openssl_pbkdf2

(PHP 5 >= 5.5.0, PHP 7, PHP 8)

openssl_pbkdf2 — Generates a PKCS5 v2 PBKDF2 string

Description

openssl_pbkdf2(
    #[\SensitiveParameter] string $password,
    string $salt,
    int $key_length,
    int $iterations,
    string $digest_algo = "sha1"
): string|false

openssl_pbkdf2() computes PBKDF2 (Password-Based Key Derivation Function 2), a key derivation function defined in PKCS5 v2.

Parameters

password: Password from which the derived key is generated.
salt: PBKDF2 recommends a crytographic salt of at least 128 bits (16 bytes).
key_length: Length of desired output key.
iterations: The number of iterations desired. » NIST recommends at least 1,000. As of 2023, OWASP recommends 600,000 iterations for PBKDF2-HMAC-SHA256 and 210,000 for PBKDF2-HMAC-SHA512.
digest_algo: Optional hash or digest algorithm from openssl_get_md_methods(). Defaults to SHA-1. It is recommended to set it to SHA-256 or SHA-512.

Return Values

Returns raw binary string or false on failure.

Examples

Example #1 openssl_pbkdf2() example

<?php
$password = 'password';
$salt = openssl_random_pseudo_bytes(16);
$keyLength = 20;
$iterations = 600000;
$generated_key = openssl_pbkdf2($password, $salt, $keyLength, $iterations, 'sha256');
echo bin2hex($generated_key)."\n";
echo base64_encode($generated_key)."\n";
?>

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User Contributed Notes

McGlockenshire

11 years ago

Despite the manual claiming that this is available in PHP 5.5 and above, this function wasn't made available in my local install.

I expect that having a prehistoric OpenSSL library version installed is the likely culprit.

If you're using PHP 5.5 and don't have this function available in your OpenSSL extension, look at the functionally equivalent hash_pbkdf2 function instead.