From Wikipedia
Kerberos is the name of a computer network authentication protocol, which allows individuals communicating over a non-secure network to prove their identity to one another in a secure manner. It is also a suite of free software published by Massachusetts Institute of Technology (MIT) that implements this protocol. Its designers aimed primarily at a client-server model, and it provides mutual authentication — both the user and the server verify each other's identity. Kerberos protocol messages are protected against eavesdropping and replay attacks.
Kerberos builds on symmetric key cryptography and requires a trusted third party. Extensions to Kerberos can provide for the use of public-key cryptography during certain phases of authentication.
In Greek mythology, Kerberos (Greek Κέρβερος, Kérberos, the daemon or ker of Erebos) was the hound of Hades, a monstrous three-headed dog with a snake for a tail (sometimes said to have 50 or 100 heads) who analogs in other cultures are hellhounds. Other hell hounds included Orthus, his two headed brother. Cerberus guarded the gate to Hades and ensured that spirits of the dead could enter, but none could exit (additionally, no living person was to come into Hades). Among his siblings are Chimera and the Hydra. He is the offspring of Echidna and Typhon. In Dante's Inferno, he is described as having a human head. This symbolizes the possibility of Cerberus being more human than animal.