Kerberos is a network authentication protocol. It is designed to provide strong authentication for client/server applications by using secret-key cryptography. A free implementation of this protocol is available from the Massachusetts Institute of Technology.
Password Authentication Protocol (PAP) is a simple user authentication protocol that does not encrypt the data and sends the password and username to the authentication server as plain text. PAP is very vulnerable to being read from the Point-to-Point Protocol (PPP) data packets exchanged between the authentication server and the user’s machine.