    protected function hmac($data, $key)
    {
        if (function_exists('hash_hmac')) {
            return hash_hmac('md5', $data, $key);
        }

        // The following borrowed from
        // http://php.net/manual/en/function.mhash.php#27225

        // RFC 2104 HMAC implementation for php.
        // Creates an md5 HMAC.
        // Eliminates the need to install mhash to compute a HMAC
        // by Lance Rushing

        $bytelen = 64; // byte length for md5
        if (strlen($key) > $bytelen) {
            $key = pack('H*', md5($key));
        }
        $key = str_pad($key, $bytelen, chr(0x00));
        $ipad = str_pad('', $bytelen, chr(0x36));
        $opad = str_pad('', $bytelen, chr(0x5c));
        $k_ipad = $key ^ $ipad;
        $k_opad = $key ^ $opad;

        return md5($k_opad . pack('H*', md5($k_ipad . $data)));
    }
The product receives input or data, but it does
        not validate or incorrectly validates that the input has the
        properties that are required to process the data safely and
        correctly.