ConFoo 2025

    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.

    See Also

    Found A Problem?

    Learn How To Improve This Page • Submit a Pull Request • Report a Bug
    ＋add a note

    User Contributed Notes 12 notes

    up
    26
    clarence.pchy(at)gmail.com
    8 years ago
    Please pay great attention to the **$length** parameter! It is exactly the **return string length**, NOT the length of raw binary hash result.

    I had a big problem about this --
    I thought that `hash_pbkdf2(...false)` should equals to `bin2hex(hash_pbkdf2(...true))` just like `md5($x)` equals `bin2hex(md5($x, true))`. However I was wrong:

    hash_pbkdf2('sha256', '123456', 'abc', 10000, 50, false); // returns string(50) "584bc5b41005169f1fa15177edb78d75f9846afc466a4bae05"
    hash_pbkdf2('sha256', '123456', 'abc', 10000, 50, true); // returns string(50) "XKŴ��Qw�u��j�FjK���BFW�YpG �mp.g2�`;N�"
    bin2hex(hash_pbkdf2('sha256', '123456', 'abc', 10000, 50, true)); // returns string(100) "584bc5b41005169f1fa15177edb78d75f9846afc466a4bae05119c82424657c81b5970471f098a6d702e6732b7603b194efe"

    So I add such a note. Hope it will help someone else like me.
    up
    7
    does dot not at matter dot org
    11 years ago
    this snippet was posted over a year ago on a dutch PHP community: (reference/source: http://www.phphulp.nl/php/script/beveiliging/pbkdf2-een-veilige-manier-om-wachtwoorden-op-te-slaan/1956/pbkdf2php/1757/)

    <?php

    /**
    * @author Chris Horeweg
    * @package Security_Tools
    */

    function pbkdf2($password, $salt, $algorithm = 'sha512', $count = 20000, $key_length = 128, $raw_output = false)
    {
    if(!    in_array($algorithm, hash_algos(), true)) {
    exit(    'pbkdf2: Hash algoritme is niet geinstalleerd op het systeem.');
    }

    if(    $count <= 0 || $key_length <= 0) {
    $count = 20000;
    $key_length = 128;
    }

    $hash_length = strlen(hash($algorithm, "", true));
    $block_count = ceil($key_length / $hash_length);

    $output = "";
    for(    $i = 1; $i <= $block_count; $i++) {
    $last = $salt . pack("N", $i);
    $last = $xorsum = hash_hmac($algorithm, $last, $password, true);
    for (    $j = 1; $j < $count; $j++) {
    $xorsum ^= ($last = hash_hmac($algorithm, $last, $password, true));
    }
    $output .= $xorsum;
    }

    if(    $raw_output) {
    return     substr($output, 0, $key_length);
    }
    else {
    return     base64_encode(substr($output, 0, $key_length));
    }
    }
    up
    8
    Trevor Herselman
    9 years ago
    This is a light-weight drop-in replacement for PHP's hash_pbkdf2(); written for compatibility with older versions of PHP.
    Written, formatted and tested by myself, but using code and ideas based on the following:
    https://defuse.ca/php-pbkdf2.htm
    https://github.com/rchouinard/hash_pbkdf2-compat/blob/master/src/hash_pbkdf2.php
    https://gist.github.com/rsky/5104756

    My main goals:
    1) Maximum compatibility with PHP hash_pbkdf2(), ie. a drop-in replacement function
    2) Minimum code size/bloat
    3) Easy to copy/paste
    4) No classes, and not encapsulated in a class! Why write a class when a simple function will do?
    5) Eliminate calls to sprintf(). (used by other examples for the error reporting)
    6) No other dependencies, ie. extra required functions

    <?php
    if (!function_exists('hash_pbkdf2'))
    {
    function     hash_pbkdf2($algo, $password, $salt, $count, $length = 0, $raw_output = false)
    {
    if (!    in_array(strtolower($algo), hash_algos())) trigger_error(__FUNCTION__ . '(): Unknown hashing algorithm: ' . $algo, E_USER_WARNING);
    if (!    is_numeric($count)) trigger_error(__FUNCTION__ . '(): expects parameter 4 to be long, ' . gettype($count) . ' given', E_USER_WARNING);
    if (!    is_numeric($length)) trigger_error(__FUNCTION__ . '(): expects parameter 5 to be long, ' . gettype($length) . ' given', E_USER_WARNING);
    if (    $count <= 0) trigger_error(__FUNCTION__ . '(): Iterations must be a positive integer: ' . $count, E_USER_WARNING);
    if (    $length < 0) trigger_error(__FUNCTION__ . '(): Length must be greater than or equal to 0: ' . $length, E_USER_WARNING);

