hash_hmac

(PHP 5 >= 5.1.2, PHP 7, PHP 8, PECL hash >= 1.1)

hash_hmac — Generate a keyed hash value using the HMAC method

Description

hash_hmac(
    string $algo,
    string $data,
    string $key,
    bool $binary = false
): string

Parameters

algo: Name of selected hashing algorithm (i.e. "md5", "sha256", "haval160,4", etc..) See hash_hmac_algos() for a list of supported algorithms.
data: Message to be hashed.
key: Shared secret key used for generating the HMAC variant of the message digest.
binary: When set to true, outputs raw binary data. false outputs lowercase hexits.

Return Values

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

Errors/Exceptions

Throws a ValueError exception if algo is unknown or is a non-cryptographic hash function.

Changelog

Version	Description
8.0.0	Now throws a ValueError exception if `algo` is unknown or is a non-cryptographic hash function; previously, `false` was returned instead.
7.2.0	Usage of non-cryptographic hash functions (adler32, crc32, crc32b, fnv132, fnv1a32, fnv164, fnv1a64, joaat) was disabled.

Examples

Example #1 hash_hmac() example

<?php
echo hash_hmac('sha256', 'The quick brown fox jumped over the lazy dog.', 'secret');
?>

The above example will output:

9c5c42422b03f0ee32949920649445e417b2c634050833c5165704b825c2a53b

User Contributed Notes 18 notes

down

119

Korbendallas ¶

6 years ago


Very important notice, if you pass array to $data, php will generate a Warning, return a NULL and continue your application. Which I think is critical vulnerability as this function used to check authorisation typically.

Example:
<?php
var_dump(hash_hmac('sha256', [], 'secret'));

WARNING hash_hmac() expects parameter 2 to be string, array given on line number 3
NULL
?>
Of course not documented feature.

down

Michiel Thalen, Thalent ¶

8 years ago


As  Michael  uggests we should take care not to compare the hash using == (or ===). Since PHP version 5.6 we can now use hash_equals().

So the example will be:

<?php
    if (hash_equals($hashed_expected, $hashed_value) ) {
        echo "hashes match!";
    }
?>

down

Michael ¶

11 years ago


Please be careful when comparing hashes. In certain cases, information can be leaked by using a timing attack. It takes advantage of the == operator only comparing until it finds a difference in the two strings. To prevent it, you have two options.



Option 1: hash both hashed strings first - this doesn't stop the timing difference, but it makes the information useless.



<?php

    if (md5($hashed_value) === md5($hashed_expected)) {

        echo "hashes match!";

    }

?>



Option 2: always compare the whole string.



<?php

    if (hash_compare($hashed_value, $hashed_expected)) {

        echo "hashes match!";

    }



    function hash_compare($a, $b) {

        if (!is_string($a) || !is_string($b)) {

            return false;

        }

        

        $len = strlen($a);

        if ($len !== strlen($b)) {

            return false;

        }



        $status = 0;

        for ($i = 0; $i < $len; $i++) {

            $status |= ord($a[$i]) ^ ord($b[$i]);

        }

        return $status === 0;

    }

?>

down

pbuttelli at tutanota dot com ¶

2 years ago


While implementing a TOTP application, please note that hash_hmac() must receive data in binary, not in a hexadecimal string, to generate a valid OTP across platforms.

This problem can be easily fixed by converting a hexadecimal string to its binary form before passing it to hash_hmac().

<?php
$time = hex2bin('0000000003523f77'); // time must be in this "hexadecimal and padded" form
$key = hex2bin('bb57d1...'); // 160-bits = 40-digit hexadecimal (4 bits) = 32-digit base32 (5 bits)

hash_hmac('sha1', $time, $key);
?>

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KC Cloyd ¶

15 years ago


Sometimes a hosting provider doesn't provide access to the Hash extension. Here is a clone of the hash_hmac function you can use in the event you need an HMAC generator and Hash is not available. It's only usable with MD5 and SHA1 encryption algorithms, but its output is identical to the official hash_hmac function (so far at least).

