PKCS5_PBKDF2_HMAC(3)

okay so welcome to the PKCS5_PBKDF2_HMAC(3) page in the Library Functions Manual, bestie — it's a libcrypto situation and we're deriving keys from passwords with salt and iteration count. periodt. 💖

🌸 NAME 🌸

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

✨ SYNOPSIS ✨

library “libcrypto” #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 💅

PKCS5_PBKDF2_HMAC() derives a key from a password using a salt and iteration count as specified in RFC 2898. no cap.

• pass — the password used in the derivation of length passlen. It's an optional parameter and can be NULL. If passlen is -1, then the function will calculate the length of pass using strlen(3).
• salt — the salt used in the derivation of length saltlen. 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 NUL terminated.
• 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 less than 1 is treated as a single iteration.
• digest — the message digest function used in the derivation. Values include any of the EVP_* message digests. PKCS5_PBKDF2_HMAC_SHA1() calls PKCS5_PBKDF2_HMAC() with EVP_sha1(3).
• out — the derived key will be written to out. The size of the out buffer is specified via keylen.

A typical application of this function is to derive keying material for an encryption algorithm from a password in the pass, a salt in salt, and an iteration count. iconic behavior, honestly. 🎀

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. the way that's literally the whole point — highkey obsessed. 🔥

🫶 RETURN VALUES 🫶

PKCS5_PBKDF2_HMAC() and PBKCS5_PBKDF2_HMAC_SHA1() — yes bestie, that's exactly how the page spells it, not me — return 1 on success or 0 on error. copying it verbatim, no cap. 💜

🦋 SEE ALSO 🦋

• EVP_BytesToKey(3)
• EVP_DigestInit(3)

🌈 HISTORY 🌈

• PKCS5_PBKDF2_HMAC_SHA1() first appeared in OpenSSL 0.9.4 and has been available since OpenBSD 2.6.
• PKCS5_PBKDF2_HMAC() first appeared in OpenSSL 1.0.0 and has been available since OpenBSD 4.9.

okay bye bestie, this page is from Debian, dated June 8, 2025, and it's the PKCS5_PBKDF2_HMAC(3) manual — slay. 💅🎀