Encrypting Communication between C# and PHP

<?php
/* vim: set expandtab tabstop=4 shiftwidth=4 softtabstop=4: */

/**
 * Random Number Generator
 *
 * PHP versions 4 and 5
 *
 * Here's a short example of how to use this library:
 * <code>
 * <?php
 *    include('Crypt/Random.php');
 *
 *    echo crypt_random();
 * ?>
 * </code>
 *
 * LICENSE: Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 * @category   Crypt
 * @package    Crypt_Random
 * @author     Jim Wigginton <terrafrost@php.net>
 * @copyright  MMVII Jim Wigginton
 * @license    http://www.opensource.org/licenses/mit-license.html  MIT License
 * @version    $Id: Random.php,v 1.9 2010/04/24 06:40:48 terrafrost Exp $
 * @link       http://phpseclib.sourceforge.net
 */

/**
 * Generate a random value.
 *
 * On 32-bit machines, the largest distance that can exist between $min and $max is 2**31.
 * If $min and $max are farther apart than that then the last ($max - range) numbers.
 *
 * Depending on how this is being used, it may be worth while to write a replacement.  For example,
 * a PHP-based web app that stores its data in an SQL database can collect more entropy than this function
 * can.
 *
 * @param optional Integer $min
 * @param optional Integer $max
 * @return Integer
 * @access public
 */
function crypt_random($min = 0, $max = 0x7FFFFFFF)
{
    if ($min == $max) {
        return $min;
    }

    // see http://en.wikipedia.org/wiki//dev/random
    static $urandom = true;
    if ($urandom === true) {
        // Warning's will be output unles the error suppression operator is used.  Errors such as
        // "open_basedir restriction in effect", "Permission denied", "No such file or directory", etc.
        $urandom = @fopen('/dev/urandom', 'rb');
    }
    if (!is_bool($urandom)) {
        extract(unpack('Nrandom', fread($urandom, 4)));

        // say $min = 0 and $max = 3.  if we didn't do abs() then we could have stuff like this:
        // -4 % 3 + 0 = -1, even though -1 < $min
        return abs($random) % ($max - $min) + $min;
    }

    /* Prior to PHP 4.2.0, mt_srand() had to be called before mt_rand() could be called.
       Prior to PHP 5.2.6, mt_rand()'s automatic seeding was subpar, as elaborated here:

       http://www.suspekt.org/2008/08/17/mt_srand-and-not-so-random-numbers/

       The seeding routine is pretty much ripped from PHP's own internal GENERATE_SEED() macro:

       http://svn.php.net/viewvc/php/php-src/branches/PHP_5_3_2/ext/standard/php_rand.h?view=markup */
    if (version_compare(PHP_VERSION, '5.2.5', '<=')) { 
        static $seeded;
        if (!isset($seeded)) {
            $seeded = true;
            mt_srand(fmod(time() * getmypid(), 0x7FFFFFFF) ^ fmod(1000000 * lcg_value(), 0x7FFFFFFF));
        }
    }

    static $crypto;

    // The CSPRNG's Yarrow and Fortuna periodically reseed.  This function can be reseeded by hitting F5
    // in the browser and reloading the page.

    if (!isset($crypto)) {
        $key = $iv = '';
        for ($i = 0; $i < 8; $i++) {
            $key.= pack('n', mt_rand(0, 0xFFFF));
            $iv .= pack('n', mt_rand(0, 0xFFFF));
        }
        switch (true) {
            case class_exists('Crypt_AES'):
                $crypto = new Crypt_AES(CRYPT_AES_MODE_CTR);
                break;
            case class_exists('Crypt_TripleDES'):
                $crypto = new Crypt_TripleDES(CRYPT_DES_MODE_CTR);
                break;
            case class_exists('Crypt_DES'):
                $crypto = new Crypt_DES(CRYPT_DES_MODE_CTR);
                break;
            case class_exists('Crypt_RC4'):
                $crypto = new Crypt_RC4();
                break;
            default:
                extract(unpack('Nrandom', pack('H*', sha1(mt_rand(0, 0x7FFFFFFF)))));
                return abs($random) % ($max - $min) + $min;
        }
        $crypto->setKey($key);
        $crypto->setIV($iv);
        $crypto->enableContinuousBuffer();
    }

    extract(unpack('Nrandom', $crypto->encrypt("\0\0\0\0")));
    return abs($random) % ($max - $min) + $min;
}
?>