Attacking digital watermarks

This paper discusses inherent vulnerabilities of digital watermarking that affect its mainstream purpose of rights protection. We ask: how resistant is watermarking to un-informed attacks ? There are a multitude of application scenarios for watermarking and, with the advent of modern content distribution networks and the associated rights assessment issues, it has recently become a topic of increasing interest. But how well is watermarking suited for this main purpose of rights protection ? Existing watermarking techniques are vulnerable to attacks threatening their overall viability. Most of these attacks have the final goal of removing the watermarking information while preserving the actual value of the watermarked Work. In this paper we identify an inherent trade-off between two important properties of watermarking algorithms: being "convincing enough" in court while at the same time surviving a set of attacks, for a broad class of watermarking algorithms. We show that there exist inherent limitations in protecting rights over digital Works. In the attempt to become as convincing as possible (e.g. in a court of law, low rate of false positives), watermarking applications become more fragile to attacks aimed at removing the watermark while preserving the value of the Work. They are thus necessarily characterized by a significant (e.g. in some cases 35%+) non-zero probability of being successfully attacked without any knowledge about their algorithmic details. We quantify this vulnerability for a class of algorithms and show how a minimizing "sweet spot" can be found. We then derive a set of recommendations for watermarking algorithm design.