A challenge-response test is a test involving a set of questions (or "challenges"), that the person or other entity has to answer in order to pass the test. If the person or entity provides an adequate response to the challenges then the it is deemed that the person or entity has passed the test.
The concept appears in computer security, where challenge-response authentication relies on the possession of a secret of some sort to perform authentication. A very simple example is asking for a password, where the challenge is asking for the password, and the adequate response is the correct password. More sophisticated algorithms include CRAM-MD5, or ssh's challenge-response system based on RSA [1].
The Turing test for artificial intelligence is a good example of challenge-response. A variant is Captchas, where the challenge is usually to identify letters in an image.
One real world example would be as in movies where in order to gain access to a certain location the door-man says something and the person attempting to gain access has to say the adequate response.
Many other types of challenge-response tests exist, as well.Challenge-response in computer security
Examples in other contexts
