Sliding-window dynamic frameproof codes
Designs, Codes and Cryptography
INDOCRYPT'07 Proceedings of the cryptology 8th international conference on Progress in cryptology
Identification algorithms for sequential traitor tracing
INDOCRYPT'04 Proceedings of the 5th international conference on Cryptology in India
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The notion of traitor tracing was introduced by Chor, Fiat, and Naor [Tracing Traitors, Lecture Notes in Comput. Sci. 839, 1994, pp. 257--270] in order to combat piracy scenarios. Recently, Fiat and Tassa [ Tracing Traitors, Lecture Notes in Comput. Sci. 1666, 1999, pp. 354--371] proposed a dynamic traitor tracing scenario, in which the algorithm adapts dynamically according to the responses of the pirate. Let n be the number of users and p the number of traitors.Our main result is an algorithm which locates p traitors, even if p is unknown, using a watermarking alphabet of size p+1 and an optimal number of $\Theta(p^2 + p\log n)$ rounds. This improves the exponential number of rounds achieved by Fiat and Tassa in this case. We also present two algorithms that use a larger alphabet: for an alphabet of size p+c+1, $c\geq1$, an algorithm that uses O(p2/c+ p log n) rounds; for an alphabet of size pc+1, an algorithm that uses O(p logcn) rounds.Our final result is a lower bound of $\Omega(p^2/c+p\log_{c+1}n)$ rounds for any algorithm that uses an alphabet of size p+c, assuming that p is not known in advance.