In the last few years, a large number of schemes have been proposed for hiding copyright marks and other information in digital pictures, video, audio and other multimedia objects. We describe some contenders that have appeared in the research literature and in the field; we then present a number of attacks that enable the information hidden by them to be removed or otherwise rendered unusable. 1 Information Hiding Applications The last few years have seen rapidly growing interest in ways to hide information in other information. A number of factors contributed to this. Fears that copyright would be eroded by the ease with which digital media could be copied led people to study ways of embedding hidden copyright marks and serial numbers in audio and video; concern that privacy would be eroded led to work on electronic cash, anonymous remailers, digital elections and techniques for making mobile computer users harder for third parties to trace; and there remain the traditional ‘military’ concerns about hiding one’s own traffic while making it hard for the opponent to do likewise. The first international workshop on information hiding [2] brought these communities together and a number of hiding schemes were presented there; more have been presented elsewhere. We formed the view that useful progress in steganography and copyright marking might come from trying to attack all these first generation schemes. In the related field of cryptology, progress was iterative: cryptographic algorithms were proposed, attacks on them were found, more algorithms were proposed, and so on. Eventually, theory emerged: fast correlation attacks on stream ciphers and differential and linear attacks on block ciphers, now help us understand the strength of cryptographic algorithms in much more detail than before. Similarly, many cryptographic protocols were proposed and almost all the early candidates were broken, leading to concepts of protocol robustness and techniques for formal verification [6]. So in this paper, we first describe the copyright protection context in which most recent schemes have been developed; we then describe a selection of these ? The first author is grateful to Intel Corporation for financial support under the grant ‘Robustness of Information Hiding Systems’ ?? The third author is supported by a European Commission Marie-Curie grant David Aucsmith (Ed.): Information Hiding 1998, LNCS 1525, pp. 218–238, 1998. c © Springer-Verlag Berlin Heidelberg 1998 Attacks on Copyright Marking Systems 219 schemes and present a number of attacks, which break most of them. We finally make some remarks on the meaning of robustness in the context of steganography in general and copyright marking in particular. 1.1 Copyright Protection Issues Digital recording media offer many new possibilities but their uptake has been hindered by widespread fears among intellectual property owners such as Hollywood and the rock music industry that their livelihoods would be threatened if users could make unlimited perfect copies of videos, music and multimedia works. One of the first copy protection mechanisms for digital media was the serial copy management system (SCMS) introduced by Sony and Phillips for digital audio tapes in the eighties [31]. The idea was to allow consumers to make a digital audio tape of a CD they owned in order to use it (say) in their car, but not to make a tape of somebody else’s tape; thus copies would be limited to first generation only. The implementation was to include a Boolean marker in the header of each audio object. Unfortunately this failed because the hardware produced by some manufacturers did not enforce it. More recently the Digital Video Disk, also known as Digital Versatile Disk (DVD) consortium called for proposals for a copyright marking scheme to enforce serial copy management. The idea is that the DVD players sold to consumers will allow unlimited copying of home videos and time-shifted viewing of TV programmes, but cannot easily be abused for commercial piracy [19, 44]. The proposed implementation is that videos will be unmarked, or marked ‘never copy’, or ‘copy once only’; compliant players would not record a video marked ‘never copy’ and when recording one marked ‘copy once only’ would change its mark to ‘never copy’. Commercially sold videos would be marked ‘never copy’, while TV broadcasts and similar material would be marked ‘copy once only’ and home videos would be unmarked. Electronic copyright management schemes have also been proposed by European projects such as Imprimatur and CITED [45, 66, 67], and American projects such as the proposed by the Working Group on Intellectual Property Rights [69].