---
name: "libressl-PKCS5_PBKDF2_HMAC"
section: "3"
platform: "linux"
package: "libressl"
version: "4.4.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/libressl-PKCS5_PBKDF2_HMAC"
---

# libressl-PKCS5\_PBKDF2\_HMAC(3)

password based derivation routines with salt and iteration count

## NAME

**PKCS5\_PBKDF2\_HMAC**, **PKCS5\_PBKDF2\_HMAC\_SHA1** – password based derivation routines with salt and iteration count

## SYNOPSIS

Crypto Library (libcrypto, -lcrypto)

**#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.

*pass* is the password used in the derivation of length *passlen*. *pass* is an optional parameter and can be NULL. If *passlen* is -1, then the function will calculate the length of *pass* using [strlen(3)](/strlen/3.md).

*salt* is 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* 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* less than 1 is treated as a single iteration.

*digest* is 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).

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.

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.

## RETURN VALUES

**PKCS5\_PBKDF2\_HMAC**() and **PBKCS5\_PBKDF2\_HMAC\_SHA1**() return 1 on success or 0 on error.

## 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.