Traitor Tracing
Teddy Furon · 2022
This chapter presents the problem of traitor tracing and the most efficient solution known, Tardos codes. Tracing codes form an application overlay to the transmission layer by watermarking: a codeword is generated for each user, and then inserted, by watermarking, into a confidential document to be shared. The chapter introduces the main components: code construction, collusion strategy, accusation with a simple decoder, based on a score function and thresholding. It provides a simplified proof of Tardos’ original scheme, presents the many extensions found in the literature. The chapter explains the choices made in Tardos and the improvements offered in Škorić et al. Among all of the further developments of the Tardos code, it presents new, more powerful score functions for binary codes.