Challenge Handshake Authentication Protocol

What Does Challenge Handshake Authentication Protocol Mean?

Challenge Handshake Authentication Protocol (CHAP) is a process of authenticating a user to a network entity, which may be any server, e.g., the web or internet service provider (ISP).


CHAP is primarily used for security purposes. For example, users provide authenticated plain text passwords when accessing remote servers, which also are authenticated prior to user access.

Techopedia Explains Challenge Handshake Authentication Protocol

CHAP ensures that the server sends a challenge to the client after the client establishes a network connection to access a web/ISP server. This challenge is received via the same network line. The client uses a hash function to calculate a specific value that is then sent to the server, which matches the incoming value against the server’s calculated value. If the values match, the client is granted server access. Otherwise, the connection is automatically terminated.

Peers randomly adopt this procedure and continuously send calculated values to an authenticating server, which, in turn, continuously authenticates peers based on calculated values.


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Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.