Which XML-based protocol enhances security for online credit and debit card transactions?

3-D Secure is an XML-based protocol designed specifically to enhance security for online credit and debit card transactions. It functions as an additional layer of authentication, helping to prevent fraud during online purchases. When a user attempts to make a transaction, 3-D Secure prompts them to enter a password or a verification code sent to their registered mobile device. This verification step ensures that the person making the transaction is the legitimate cardholder.

The protocol is supported by various credit card networks, such as Visa's Verified by Visa and Mastercard's SecureCode, making it widely recognized among merchants and consumers. By requiring this extra validation, 3-D Secure helps reduce the risk of unauthorized transactions and chargebacks, thereby fostering a safer online shopping environment.

In contrast, the other options represent different security measures or protocols but do not specifically focus on enhancing security for online credit and debit card transactions in the same targeted manner as 3-D Secure does.