A new human identification protocol and coppersmith's baby-step giant-step algorithm
ACNS'10 Proceedings of the 8th international conference on Applied cryptography and network security
Cryptanalysis of the convex hull click human identification protocol
ISC'10 Proceedings of the 13th international conference on Information security
Breaking undercover: exploiting design flaws and nonuniform human behavior
Proceedings of the Seventh Symposium on Usable Privacy and Security
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Recently a new human authentication scheme called PAS (predicate-based authentication service) was proposed, which does not require the assistance of any supplementary device. The main security claim of PAS is to resist passive adversaries who can observe the whole authentication session between the human user and the remote server. In this paper we show that PAS is insecure against both brute force attack and a probabilistic attack. In particular, we show that its security against brute force attack was strongly overestimated. Furthermore, we introduce a probabilistic attack, which can break part of the password even with a very small number of observed authentication sessions. Although the proposed attack cannot completely break the password, it can downgrade the PAS system to a much weaker system similar to common OTP (one-time password) systems.