Kerberos: Authentication protocol that works on the basis of tickets to allow nodes communicating
over a non-secure network to prove their identity to each other in a secure manner. It is based on a
client–server model and it provides mutual authentication both the user and the server verify each
other's identity. Messages are protected against eavesdropping and replay attacks. Builds on
symmetric keys and requires a trusted third party, and can optionally use PKI during certain phases
of authentication. Uses UDP port 88 by default, used in Active Directory from Windows 2000 and
onwards, and many Unix OS’.