Binary and q-ary Tardos codes, revisited

The Tardos code is a much studied collusion-resistant fingerprinting code, with the special property that it has asymptotically optimal length m ¿ c^2_0, where c_0 is the number of colluders. In this paper we give alternative security proofs for the Tardos code, working with the assumption that the strongest coalition strategy is position-independent. We employ the Bernstein inequality and Bennett inequality instead of the typically used Markov inequality. This proof technique requires fewer steps and slightly improves the tightness of the bound on the false negative error probability. We present new results on code length optimization, for both small and asymptotically large coalition sizes. Keywords: Traitor tracing; Tardos fingerprinting; Collusio