One of two authentication protocols (PAP and CHAP) used by OpenROUTE Networks routers. CHAP is the Challenge Handshake Authentication Protocol, which requires the local router to send a challenge to the connecting router. The router anticipates a specific response. If the connecting router answers with the anticipated response, communication between the two routers continues, if not, the communication channel shuts down.

a challenge-response LCP authentication protocol resistant to playback attacks. CHAP runs after LCP negotiation is complete but before any NCPs are started.

Log-in security procedure for dial-in access. Rather than send an unencrypted password, a random number is sent to the client as a challenge. The challenge is one-way hashed with the password, and the result is sent back to the server. The server does the same with its copy of the password and verifies that it gets the same result to authenticate the user, abbreviated as CHAP.