CHAP 
Challenge-Handshake Authentication Protocol 
One of the two main authentication protocols used to verify a user's name and password for PPP Internet connections. CHAP is more secure than the more basic PAP method because it performs a three-way "handshake" during the initial link establishment between the home and remote machines. The three-step process works like this: The authenticator (the secure network server you're trying to connect to) sends the client (your computer) a key with which to encrypt your name and password. Your computer sends the encrypted info to the server. Then the server authenticates you. The server can also repeat the authentication any time after the link has been established. With PAP, your name and password are not encrypted.