hash_pbkdf2

(PHP 5 >= 5.5.0, PHP 7)

hash_pbkdf2 — Generate a PBKDF2 key derivation of a supplied password

Descrierea

hash_pbkdf2 ( string $algo , string $password , string $salt , int $iterations , int $length = 0 , bool $binary = false ) : string

Parametri

algo

Name of selected hashing algorithm (i.e. md5, sha256, haval160,4, etc..) See hash_algos() for a list of supported algorithms.

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.

Valorile întoarse

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.

Erori/Excepții

An E_WARNING will be raised 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).

Istoricul schimbărilor

Versiune	Descriere
7.2.0	Usage of non-cryptographic hash functions (adler32, crc32, crc32b, fnv132, fnv1a32, fnv164, fnv1a64, joaat) was disabled.

Exemple

Example #1 hash_pbkdf2() example, basic usage


<?php
$password = "password";
$iterations = 1000;

// Generate a random IV using openssl_random_pseudo_bytes()
// random_bytes() or another suitable source of randomness
$salt = openssl_random_pseudo_bytes(16);

$hash = hash_pbkdf2("sha256", $password, $salt, $iterations, 20);
echo $hash;
?>

Exemplul de mai sus va afișa ceva similar cu:

120fb6cffcf8b32c43e7

Note

Precauţie

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.

A se vedea și

crypt() - One-way string hashing
password_hash() - Creates a password hash
hash() - Generate a hash value (message digest)
hash_algos() - Return a list of registered hashing algorithms
hash_init() - Initialize an incremental hashing context
hash_hmac() - Generate a keyed hash value using the HMAC method
hash_hmac_file() - Generate a keyed hash value using the HMAC method and the contents of a given file
openssl_pbkdf2() - Generates a PKCS5 v2 PBKDF2 string

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User Contributed Notes 13 notes

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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.

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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));
    }
}

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Trevor Herselman ¶

8 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;
    }
}

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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)

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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 ) );

?>

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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
        );
    }
}

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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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Yahe ¶

5 years ago


On an error hash_pbkdf2() will not just raise an E_WARNING but it will also return FALSE.

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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

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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);

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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;
        }
    }
}

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-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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-7

Peter ¶

10 years ago


See also https://github.com/rchouinard/hash_pbkdf2-compat for a compatibility function

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