Which item is NOT a core component of a PKI?

• A. Certificate authorities
• B. Certificates
• C. Firewall rules
• D. Certificate revocation lists

Answer: (C)

Public Key Infrastructure centers on establishing trust for digital communications: trusted authorities issue and sign certificates; those certificates bind a subject's identity to a public key; and certificate revocation lists allow you to revoke a certificate if the private key is compromised or the relationship ends. Firewall rules, while important for protecting networks, are about controlling which network traffic is allowed or blocked and do not participate in issuing, signing, or revoking certificates. Therefore firewall rules are not part of the PKI core components. For completeness, you can think of the three PKI elements as the structure that enables trust in keys and identities, with certificate authorities, certificates, and certificate revocation lists playing distinct roles in issuing, validating, and revoking credentials.