Which authentication method involves periodic re-authentication through a hash?

The authentication method that involves periodic re-authentication through a hash is CHAP (Challenge Handshake Authentication Protocol). CHAP enhances security by employing a three-way handshake process that utilizes a challenge-response mechanism. In this process, the authenticator sends a challenge to the client, which then responds with a hash value generated from the challenge and the client's password.

This method distinguishes itself from others by requiring the client to re-authenticate periodically. Each time a network connection is initiated, the server issues a new challenge, and the client must respond correctly to maintain the connection. This periodic re-authentication helps to prevent "replay attacks," where an attacker could attempt to use previously intercepted authentication responses.

In contrast, other methods like PAP (Password Authentication Protocol) and SPAP (Shiva Password Authentication Protocol) do not provide this level of security, as they typically involve sending passwords in plain text or, in the case of SPAP, basic hashing but without periodic challenges. EAP (Extensible Authentication Protocol) is more of a framework for multiple authentication methods rather than a specific method itself. Thus, CHAP is recognized for its effectiveness in maintaining secure and ongoing authentication through hashing.