http://www.rfc-editor.org/rfc/rfc1994.txt
RFC 1994: PPP Challenge Handshake Authentication Protocol (CHAP), W. Simpson1996-08-01T23:00:00-00:00This document defines a method for Authentication using PPP, which uses a random Challenge, with a cryptographically hashed Response which depends upon the Challenge and a secret key. [STANDARDS-TRACK]