protected function decrypt($response)
    {

        $hashSequence = "status||||||udf5|udf4|udf3|udf2|udf1|email|firstname|productinfo|amount|txnid|key";
        $hashVarsSeq = explode('|', $hashSequence);
        $hash_string = $this->salt."|";

        foreach($hashVarsSeq as $hash_var) {
            $hash_string .= isset($response[$hash_var]) ? $response[$hash_var] : '';
            $hash_string .= '|';
        }

        $hash_string = trim($hash_string,'|');

        return strtolower(hash('sha512', $hash_string));
    }