private function getMacSource(Dataset $dataset)
    {
        $macParams = $this->getNormalizedMacParams($dataset, $dataset->getParam('VK_SERVICE'));
        $source = '';

        foreach ($macParams as $value) {
            $length = $this->getParamValueLength($value);
            $source .= str_pad($length, 3, '0', STR_PAD_LEFT) . $value;
        }

        return $source;
    }