CAPTCHA: Using hard AI problems for security. (English) Zbl 1038.94551

Biham, Eli (ed.), Advances in cryptology – EUROCRYPT 2003. International conference on the theory and applications of cryptographic techniques, Warsaw, Poland, May 4–8, 2003. Proceedings. Berlin: Springer (ISBN 3-540-14039-5/pbk). Lect. Notes Comput. Sci. 2656, 294-311 (2003).
Summary: We introduce CAPTCHA, an automated test that humans can pass, but current computer programs can’t pass: any program that has high success over a CAPTCHA can be used to solve an unsolved Artificial Intelligence (AI) problem. We provide several novel constructions of CAPTCHA. Since CAPTCHA has many applications in practical security, our approach introduces a new class of hard problems that can be exploited for security purposes. Much like research in cryptography has had a positive impact on algorithms for factoring and discrete log, we hope that the use of hard AI problems for security purposes allows us to advance the field of Artificial Intelligence. We introduce two families of AI problems that can be used to construct CAPTCHA, and we show that solutions to such problems can be used for steganographic communication. CAPTCHA based on these AI problem families, then, implies a win-win situation: either the problems remain unsolved and there is a way to differentiate humans from computers, or the problems are solved and there is a way to communicate covertly on some channels.
For the entire collection see [Zbl 1020.00023].


94A60 Cryptography
68T20 Problem solving in the context of artificial intelligence (heuristics, search strategies, etc.)
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