Is correct because that is exactly what Kerberos is. The following answers are incorrect: A three-headed dog from Egyptian mythology. Is incorrect because we are dealing with Information Security and not the
Egyptian mythology but the Greek Mythology. A security model. Is incorrect because Kerberos is an authentication protocol and not just a security model. A remote authentication dial in user server. Is incorrect because Kerberos is not a remote authentication dial in user server that would be called RADIUS.