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1 Introduction

Kerberos V5 is an authentication system developed at MIT. Kerberos is named for the three-headed watchdog from Greek mythology, who guarded the entrance to the underworld.

Under Kerberos, a client (generally either a user or a service) sends a request for a ticket to the Key Distribution Center (KDC). The KDC creates a ticket-granting ticket (TGT) for the client, encrypts it using the client's password as the key, and sends the encrypted TGT back to the client. The client then attempts to decrypt the TGT, using its password. If the client successfully decrypts the TGT (i.e., if the client gave the correct password), it keeps the decrypted TGT, which indicates proof of the client's identity.

The TGT, which expires at a specified time, permits the client to obtain additional tickets, which give permission for specific services. The requesting and granting of these additional tickets is user-transparent.

Since Kerberos negotiates authenticated, and optionally encrypted, communications between two points anywhere on the internet, it provides a layer of security that is not dependent on which side of a firewall either client is on. Since studies have shown that half of the computer security breaches in industry happen from inside firewalls, MIT's Kerberos V5 plays a vital role in maintaining your network security.

The Kerberos V5 package is designed to be easy to use. Most of the commands are nearly identical to UNIX network programs you already use. Kerberos V5 is a single-sign-on system, which means that you have to type your password only once per session, and Kerberos does the authenticating and encrypting transparently.