<?php

/*

This file is part of PHPOLL.

    PHPOLL is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    PHPOLL is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with PHPOLL; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

*/

// THANKS TO Alexander Valyalkin from PHP.net manual and forum for the functions in this file

function get_rnd_iv($iv_len)
{
   $iv = '';
   while ($iv_len-- > 0) {
       $iv .= chr(mt_rand() & 0xff);
   }
   return $iv;
}

function md5_encrypt($plain_text, $password, $iv_len = 16)
{
   $plain_text .= "\x13";
   $n = strlen($plain_text);
   if ($n % 16) $plain_text .= str_repeat("\0", 16 - ($n % 16));
   $i = 0;
   $enc_text = get_rnd_iv($iv_len);
   $iv = substr($password ^ $enc_text, 0, 512);
   while ($i < $n) {
       $block = substr($plain_text, $i, 16) ^ pack('H*', md5($iv));
       $enc_text .= $block;
       $iv = substr($block . $iv, 0, 512) ^ $password;
       $i += 16;
   }
   return base64_encode($enc_text);
}

function md5_decrypt($enc_text, $password, $iv_len = 16)
{
   $enc_text = base64_decode($enc_text);
   $n = strlen($enc_text);
   $i = $iv_len;
   $plain_text = '';
   $iv = substr($password ^ substr($enc_text, 0, $iv_len), 0, 512);
   while ($i < $n) {
       $block = substr($enc_text, $i, 16);
       $plain_text .= $block ^ pack('H*', md5($iv));
       $iv = substr($block . $iv, 0, 512) ^ $password;
       $i += 16;
   }
   return preg_replace('/\\x13\\x00*$/', '', $plain_text);
}

?>