The Holey Grail: A special score function for non-binary traitor tracing

We study collusion-resistant traitor tracing in the simple decoder approach, i.e. assignment of scores for each user separately. We introduce a new score function for non-binary bias-based traitor tracing. It has three special properties that have long been sought after: (i) The expected score of an innocent user is zero in each content position. (ii) The variance of an innocent user\u27s score is~1 in each content position. (iii) The expectation of the coalition\u27s score does not depend on the collusion strategy. We also find a continuous bias distribution that optimizes the asymptotic (large coalition) performance. In the case of a binary alphabet our scheme reduces exactly to the symmetrized Tardos traitor tracing system. Unfortunately, the asymptotic fingerprinting rate of our new scheme decreases with growing alphabet size. We regret to inform you that this grail has holes

Optimal sequential fingerprinting: Wald vs. Tardos

We study sequential collusion-resistant fingerprinting, where the fingerprinting code is generated in advance but accusations may be made between rounds, and show that in this setting both the dynamic Tardos scheme and schemes building upon Wald's sequential probability ratio test (SPRT) are asymptotically optimal. We further compare these two approaches to sequential fingerprinting, highlighting differences between the two schemes. Based on these differences, we argue that Wald's scheme should in general be preferred over the dynamic Tardos scheme, even though both schemes have their merits. As a side result, we derive an optimal sequential group testing method for the classical model, which can easily be generalized to different group testing models.Comment: 12 pages, 10 figure

Security and robustness constraints for spread-spectrum Tardos fingerprinting

International audienceThis paper presents a practical analysis of the impact of robustness and security on Tardos' collusion-secure fingerprinting codes using spread-spectrum watermarking modulations. In this framework, we assume that the coalition has to face an embedding scheme of given security level and consequently has to suffer a probability of wrongly estimating their embedded symbols. We recall the Worst Case Attack associated to this probability, e.g. the optimal attack which minimises the mutual information between the sequence of a colluder and the pirated one. For a given achievable rate of the Tardos' fingerprinting model, we compare the Improved Spread-Spectrum embedding versus a new secure embedding (called rho-Circular Watermarking) considering the AWGN channel. We show that secure embeddings are more immune to decoding errors than non-secure ones while keeping the same fingerprinting capacity

Estimating the minimal length of tardos code

Abstract. This paper estimates the minimal length of a binary probabilistic traitor tracing code. We consider the code construction proposed by G. Tardos in 2003, with the symmetric accusation function as improved by B. Skoric et al. The length estimation is based on two pillars. First, we consider the Worst Case Attack that a group of c colluders can lead. This attack minimizes the mutual information between the code sequence of a colluder and the pirated sequence. Second, an algorithm pertaining to the field of rare event analysis is presented in order to estimate the probabilities of error: the probability that an innocent user is framed, and the probabilities that all colluders are missed. Therefore, for a given collusion size, we are able to estimate the minimal length of the code satisfying some error probabilities constraints. This estimation is far lower than the known lower bounds