public static function decrypt($string, $key) {
        $result = '';
        $string = base64_decode($string);

        for ($i=0; $i<strlen($string); $i++) {
            $char = substr($string, $i, 1);
            $keychar = substr($key, ($i % strlen($key))-1, 1);
            $char = chr(ord($char)-ord($keychar));
            $result .= $char;
        }

        return $result;
    }