Which protocol uses symmetric encryption and the Key Distribution Center for authentication functions?

The correct answer is Kerberos, which is a network authentication protocol that uses symmetric encryption to secure communications. In Kerberos, a Key Distribution Center (KDC) plays a critical role in authenticating users and services. The KDC consists of two main components: the Authentication Service (AS) and the Ticket Granting Service (TGS). When a user wants to access a service, the user first authenticates to the KDC, which then issues a ticket. This ticket is encrypted and contains a session key that allows the user and the service to establish a secure connection without needing to repeatedly transmit sensitive credentials.

Kerberos utilizes a clock synchronization mechanism to help ensure the security of the tickets, preventing replay attacks and ensuring that tickets are only valid for a limited time. The use of symmetric encryption means that the same key is used for both encryption and decryption, which is efficient and effective for the environment it is designed for, particularly in secure network environments.

In contrast, the other options presented do not utilize the KDC or the same method of symmetric encryption in their authentication processes. EAP-MD5 is primarily a challenge-response mechanism without a full authentication framework like that of Kerberos. EAP-TTLS is an extension of the EAP