" — 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 arc, that's the story 🦋

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. Like yes it's slower for you too but that's the point, it's a feature not a bug, we love a ✨deliberately expensive✨ moment 🔥

These functions make no assumption regarding the given password. It will simply be treated as a byte sequence. No judgement, no validation, no side-eye. 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 scoring system, iconic and simple 👑

👀 SEE ALSO 👀

Copyright 2014-2026 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>.

okay bestie that's the whole page fr fr 💖 this was version 4.0.3, dated 2026-09-29, from the PKCS5_PBKDF2_HMAC(3SSL) manual — go forth and derive responsibly, mwah 🌈🌸💅

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