In a public key cryptographic system, which of the following is the PRIMARY requirement to address the risk of man-in-the-middle attacks through spoofing?

Strong encryption algorithms protect the confidentiality of data but do not, by themselves, verify the identity of the communicating parties, which is crucial for preventing spoofing in MITM attacks.

Kerberos is a strong symmetric-key authentication system primarily used within a trusted domain, not typically for verifying identities across public, untrusted networks in a public key infrastructure context.

A registration authority (RA) assists the CA by verifying identities, but the CA itself is the entity that issues and signs the certificates, providing the trust anchor necessary to prevent spoofing.

A Certificate Authority (CA) is a trusted entity that issues digital certificates, binding a public key to an authenticated identity. This allows users to verify that a public key truly belongs to the claimed entity, thereby preventing an attacker from spoofing an identity and intercepting communications in a man-in-the-middle attack.