public static function simpleEncode($string, $passkey = null)
    {
        $key = $passkey;
        if (!isset($passkey) || empty($passkey)) {
            $key = self::generateServerSpecificHash();
        }

        $result = '';
        for ($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 base64_encode($result);
    }