Kerberos: The Definitive Guide

Origins

The word Kerberos originates from Greek mythology, which contains the legend of Cerberus. Cerberus guarded the realm of the underworld, ruled by Hades and his wife, Persephone. What Cerberus looked like depends on whom you ask; Hesiod claims that Cerberus has fifty heads, while Apollodorus describes him as a strange mixture of creatures with three dog-shaped heads, a serpent as a tail, and heads of snakes over his back. Cerberus is most often pictured as a creature with three heads. Either way, Cerberus was a vicious creature that few dared to challenge.

The Greeks believed that when a person dies, his soul is sent to Hades to spend eternity. While all souls were sent to Hades, those people who had led a good life would be spared the eternal punishment that those who had not would have to endure. Cerberus, as the gatekeeper to Hades, ensured that only the souls of the dead entered Hades, and he ensured that souls could not escape once inside.

As the gatekeeper to Hades, Cerberus authenticated those who attempted to enter (to determine whether they were dead or alive) and used that authentication to determine whether to allow access or not. Just like the ancient Cerberus, the modern Kerberos authenticates those users who attempt to access network resources.

Like every other great figure in mythology, Cerberus had a fatal flaw that enabled some clever people to pass through Cerberus to Hades. We’ll revisit the legend and discuss one such story and its modern counterparts in Chapter 6.

Finally, if the ancient mythological character was named Cerberus, why is the modern authentication system called Kerberos? Simply put, they are just different spellings of the same word. In order to provide a distinction between the ancient mythology and the present-day software system, we will refer to the mythological character as Cerberus and the modern software system as Kerberos.