Which authentication protocol is commonly used for client/server authentication in a Kerberos-based system?

• A. Kerberos
• B. RADIUS
• C. OAuth
• D. SAML

Answer: (A)

Kerberos is designed for mutual authentication between a client and a server in a trusted domain using tickets issued by a Key Distribution Center. In this setup, the client proves its identity to the KDC to obtain a ticket-granting ticket, then uses that to request a service ticket for the specific server. The server accepts the service ticket and both sides prove they possess the correct keys, enabling secure, password-safe access. This ticket-based flow is the standard way client/server authentication is handled within Kerberos, providing strong protection and enabling seamless single sign-on within the domain.

RADIUS, OAuth, and SAML serve other purposes—RADIUS is often used for network access authentication, OAuth for delegated authorization, and SAML for web-based single sign-on—but they do not handle the Kerberos-style client/server authentication mechanism.