<?php

function custom_hmac($algo, $data, $key, $raw_output = false)
{
    $algo = strtolower($algo);
    $pack = 'H'.strlen($algo('test'));
    $size = 64;
    $opad = str_repeat(chr(0x5C), $size);
    $ipad = str_repeat(chr(0x36), $size);

    if (strlen($key) > $size) {
        $key = str_pad(pack($pack, $algo($key)), $size, chr(0x00));
    } else {
        $key = str_pad($key, $size, chr(0x00));
    }

    for ($i = 0; $i < strlen($key) - 1; $i++) {
        $opad[$i] = $opad[$i] ^ $key[$i];
        $ipad[$i] = $ipad[$i] ^ $key[$i];
    }

    $output = $algo($opad.pack($pack, $algo($ipad.$data)));

    return ($raw_output) ? pack($pack, $output) : $output;
}

?>

Example Use:

<?php

custom_hmac('sha1', 'Hello, world!', 'secret', true);

?>

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pete dot walker at NOSPAM dot me dot com ¶

12 years ago


A function implementing the algorithm outlined in RFC 6238 (http://tools.ietf.org/html/rfc6238)

<?php
/**
 * This function implements the algorithm outlined
 * in RFC 6238 for Time-Based One-Time Passwords
 *
 * @link http://tools.ietf.org/html/rfc6238
 * @param string $key    the string to use for the HMAC key
 * @param mixed  $time   a value that reflects a time (unix
 *                       time in the example)
 * @param int    $digits the desired length of the OTP
 * @param string $crypto the desired HMAC crypto algorithm
 * @return string the generated OTP
 */
function oauth_totp($key, $time, $digits=8, $crypto='sha256')
{
    $digits = intval($digits);
    $result = null;
    
    // Convert counter to binary (64-bit)       
    $data = pack('NNC*', $time >> 32, $time & 0xFFFFFFFF);
    
    // Pad to 8 chars (if necessary)
    if (strlen ($data) < 8) {
        $data = str_pad($data, 8, chr(0), STR_PAD_LEFT);
    }        
    
    // Get the hash
    $hash = hash_hmac($crypto, $data, $key);
    
    // Grab the offset
    $offset = 2 * hexdec(substr($hash, strlen($hash) - 1, 1));
    
    // Grab the portion we're interested in
    $binary = hexdec(substr($hash, $offset, 8)) & 0x7fffffff;
    
    // Modulus
    $result = $binary % pow(10, $digits);
    
    // Pad (if necessary)
    $result = str_pad($result, $digits, "0", STR_PAD_LEFT);
    
    return $result;
}
?>

down

Siann Beck ¶

14 years ago


For signing an Amazon AWS query, base64-encode the binary value:

<?php
  $Sig = base64_encode(hash_hmac('sha256', $Request, $AmazonSecretKey, true));
?>

down

havoc at NOSPAM defuse dot ca ¶

12 years ago


Here is an efficient PBDKF2 implementation:

<?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 1024.
 * $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 $key_length-byte key derived from the password and salt.
 *
 * Test vectors can be found here: https://www.ietf.org/rfc/rfc6070.txt
 *
 * This implementation of PBKDF2 was originally created by defuse.ca
 * With improvements by variations-of-shadow.com
 */
function pbkdf2($algorithm, $password, $salt, $count, $key_length, $raw_output = false)
{
    $algorithm = strtolower($algorithm);
    if(!in_array($algorithm, hash_algos(), true))
        die('PBKDF2 ERROR: Invalid hash algorithm.');
    if($count <= 0 || $key_length <= 0)
        die('PBKDF2 ERROR: Invalid parameters.');

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

    $output = "";
    for($i = 1; $i <= $block_count; $i++) {
        // $i encoded as 4 bytes, big endian.
        $last = $salt . pack("N", $i);
        // first iteration
        $last = $xorsum = hash_hmac($algorithm, $last, $password, true);
        // perform the other $count - 1 iterations
        for ($j = 1; $j < $count; $j++) {
            $xorsum ^= ($last = hash_hmac($algorithm, $last, $password, true));
        }
        $output .= $xorsum;
    }

    if($raw_output)
        return substr($output, 0, $key_length);
    else
        return bin2hex(substr($output, 0, $key_length));
}
?>

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Pawel M. ¶

3 years ago


Function for those, who really need to use crc32 algorithm in PHP>7.1

<?php
    function hash_hmac_crc32(string $key, string $data): string
    {
        $b = 4;
        if (strlen($key) > $b) {
            $key = pack("H*", hash('crc32', $key));
        }
        $key  = str_pad($key, $b, chr(0x00));
        $ipad = str_pad('', $b, chr(0x36));
        $opad = str_pad('', $b, chr(0x5c));
        $k_ipad = $key ^ $ipad;
        $k_opad = $key ^ $opad;
        return hash('crc32', $k_opad . hash('crc32', $k_ipad . $data, true));
    }
?>

down

-1

Peter Terence Roux ¶

13 years ago


The Implementation of the PBKDF2 key derivation function as described in RFC 2898 can be used to not only get the hashed KEY but also a specific IV.



