![]() ![]() To address the insecure channel problem, a more sophisticated approach is necessary. Non-cryptographic authentication was generally adequate in the days before the Internet, when the user could be sure that the system asking for the password was really the system they were trying to access, and that nobody was likely to be eavesdropping on the communication channel to observe the password being entered. The distortion was designed to make automated optical character recognition (OCR) difficult and prevent a computer program from passing as a human. In early CAPTCHAs, the challenge sent to the viewer was a distorted image of some text, and the viewer responded by typing in that text. CAPTCHAs, for example, are a variant on the Turing test, meant to determine whether a viewer of a Web or mobile application is a real person. Other non-cryptographic protocols Ĭhallenge-response protocols are also used to assert things other than knowledge of a secret value. In the real world, the algorithm would be much more complex.) Bob issues a different challenge each time, and thus knowing a previous correct response (even if it is not "hidden" by the means of communication used between Alice and Bob) is of no use. (The correct response might be as simple as "63x83z", with the algorithm changing each character of the challenge using a Caesar cipher. The "fit" is determined by an algorithm agreed upon by Bob and Alice. Alice must respond with the one string of characters which "fits" the challenge Bob issued. ![]() Bob issues a challenge, perhaps "52w72y". Say Bob is controlling access to some resource. For added security, each set of codes is only valid for a particular time period which is ordinarily 24 hours.Ī more interesting challenge-response technique works as follows. TRIAD includes a list of three-letter challenge codes, which the verifier is supposed to choose randomly from, and random three-letter responses to them. military uses the AKAC-1553 TRIAD numeral cipher to authenticate and encrypt some communications. Assuming that the passwords are chosen independently, an adversary who intercepts one challenge-response message pair has no clues to help with a different challenge at a different time.įor example, when other communications security methods are unavailable, the U.S. The verifier can then present an identifier, and the prover must respond with the correct password for that identifier. One solution is to issue multiple passwords, each of them marked with an identifier. 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.Īn adversary who can eavesdrop on a password authentication can then authenticate itself by reusing the intercepted password. 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. Please help improve this article by introducing citations to additional sources.įind sources: "Challenge–response authentication" – news Relevant discussion may be found on the talk page. This article relies largely or entirely on a single source. ![]()
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