public function decrypt($string)
  {
    $string = base64_decode($string);
    $decryp = "";
    $length = strlen($string);
    $string .= str_repeat(chr(0), (8-($length%8))%8);

    for($i = 0; $i < $length; $i += 8)
    {
      list(,$xl,$xr) = unpack("N2", substr($string, $i, 8));
      $this->decipher($xl, $xr);
      $decryp .= pack("N2", $xl, $xr);
    }

    return trim($decryp);
  }