Tracing traitors: a selective survey

Digital media provide higher portability, storage and communication efficiency, and accuracy of data. However digital objects can be easily and accurately copied. This allows unauthorized reproduction and distribution of copyrighted objects, hence bypassing the ownership and intellectual property rights of owners, creators and distributors of the object. Protection of media data such as movies, music and multimedia data against illegal copying and re-distribution has been one of the greatest challenges of digital content distribution. Protection becomes exceedingly hard if a group of users combine their privileges to overcome the protection mechanism of the system. A range of techniques have been proposed to "mark" the content, or the player of the content, so that pirate digital objects, or the illegal player, can be traced and at least one of the colluders be identified. We review a range of techniques and constructions that have been proposed in recent years and used in applications such as pay-TV, digital broadcasting and content distribution systems, as well as digital storage systems such as compact disks. We will point out limitations of existing methods and discuss challenges and directions for future research.