Thursday, 10 March 2011

CHAP – Challenge Handshake Authentication Protocol

An authentication method used by point-to-point protocol (PPP) servers. CHAP validates the remote client's identity at the communication session start or at any time during the session.

CHAP uses a three-way handshake after establishing a link between the client and the server.



  1. A challenge message is sent from the authenticating server to the client.
  2. The client replies with a value computed using a one-way hash function
  3. When the authenticating server receives the response it checks the value against its own calculation of the expected hash value. If the value matches, the server responds telling the user it has been successful.

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