W3cubDocs

/PHP

hash_pbkdf2

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

hash_pbkdf2 — Generate a PBKDF2 key derivation of a supplied password

Description

hash_pbkdf2(
 string $algo,
 #[\SensitiveParameter] string $password,
 string $salt,
 int $iterations,
 int $length = 0,
 bool $binary = false,
 array $options = []
): string

Parameters

algo

Name of selected hashing algorithm (e.g. "sha256"). For a list of supported algorithms see hash_hmac_algos().

Note:

Non-cryptographic hash functions are not allowed.

password

The password to use for the derivation.

salt

The salt to use for the derivation. This value should be generated randomly.

iterations

The number of internal iterations to perform for the derivation.

length

The length of the output string. If binary is true this corresponds to the byte-length of the derived key, if binary is false this corresponds to twice the byte-length of the derived key (as every byte of the key is returned as two hexits).

If 0 is passed, the entire output of the supplied algorithm is used.

binary

When set to true, outputs raw binary data. false outputs lowercase hexits.

options

An array of options for the various hashing algorithms. Currently, only the "seed" key is supported by the MurmurHash variants.

Return Values

Returns a string containing the derived key as lowercase hexits unless binary is set to true in which case the raw binary representation of the derived key is returned.

Errors/Exceptions

Throws a ValueError exception if the algorithm is unknown, the iterations parameter is less than or equal to 0, the length is less than 0 or the salt is too long (greater than INT_MAX - 4).

Changelog

Version	Description
8.0.0	Now throws a ValueError exception on error. Previously, `false` was returned and an `E_WARNING` message was emitted.
7.2.0	Usage of non-cryptographic hash functions (adler32, crc32, crc32b, fnv132, fnv1a32, fnv164, fnv1a64, joaat) was disabled.

Examples

Example #1 hash_pbkdf2() example, basic usage

<?php
$password = "password";
$iterations = 600000;

// Generate a cryptographically secure random salt using random_bytes()
$salt = random_bytes(16);

$hash = hash_pbkdf2("sha256", $password, $salt, $iterations, 20);
var_dump($hash);

// for raw binary, the $length needs to be halved for equivalent results
$hash = hash_pbkdf2("sha256", $password, $salt, $iterations, 10, true);
var_dump(bin2hex($hash));?>

The above example will output something similar to:

string(20) "120fb6cffcf8b32c43e7"
string(20) "120fb6cffcf8b32c43e7"

Notes

Caution

The PBKDF2 method can be used for hashing passwords for storage. However, it should be noted that password_hash() or crypt() with CRYPT_BLOWFISH are better suited for password storage.