Paper 2012/667

False Negative probabilities in Tardos codes

Antonino Simone and Boris Skoric

Abstract

Forensic watermarking is the application of digital watermarks for the purpose of tracing unauthorized redistribution of content. The most powerful type of attack on watermarks is the collusion attack, in which multiple users compare their differently watermarked versions of the same content. Collusion-resistant codes have been developed against these attacks. One of the most famous such codes is the Tardos code. It has the asymptotically optimal property that it can resist c attackers with a code of length proportional to c^2. Determining error rates for the Tardos code and its various extensions and generalizations turns out to be a nontrivial problem. In recent work we developed an approach called the Convolution and Series Expansion (CSE) method to accurately compute false positive accusation probabilities. In this paper we extend the CSE method in order to make it possible to compute false negative accusation probabilities as well.