Kerberos
About
Kerberos is a authentication/authorization protcol using secret-key cryptography
It allows single-sign-on system, which means that you have to type your password only once per session where Kerberos does the authentication and encrypting transparently.
Kerberos V5 is an authentication system developed at MIT
See the ticketing process for a more general comprehension of the mechanisms.
Articles Related
(Third Integration|Kerberos V5 Applications)
On many systems, Kerberos is built into the login program, and you get tickets automatically when you log in. programs, such as rsh, rcp, telnet, and rlogin, can forward copies of your tickets to the remote host. Most of these programs also automatically destroy your tickets when they exit.