public function getMd5Hash()
    {
        $transactionReference = $this->httpRequest->request->get('x_trans_id');
        $amount = $this->httpRequest->request->get('x_amount');

        $key = array(
            $this->getHashSecret(),
            $this->getApiLoginId(),
            $transactionReference,
            $amount,
        );

        return md5(implode('', $key));
    }