Kerberos is a client-server authentication protocol that enables mutual authentication – both the user and the server verify each other’s identity – over non-secure network connections. The protocol is resistant to eavesdropping and replay attacks, and requires a trusted third party.
The Kerberos protocol uses a symmetric key derived from the user password to securely exchange a session key for the client and server to use. A server component is known as a Ticket Granting Service (TGS) then issues a security token (AKA Ticket-Granting-Ticket TGT) that can be later used by the client to gain access to different services provided by a Service Server.