To use, one would use it as follows:-



<?php

  $p = str_hash_pbkdf2($pw, $salt, 10, 32, 'sha1');

  $p = base64_encode($p);



  $iv = str_hash_pbkdf2($pw, $salt, 10, 16, 'sha1', 32);

  $iv = base64_encode($iv);

?>



The function should be:-



<?php

  // PBKDF2 Implementation (described in RFC 2898)

  //

  // @param   string  p   password

  // @param   string  s   salt

  // @param   int     c   iteration count (use 1000 or higher)

  // @param   int     kl  derived key length

  // @param   string  a   hash algorithm

  // @param   int     st  start position of result

  //

  // @return  string  derived key

  function str_hash_pbkdf2($p, $s, $c, $kl, $a = 'sha256', $st=0)

  {

    $kb = $start+$kl;                        // Key blocks to compute

    $dk = '';                                    // Derived key



    // Create key

    for ($block=1; $block<=$kb; $block++)

    {

      // Initial hash for this block

      $ib = $h = hash_hmac($a, $s . pack('N', $block), $p, true);



      // Perform block iterations

      for ($i=1; $i<$c; $i++)

      {

        // XOR each iterate

        $ib ^= ($h = hash_hmac($a, $h, $p, true));

      }



      $dk .= $ib;                                // Append iterated block

    }



    // Return derived key of correct length

    return substr($dk, $start, $kl);

  }

?>

down

-1

josefkoh at hotmail dot com ¶

13 years ago


Simple implementation of hmac sha1

<?php

function hmac_sha1($key, $data)
{
    // Adjust key to exactly 64 bytes
    if (strlen($key) > 64) {
        $key = str_pad(sha1($key, true), 64, chr(0));
    }
    if (strlen($key) < 64) {
        $key = str_pad($key, 64, chr(0));
    }

    // Outter and Inner pad
    $opad = str_repeat(chr(0x5C), 64);
    $ipad = str_repeat(chr(0x36), 64);

    // Xor key with opad & ipad
    for ($i = 0; $i < strlen($key); $i++) {
        $opad[$i] = $opad[$i] ^ $key[$i];
        $ipad[$i] = $ipad[$i] ^ $key[$i];
    }

    return sha1($opad.sha1($ipad.$data, true));
}

down

-4

relevant at celsius dot ee ¶

12 years ago


<?php 
/* Here is a solution for those who used hash_hmac 
   with Tiger algorithm in PHP 5.1 - 5.3
   and want to upgrade to PHP 5.4 (or newer?).
   
   The problem occured because the order of bytes for Tiger
   was changed to big endian since PHP 5.4.0.
   
   The two functions below assert $algo is one of Tiger algorithms, 
   for example tiger160,4.
   */
    
# replaces hash('tiger...
function hash_tiger_rev($algo, $data, $raw_output = false) {
    $len = intval(substr($algo, 5, 3)); # 128, 160 or 192 bits
    $times = substr($algo, 9, 1); # 3 or 4
    $revhash = implode("", array_map("strrev", 
        str_split(hash('tiger192,'.$times, $data, true), 8)));
    if ($len < 192) $revhash = substr($revhash, 0, $len >> 3);
    return $raw_output? $revhash: bin2hex($revhash);
}

# replaces hash_hmac('tiger...
function hash_hmac_tiger_rev($algo, $data, $key, $raw_output = false) {
    if (strlen($key) > 64) $key = hash_tiger_rev($algo, $key);
    $key = str_pad($key, 64, chr(0));
    $o_pad = str_repeat("\\", 64) ^ $key; # "\" = chr(0x5C)
    $i_pad = str_repeat("6", 64) ^ $key; # "6" = chr(0x36)
    return hash_tiger_rev($algo, $o_pad . 
           hash_tiger_rev($algo, $i_pad . $data, true), $raw_output);
}

# always the new version of tiger
function hash_hmac_new($algo, $data, $key, $raw_output = false) {
    if (phpversion() > '5.4' || !preg_match('/^tiger(128|160|192),(3|4)$/', $algo)) 
        return hash_hmac($algo, $data, $key, $raw_output);
    else
        return hash_hmac_tiger_rev($algo, $data, $key, $raw_output);
}

