Mcrypt

User Contributed Notes

Kyle T 15-Nov-2017 06:41
This was posted before by another user but has been downvoted. I just wanted to confirm that we suffered massive performance issues related to mcrypt on CentOS (PHP 5.6.32) that are not present in other flavors of Linux.

A sampling of 25,000 encrypts/decrypts takes 4-5x longer when running mcrypt on Centos 7 as compared to Ubuntu. Switching out mcrypt for OpenSSL on Centos will result in a massive increase in performance.

For lower traffic website it can be negligible, but when you start seeing significant traffic/load it will quickly bring down a server.
Daniel Esteve 28-Dec-2016 08:06
The Mcrypt library has been declared DEPRECATED since PHP 7.1, to use in its OpenSSL
simonhf at gmail dot com 24-Jun-2015 08:54
Note that there are severe performance problems with PHP mcrypt on many CentOS versions. Please see this CentOS bug:
http://bugs.centos.org/view.php?id=8954
Anonymous 13-Feb-2012 07:35
These are two simple functions I built for 256-bit encryption/decryption with mcrypt.  I've decided to use MCRYPT_RIJNDAEL_128 because it's AES-compliant, and MCRYPT_MODE_CBC.  (ECB mode is inadequate for many purposes because it does not use an IV.)

This function stores a hash of the data to verify that the data was decrypted successfully, but this could be easily removed if necessary.

<?php
function encrypt($decrypted, $password, $salt='!kQm*fF3pXe1Kbm%9') {
 // Build a 256-bit $key which is a SHA256 hash of $salt and $password.
 $key = hash('SHA256', $salt . $password, true);
 // Build $iv and $iv_base64.  We use a block size of 128 bits (AES compliant) and CBC mode.  (Note: ECB mode is inadequate as IV is not used.)
 srand(); $iv = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC), MCRYPT_RAND);
 if (strlen($iv_base64 = rtrim(base64_encode($iv), '=')) != 22) return false;
 // Encrypt $decrypted and an MD5 of $decrypted using $key.  MD5 is fine to use here because it's just to verify successful decryption.
 $encrypted = base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key, $decrypted . md5($decrypted), MCRYPT_MODE_CBC, $iv));
 // We're done!
 return $iv_base64 . $encrypted;
 }

function decrypt($encrypted, $password, $salt='!kQm*fF3pXe1Kbm%9') {
 // Build a 256-bit $key which is a SHA256 hash of $salt and $password.
 $key = hash('SHA256', $salt . $password, true);
 // Retrieve $iv which is the first 22 characters plus ==, base64_decoded.
 $iv = base64_decode(substr($encrypted, 0, 22) . '==');
 // Remove $iv from $encrypted.
 $encrypted = substr($encrypted, 22);
 // Decrypt the data.  rtrim won't corrupt the data because the last 32 characters are the md5 hash; thus any \0 character has to be padding.
 $decrypted = rtrim(mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key, base64_decode($encrypted), MCRYPT_MODE_CBC, $iv), "\0\4");
 // Retrieve $hash which is the last 32 characters of $decrypted.
 $hash = substr($decrypted, -32);
 // Remove the last 32 characters from $decrypted.
 $decrypted = substr($decrypted, 0, -32);
 // Integrity check.  If this fails, either the data is corrupted, or the password/salt was incorrect.
 if (md5($decrypted) != $hash) return false;
 // Yay!
 return $decrypted;
 }
?>
ghoffman at salientdigital dot com 23-Nov-2010 10:23
If you want a quick way to see what ciphers, modes, key, block and iv sizes are supported on your server, try something like the following.

Note: I used this simple bash: `locate libmcrypt` from terminal on Mac OS X to determine the install paths to the algorithms and modes directories. Lots of function calls generate warnings for certain ciphers, hence the use of error suppression.

<?php

$modes = mcrypt_list_modes();
$algorithms = mcrypt_list_algorithms();
foreach($algorithms as $cipher)
{
    echo "<h1 style=\"border-top:1px solid black;\">".$cipher."</h1>\n";
    foreach($modes as $mode)
    {
        echo "<h3>".$mode."</h3>\n";
        @$td = mcrypt_module_open(
            $cipher,
            '/usr/local/libmcrypt-2.5.8/modules/algorithms/',
            $mode,
            '/usr/local/libmcrypt-2.5.8/modules/modes/');
        @$key_size = mcrypt_enc_get_key_size($td);
        @$block_size = mcrypt_get_block_size($cipher,$mode);
        @$iv_size = mcrypt_get_iv_size($cipher, $mode);
        @mcrypt_module_close($td);
        echo "
        <pre> 
            key_size: ". ($key_size?$key_size:'n/a')
      ."    block_size: ". ($block_size?$block_size:'n/a')
      ."    iv_size: ". ($iv_size?$iv_size:'n/a')
      ."  </pre>\n";
        $td=NULL;
        $key_size=NULL;
        $block_size=NULL;
        $iv_size=NULL;
    }
}

?>
Maarten Malaise 11-Apr-2010 02:38
people using phpmyadmin are redirected to this manual if they don't have mcrypt installed. If you want to install mcrypt on debian, first check your php version:

yourserver# php --version

Then install the appropriate version of mcrypt (php5-mcrypt if your php version is 5.x)

yourserver# apt-get install php4-mcrypt
...or...
yourserver# apt-get install php5-mcrypt