public function getHiddenFields()
    {
        $apiId     = '<input type="hidden" name="secure[api_id]"    value="' . $this->getApiId() . '" />';
        $timestamp = '<input type="hidden" name="secure[timestamp]" value="' . $this->getTimeStamp() . '" />';
        $nonce     = '<input type="hidden" name="secure[nonce]"     value="' . $this->getNonce() . '" />';
        $data      = '<input type="hidden" name="secure[data]"      value="' . $this->getDataStringEncoded() . '" />';
        $signature = '<input type="hidden" name="secure[signature]" value="' . $this->getRequestSignature() . '" />';

        return "$apiId\n$timestamp\n$nonce\n$data\n$signature\n";
    }