Which concept informs how to decide on the legitimacy of a digital certificate?

• A. A method for automating infrastructure changes.
• B. Informs applications how to decide on the legitimacy of a digital certificate.
• C. A technique for converting data to symbols.
• D. A policy governing user access control.

Answer: (B)

Certificate validation within a Public Key Infrastructure guides how applications decide a certificate’s legitimacy. It defines the checks used to trust a certificate: verify the digital signature with the issuer’s public key and follow the chain of trust to a trusted root, ensure the certificate is currently valid (not expired), check revocation status via OCSP or CRLs, and confirm the certificate’s subject matches the intended domain or entity. It also considers key usage and policy constraints to ensure the certificate is appropriate for its purpose. When these checks all pass, the certificate is trusted; if any fail, it’s rejected or flagged. The other options refer to unrelated topics—automating infrastructure changes, encoding data, or access control policies—and don’t describe how trust in a certificate is established.