# always the old version of tiger
function hash_hmac_old($algo, $data, $key, $raw_output = false) {
    if (phpversion() < '5.4' || !preg_match('/^tiger(128|160|192),(3|4)$/', $algo)) 
        return hash_hmac($algo, $data, $key, $raw_output);
    else
        return hash_hmac_tiger_rev($algo, $data, $key, $raw_output);
}

# let's test it
$algo = 'tiger160,4'; $pwd = 'foo'; $key = 'bar';
echo hash_hmac($algo, $pwd, $key), "<br>";
echo hash_hmac_tiger_rev($algo, $pwd, $key), "<br>"; 
echo "<br>";
echo hash_hmac_old($algo, $pwd, $key), "<br>";
echo hash_hmac_new($algo, $pwd, $key), "<br>";

/* With PHP 5.4 output would be 
   590546d9f425188da35e5dfa53306ba3953571cc
   bd6664330ed96b9b39ee063241b62e43f546a49d

   bd6664330ed96b9b39ee063241b62e43f546a49d
   590546d9f425188da35e5dfa53306ba3953571cc   
    
   With PHP 5.3 
   bd6664330ed96b9b39ee063241b62e43f546a49d
   590546d9f425188da35e5dfa53306ba3953571cc
   
   bd6664330ed96b9b39ee063241b62e43f546a49d
   590546d9f425188da35e5dfa53306ba3953571cc   
*/

?>

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-6

droidlabour at gmail dot com ¶

8 years ago


For signing an Amazon AWS query, base64-encode the binary value:

<?php
echo base64_encode(hash_hmac("sha1", $Request, $AmazonSecretKey, true));
?>

down

-5

brent at thebrent dot net ¶

15 years ago


The hotp algorithms above work with counter values less than 256, but since the counter can be larger, it's necessary to iterate through all the bytes of the counter:

<?php
function oath_hotp ($key, $counter)
{
    // Counter
    //the counter value can be more than one byte long, so we need to go multiple times
    $cur_counter = array(0,0,0,0,0,0,0,0);
    for($i=7;$i>=0;$i--)
    {
        $cur_counter[$i] = pack ('C*', $counter);
        $counter = $counter >> 8;
    }
    $bin_counter = implode($cur_counter);
    // Pad to 8 chars
    if (strlen ($bin_counter) < 8)
    {
        $bin_counter = str_repeat (chr(0), 8 - strlen ($bin_counter)) . $bin_counter;
    }

    // HMAC
    $hash = hash_hmac ('sha1', $bin_counter, $key);
    return $hash;
}

function oath_truncate($hash, $length = 6)
{
    // Convert to dec
    foreach(str_split($hash,2) as $hex)
    {
        $hmac_result[]=hexdec($hex);
    }

    // Find offset
    $offset = $hmac_result[19] & 0xf;

    // Algorithm from RFC
    return
    (
        (($hmac_result[$offset+0] & 0x7f) << 24 ) |
        (($hmac_result[$offset+1] & 0xff) << 16 ) |
        (($hmac_result[$offset+2] & 0xff) << 8 ) |
        ($hmac_result[$offset+3] & 0xff)
    ) % pow(10,$length);
}
print "<pre>";
print "Compare results with:";
print " http://tools.ietf.org/html/draft-mraihi-oath-hmac-otp-04\n";
print "Count\tHash\t\t\t\t\t\tPin\n";
for($i=0;$i<=1024;$i=$i+128)
{
   print $i."\t".($a=oath_hotp("12345678901234567890",$i));
   print "\t".oath_truncate($a)."\n";
}
?>

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-6

Carlos Averett(caverett*@*corecodec,net) ¶

16 years ago


Generating OATH-compliant OTP (one time passwords) results in PHP:

<?php
$otp = oath_truncate (oath_hotp ($key, $counter), $length);
function oath_hotp ($key, $counter) {
        // Counter
        $bin_counter = pack ('C*', $counter);

        // Pad to 8 chars
        if (strlen ($bin_counter) < 8) {
                $bin_counter = str_repeat (chr(0), 8 - strlen ($bin_counter)) . $bin_counter;
        }

