Which service includes an authentication server, key distribution center, and ticket-granting service?

The correct answer centers on the concept of Kerberos, which is a computer network authentication protocol designed to provide secure authentication for users and services in a networked environment.

Kerberos operates using a centralized authentication server that generates and manages security tickets. The architecture includes three primary components: the authentication server, which verifies identities; the key distribution center (KDC), which holds the secret keys for users; and the ticket-granting service (TGS), which issues tickets that allow users to access various services.

This ticket-based mechanism ensures that users can authenticate without continuously sending their passwords over the network, reducing the risk of exposure. The exchange of tickets and session keys facilitates secure communication between clients and services, exemplifying Kerberos's role in enhancing security in a network.

Other listed services—such as RADIUS and TACACS—while also used for authentication, do not possess the same structure of incorporating a ticket-granting service alongside an authentication server and key distribution, making them fundamentally different from Kerberos. Similarly, LDAP primarily serves as a directory service for managing user information but does not include the same ticketing authentication framework.