What does the requirement of "two-factor authentication" entail according to PCI DSS?

The requirement of "two-factor authentication" in the context of PCI DSS entails a security process in which a user must provide two different authentication factors to verify their identity. This enhances security by requiring two distinct forms of verification, making it significantly more difficult for unauthorized users to gain access to sensitive data or systems.

The two factors typically involve something the user knows (like a password or PIN) and something the user possesses (such as a smartphone app for generating a time-based one-time password or a hardware token). By requiring both factors, it mitigates the risk of identity theft and enhances the integrity of authentication processes, aligning with PCI DSS's goal of safeguarding cardholder data.

In contrast, the other options do not accurately represent the two-factor authentication requirement. The idea of two users verifying each other’s identities does not align with individual authentication processes. An annual password change may be a good security practice but does not fulfill the two-factor authentication requirement. Lastly, single sign-on systems typically do not involve multiple steps for verification, which is contrary to the very nature of two-factor authentication.