    $output = '';
    $block_count = $length ? ceil($length / strlen(hash($algo, '', $raw_output))) : 1;
    for (    $i = 1; $i <= $block_count; $i++)
    {
    $last = $xorsum = hash_hmac($algo, $salt . pack('N', $i), $password, true);
    for (    $j = 1; $j < $count; $j++)
    {
    $xorsum ^= ($last = hash_hmac($algo, $last, $password, true));
    }
    $output .= $xorsum;
    }

    if (!    $raw_output) $output = bin2hex($output);
    return     $length ? substr($output, 0, $length) : $output;
    }
    }
    up
    7
    Anonymous
    11 years ago
    Sadly this function was added in PHP 5.5 but many webservers just provide PHP 5.3. But there exists a pure PHP implementation (found here: https://defuse.ca/php-pbkdf2.htm).
    I took this implementation, put it into a class with comments for PHPDoc and added a switch so that the native PHP function is used if available.

    Feel free to use it!
    http://pastebin.com/f5PDq735
    (Posted on pastebin.com since the text would have been too long)
    up
    2
    php . ober-mail . de
    3 years ago
    If you are wondering what the requirements are for the salt, have a look at the RFC[1]:

    "The salt parameter should be a random string containing at least 64 bits of entropy. That means when generated from a function like *mcrypt_create_iv*, at least 8 bytes long. But for salts that consist of only *a-zA-Z0-9* (or are base_64 encoded), the minimum length should be at least 11 characters. It should be generated random for each password that's hashed, and stored along side the generated key."

    [1] https://wiki.php.net/rfc/hash_pbkdf2
    up
    1
    Yahe
    5 years ago
    On an error hash_pbkdf2() will not just raise an E_WARNING but it will also return FALSE.
    up
    1
    nimasdj [AT] yahoo [DOT] com
    8 years ago
    There is a mistake in the class provided by Binod Kumar Luitel (http://php.net/manual/en/function.hash-pbkdf2.php#113488):
    this line:
    return bin2hex(substr($this->output, 0, $this->key_length));
    must be changed to:
    return substr(bin2hex($this->output), 0, $this->key_length);
    up
    1
    Flimm
    6 years ago
    Note that if $raw_output is false, then the output will be encoded using lowercase hexits. Some other systems (such as Django 2.0) use base64 instead. So if you're trying to generate hash strings that are compatible with those systems, you can use the base64_encode function, like this:

    <?php

    echo base64_encode( hash_pbkdf2( "sha256", "example password", "BbirbJq1C1G7", 100000, 0, true ) );

    ?>
    up
    1
    gfilippakis at sleed dot gr
    5 years ago
    This is a very basic implementation of Rfc2898DeriveBytes class with only 2 of its constructors in case someone else finds it useful.

    class Rfc2898DeriveBytes
    {
    private $textToHash;
    private $saltByteSize;

    public $salt;

    public function __construct($arg1, $arg2)
    {
    if (is_string($arg1) && is_integer($arg2)) {
    $this->textToHash = $arg1;
    $this->saltByteSize = $arg2;
    $this->salt = substr(
    hex2bin(sha1(uniqid('', true))),
    0,
    $this->saltByteSize
    );
    } elseif (is_string($arg1) && is_string($arg2)) {
    $this->textToHash = $arg1;
    $this->salt = $arg2;
    }
    }

    public function getBytes($size)
    {
    return hash_pbkdf2(
    "sha1",
    $this->textToHash,
    $this->salt,
    1000,
    $size,
    true
    );
    }
    }
    up
    -1
    Binod Kumar Luitel
    11 years ago
    People who wants pure PHP implementation of the function, i.e. who don't have PHP 5.5 installed within their server, can use the following implementation. Nothing has been modified so far as from reference https://defuse.ca/php-pbkdf2.htm but the OOP lovers might like this.
    For more information about PBKDF2 see: http://en.wikipedia.org/wiki/PBKDF2