        // HMAC
        $hash = hash_hmac ('sha1', $bin_counter, $key);
        return $hash;
}

function oath_truncate ($hash, $length = 6) {
        // The last byte is used as an offset
        $offset = hexdec (substr ($hash, 38)) & 0xf;

        // Extract the relevant part, and clear the first bit
        $hex_truncated = substr ($hash, $offset * 2, 8);
        $bin_truncated = decbin (hexdec ($hex_truncated));
        $bin_truncated[0] = '0';
        $dec_truncated = bindec ($bin_truncated);

        return substr ($dec_truncated, 0 - $length);
}
?>

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-9

omidbahrami1990 at gmail dot com ¶

7 years ago


This Is The Most Secure Way To Hash Your Data,
It Will Be Almost Impossible To Retrieve Your Data.
--------------------------------------------------------
 --- Create Two Random Keys And Save Them In Your Configuration File ---
<?php
// Create A Random Key
echo base64_encode(openssl_random_pseudo_bytes(64));
?>
--------------------------------------------------------
<?php
// Save The Keys In Your Configuration File
define('FIRSTKEY','TNYazlbZ1Mq3HDMiEFDLrRMZBftFqpU2Ipytgytsc+jmQysE8lmigKtmGK+exB337ZOcAgwPpWmoPHL5niO3jA==');
define('SECONDKEY','z5hh/Kax4+HKZ8exOlvGlrHev/6ZynOEn904yiiIcWo/qLXWSfLkzm4NSJiGXu4uR7xxUowOkO26VqAi2p2DYQ==');
?>
--------------------------------------------------------
<?php
function secured_hash($data)
{        
$first_key = base64_decode(FIRSTKEY);
$second_key = base64_decode(SECONDKEY);    
    
$first_hashed = hash_hmac('sha3-512', $data, $first_key, TRUE);    
$second_hashed = hash_hmac('sha3-512', $first_hashed, $second_key);

return $second_hashed;
}
?>

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-10

martin dot papik at ipsec dot info ¶

12 years ago


Yet another OATH HOTP function. Has a 64 bit counter and is a lot shorter. Enjoy.

<?php

function oath_hotp ($secret, $ctr, $len=6) {
        $binctr = pack ('NNC*', $ctr>>32, $ctr & 0xFFFFFFFF);
        $hash = hash_hmac ("sha1", $binctr, $secret);
// This is where hashing stops and truncation begins
        $ofs = 2*hexdec (substr ($hash, 39, 1));
        $int = hexdec (substr ($hash, $ofs, 8)) & 0x7FFFFFFF;
        $pin = substr ($int, -$len);
        $pin = str_pad ($pin, $len, "0", STR_PAD_LEFT);
        return $pin;
}

?>

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-9

torben dot egmose at gmail dot com ¶

15 years ago


HOTP Algorithm that works according to the RCF http://tools.ietf.org/html/draft-mraihi-oath-hmac-otp-04
The test cases from the RCF document the ASCII string as "123456787901234567890".
But the hex decoded to a string is "12345678901234567890".
Secret="12345678901234567890";
Count:
0 755224
1 287082
<?php
function oath_hotp($key,$counter) {

   // Convert to padded binary string
   $data = pack ('C*', $counter);
   $data = str_pad($data,8,chr(0),STR_PAD_LEFT);

   // HMAC
   return hash_hmac('sha1',$data,$key);
}

function oath_truncate($hash, $length = 6) {

   // Convert to dec
   foreach(str_split($hash,2) as $hex) {
      $hmac_result[]=hexdec($hex);
   }

   // Find offset
   $offset = $hmac_result[19] & 0xf;

   // Algorithm from RFC
   return (
         (($hmac_result[$offset+0] & 0x7f) << 24 ) |
         (($hmac_result[$offset+1] & 0xff) << 16 ) |
         (($hmac_result[$offset+2] & 0xff) << 8 ) |
         ($hmac_result[$offset+3] & 0xff)
         ) % pow(10,$length);
}

print "<pre>";
print "Compare results with:"
print " http://tools.ietf.org/html/draft-mraihi-oath-hmac-otp-04\n";
print "Count\tHash\t\t\t\t\t\tPin\n";
for($i=0;$i<10;$i++)
   print $i."\t".($a=oath_hotp("12345678901234567890",$i))
   print "\t".oath_truncate($a)."\n";

add a note

hash_hmac

Description

Parameters

Return Values

Errors/Exceptions

Changelog

Examples

See Also

User Contributed Notes 18 notes