Challenge–response authentication

In computer security, challenge–response authentication is a family of protocols in which one party presents a question ('challenge') and another party must provide a valid answer ('response') to be authenticated. In computer security, challenge–response authentication is a family of protocols in which one party presents a question ('challenge') and another party must provide a valid answer ('response') to be authenticated. The simplest example of a challenge–response protocol is password authentication, where the challenge is asking for the password and the valid response is the correct password.