A certificate authority (CA) is critical in a public key cryptographic system for mitigating man-in-the-middle (MITM) attacks. It ensures that public keys are authentic by issuing digital certificates, which bind a public key to an entity. The CA's role in verifying identities and providing trust anchors prevents attackers from spoofing keys. * Strong Encryption Algorithms (Option A):Encryption ensures confidentiality but does not address spoofing risks. * Kerberos Authentication (Option B):Useful for mutual authentication but not central to public key infrastructure (PKI). * Registration Authority (Option C):Supports the CA but does not directly prevent MITM attacks. Reference:ISACA CISA Review Manual, Job Practice Area 4: Protection of Information Assets.