In computing, the Challenge-Handshake Authentication Protocol (CHAP) validates a customer or network host to an authenticating entity. CHAP gives security against replay attacks by the peer through the utilization of an incrementally changing identifier and of a variable challenge-value. CHAP needs that both the customer and server know the plaintext of the secret, it is never transmitted over the network. CHAP gives better security when contrasted with Password Authentication Protocol which is vulnerable for both these reasons. It is based on the foundation of a shared secret however to support a service, the individual mentioning support and the assistance conduct a cryptographic exchange, or “handshake”.