CHAP is another authentication protocol that is run over serial links.

  • PPP is established.
  • The server sends a CHAP challenge to the client.
  • The client sends a response back to the server.
  • The server sends an "accept" or "reject" back to the client.

CHAP provides more security than PAP by sending an MD5-encrypted password. CHAP may also periodically verify the connection, and the server may issue a challenge to the client on a periodic basis.