Paper 2007/041

Symmetric Tardos fingerprinting codes for arbitrary alphabet sizes

B. Skoric, S. Katzenbeisser, and M. U. Celik

Abstract

Fingerprinting provides a means of tracing unauthorized redistribution of digital data by individually marking each authorized copy with a personalized serial number. In order to prevent a group of users from collectively escaping identification, collusion-secure fingerprinting codes have been proposed. In this paper, we introduce a new construction of a collusion-secure fingerprinting code which is similar to a recent construction by Tardos but achieves shorter code lengths and allows for codes over arbitrary alphabets. For binary alphabets, $$ users and a false accusation probability of $$, a code length of $$ is provably sufficient to withstand collusion attacks of at most $$ colluders. This improves Tardos' construction by a factor of $$. Furthermore, invoking the Central Limit Theorem we show that even a code length of $$ is sufficient in most cases. For $$-ary alphabets, assuming the restricted digit model, the code size can be further reduced. Numerical results show that a reduction of 35\% is achievable for $$ and 80\% for~$$.