public function transactionData($params)
    {
        Util::verifyKeys(
                self::$_transactionSignature,
                $params
                );
        $params["kind"] = TransparentRedirect::CREATE_TRANSACTION;
        $transactionType = isset($params['transaction']['type']) ?
            $params['transaction']['type'] :
            null;
        if ($transactionType != Transaction::SALE && $transactionType != Transaction::CREDIT) {
           throw new InvalidArgumentException(
                   'expected transaction[type] of sale or credit, was: ' .
                   $transactionType
                   );
        }

        return $this->_data($params);
    }