CHAP Challenge Handshake Authentication Protocol, CHAP, is a type of authentication used to verify the identity of a user who tries to log on to a PPP-server. After the link is established, the authenticator (typically a network server) sends the originator (the client program) a challenge to send some private information (a response). Both the server and client program then calculate a response to the challenge. At this point, the server compares the response it gets from the client with the answer it has generated locally and acknowledges the client if they arrive at the same result. If the values do not match, the connection is usually terminated. CHAP not only requires the client to authenticate itself at startup time, but sends challenges at regular intervals to make sure the client has not been replaced by an intruder.
