Challenge-Response Authentication

Challenge-Response Authentication (CRA) is a security mechanism used to verify the identity of an entity before granting access to a system or service. It operates by exchanging a series of challenges and corresponding responses between the authenticating entity (usually a server or host) and the entity seeking authentication (usually a client or user).

In CRA, the authenticator (server) poses a challenge, which is a random or predetermined value, to the entity seeking authentication. The client then generates a response based on the challenge and its own secret information (such as a password or cryptographic keys) using a specific algorithm. This response is sent back to the server. The server, equipped with the same secret information and algorithm, independently computes the expected response based on the challenge it generated. If the response from the client matches the expected response on the server, authentication is successful, otherwise, access is denied. Challenge-Response Authentication helps protect against various types of attacks like replay attacks, where someone captures a previous successful authentication attempt and tries to reuse it later.