protected function encrypt()
    {
        $this->hash = '';
        $hashSequence = "key|txnid|amount|productinfo|firstname|email|udf1|udf2|udf3|udf4|udf5|udf6|udf7|udf8|udf9|udf10";
        $hashVarsSeq = explode('|', $hashSequence);
        $hash_string = '';

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

        $hash_string .= $this->salt;
        $this->hash = strtolower(hash('sha512', $hash_string));
    }