Kerberos has two purposes: security and authentication. On most computer systems, a password is used to prove a user's identity; on a distributed network system, like Athena, this password must be transmitted over the network, from the workstation being used, to any other machines containing files or programs the user wants access to. Because this password is the one secret piece of information that identifies a user, anyone knowing a user's password can effectively be that user on Athena, reading their files, sending mail as that user, etc. Obviously, it is therefore necessary to prevent anyone from intercepting or eavesdropping on the transmitted password. In addition, it is necessary to provide a means of authenticating users: any time a user requests a service, such as mail on, they must prove their identity. This is done with Kerberos, and this is why we get our mail and no e else's