    <?php
    /**
    * PBKDF2 key derivation function as defined by RSA's PKCS #5: https://www.ietf.org/rfc/rfc2898.txt
    * $algorithm - The hash algorithm to use. Recommended: SHA256
    * $password - The password.
    * $salt - A salt that is unique to the password.
    * $count - Iteration count. Higher is better, but slower. Recommended: At least 1000.
    * $key_length - The length of the derived key in bytes.
    * $raw_output - If true, the key is returned in raw binary format. Hex encoded otherwise.
    * Returns: A $key_length-byte key derived from the password and salt.
    */
    if (!function_exists("hash_pbkdf2")) {
    function     hash_pbkdf2($algorithm, $password, $salt, $count, $key_length, $raw_output = false) {

    class     pbkdf2 {
    public     $algorithm;
    public     $password;
    public     $salt;
    public     $count;
    public     $key_length;
    public     $raw_output;

    private     $hash_length;
    private     $output = "";

    public function     __construct($data = null)
    {
    if (    $data != null) {
    $this->init($data);
    }
    }

    public function     init($data)
    {
    $this->algorithm = $data["algorithm"];
    $this->password = $data["password"];
    $this->salt = $data["salt"];
    $this->count = $data["count"];
    $this->key_length = $data["key_length"];
    $this->raw_output = $data["raw_output"];
    }

    public function     hash()
    {
    $this->algorithm = strtolower($this->algorithm);
    if(!    in_array($this->algorithm, hash_algos(), true))
    throw new     Exception('PBKDF2 ERROR: Invalid hash algorithm.');

    if(    $this->count <= 0 || $this->key_length <= 0)
    throw new     Exception('PBKDF2 ERROR: Invalid parameters.');

    $this->hash_length = strlen(hash($this->algorithm, "", true));
    $block_count = ceil($this->key_length / $this->hash_length);
    for (    $i = 1; $i <= $block_count; $i++) {
    // $i encoded as 4 bytes, big endian.
    $last = $this->salt . pack("N", $i);
    // first iteration
    $last = $xorsum = hash_hmac($this->algorithm, $last, $this->password, true);
    // perform the other $this->count - 1 iterations
    for ($j = 1; $j < $this->count; $j++) {
    $xorsum ^= ($last = hash_hmac($this->algorithm, $last, $this->password, true));
    }
    $this->output .= $xorsum;
    if(    $this->raw_output)
    return     substr($this->output, 0, $this->key_length);
    else
    return     bin2hex(substr($this->output, 0, $this->key_length));
    }
    }
    }

    $data = array('algorithm' => $algorithm, 'password' => $password, 'salt' => $salt, 'count' => $count, 'key_length' => $key_length, 'raw_output' => $raw_output);
    try {
    $pbkdf2 = new pbkdf2($data);
    return     $pbkdf2->hash();
    } catch (    Exception $e) {
    throw     $e;
    }
    }
    }
    up
    -2
    php at ober-mail dot de
    3 years ago
    If you are wondering what the requirements are for the salt, have a look at the RFC[1]:

    "The salt parameter should be a random string containing at least 64 bits of entropy. That means when generated from a function like *mcrypt_create_iv*, at least 8 bytes long. But for salts that consist of only *a-zA-Z0-9* (or are base_64 encoded), the minimum length should be at least 11 characters. It should be generated random for each password that's hashed, and stored along side the generated key."

    [1] https://wiki.php.net/rfc/hash_pbkdf2
    up
    -3
    php - ober-mail - de
    3 years ago
    If you are wondering what the requirements are for the salt, have a look at the RFC[1]:

    "The salt parameter should be a random string containing at least 64 bits of entropy. That means when generated from a function like *mcrypt_create_iv*, at least 8 bytes long. But for salts that consist of only *a-zA-Z0-9* (or are base_64 encoded), the minimum length should be at least 11 characters. It should be generated random for each password that's hashed, and stored along side the generated key."

    [1] https://wiki.php.net/rfc/hash_pbkdf2
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