Which of the following does the PA-DSS apply to?

The PA-DSS (Payment Application Data Security Standard) specifically applies to third-party, "off-the-shelf" payment applications. These applications are purchased, installed, and used by merchants to process cardholder data. The goal of PA-DSS is to ensure that these payment applications are developed in a manner that protects sensitive cardholder information and complies with the security requirements established by the PCI SSC (Payment Card Industry Security Standards Council).

Third-party payment applications, as governed by PA-DSS, are held to standards that seek to prevent credit card data breaches, ensuring that the applications have robust security measures such as encryption, protecting cardholder data, and secure storage methods. By adhering to PA-DSS requirements, these vendors can demonstrate that their applications are not only functionally effective but also secure enough to minimize vulnerabilities and risks to sensitive payment data.

In-house developed payment applications, merchant processing systems, and online payment gateways do not fall under the scope of PA-DSS in the same way, as these may have different compliance frameworks or standards to adhere to, like building in PCI DSS compliance into their development or operational practices.