J Jan-Jaap Oosterwijk

Optimal suspicion functions for tardos traitor tracing schemes

We investigate alternative suspicion functions for Tardos traitor tracing schemes. In the simple decoder approach (computation of a score for every user independently) we derive suspicion functions that optimize a performance indicator related to the sufficient code length l in the limit of large coalition size c. Our results hold for the Restricted-Digit Model as well as the Combined-Digit Model. The scores depend on information that is usually not available to the tracer -- the attack strategy or the tallies of the symbols received by the colluders. We discuss how such results can be used in realistic contexts. We study several combinations of coalition attack strategy versus suspicion function optimized against some attack (another attack or the same). In many of these combinations the usual scaling l \propto c2 is replaced by a lower power of c, e.g. c3/2. We find that the interleaving strategy is an especially powerful attack, and the suspicion function tailored against interleaving is effective against all considered attacks.

Dynamic traitor tracing for arbitrary alphabets: Divide and conquer

We give a generic divide-and-conquer approach for constructing collusion-resistant probabilistic dynamic traitor tracing schemes with larger alphabets from schemes with smaller alphabets. This construction offers a linear tradeoff between the alphabet size and the codelength. In particular, we show that applying our results to the binary dynamic Tardos scheme of Laarhoven et al. leads to schemes that are shorter by a factor equal to half the alphabet size. Asymptotically, these codelengths correspond, up to a constant factor, to the fingerprinting capacity for static probabilistic schemes. This gives a hierarchy of probabilistic dynamic traitor tracing schemes, and bridges the gap between the low bandwidth, high codelength scheme of Laarhoven et al. and the high bandwidth, low codelength scheme of Fiat and Tassa.

A Capacity-Achieving Simple Decoder for Bias-Based Traitor Tracing Schemes

We investigate alternative suspicion functions for bias-based traitor tracing schemes, and present a practical construction of a simple decoder that attains capacity in the limit of large coalition size c. We derive optimal suspicion functions in both the restricted-digit model and the combined-digit model. These functions depend on information that is usually not available to the tracer-the attack strategy or the tallies of the symbols received by the colluders. We discuss how such results can be used in realistic contexts. We study several combinations of coalition attack strategy versus suspicion function optimized against some attack (another attack or the same). In many of these combinations, the usual codelength scaling ℓ ∝ c2 changes to a lower power of c, e.g., c3/2. We find that the interleaving strategy is an especially powerful attack. The suspicion function tailored against interleaving is the key ingredient of the capacity-achieving construction.

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

Tuple decoders for traitor tracing schemes

m\propto c_0^2

A capacity-achieving simple decoder for bias-based traitor tracing schemes

m∝c02, where

Riding the Saddle Point : asymptotics of the capacity-achieving simple decoder for bias-based traitor tracing

c_0