protocol used by ISPs to authenticate their clients. In this scheme, a value is sent to the client (the machine making the connection), which it uses to calculate a hash based on the value. The client sends the hash back to the server for comparison to the hash calculated by the server. This authentication method is different from PAP in that it re- authenticates on a periodic basis after the initial authentication. See Also PAP. CIFS

The Challenge-Handshake Authentication Protocol uses a challenge/response authentication mechanism where the response varies every challenge to prevent replay attacks.

An authentication method that can be used when connecting to an Internet Service Provider. CHAP allows you to login to your provider automatically, without the need for a terminal screen. It is more secure than the Password Authentication Protocol (another widely used authentication method) since it does not send passwords in text format.