Kerberos (protocol)
Kerberos uses as its basis the Needham-Schroeder protocol. It makes use of a trusted third party authentication known as "key distribution center (KDC)", which consists of two logically separate parts: an Authentication Server (AS) and a Ticket Granting Server (TGS). Kerberos works on the basis of "tickets" (called Kerberos tickets) which serve to prove the identity of users.