Kerberos is a trusted third-party authentication application layer service (Layer 7 of the OSI model).
Kerberos is a secret-key network authentication protocol developed at the Massachusetts Institute of Technology (MIT) that uses the Data Encryption Standard (DES) cryptographic algorithm for encryption and authentication. In the Kerberos protocol, this trusted third party is called the key distribution center (KDC).
Figure 5-4 displays the Kerberos authentication process when a remote client initiates a remote Telnet session. (Kerberos supports Telnet, rlogin, rsh, and rcp.)