protected function generateChecksumForPostback()
    {
        return sha1(
                sprintf("%s|%s|%s|%s|%s|%s|%s|%s|%s|%s|%s|%s", $this->_secretCode, $this->_merchantID, $this->data->status, $this->data->statusCode, $this->data->orderID, $this->data->paymentID, $this->data->reference, $this->data->transactionID, $this->data->amount, $this->data->currency, $this->data->duration, $this->data->consumerIPAddress
                )
        );
    }