Tardos has proposed a randomized fingerprinting code that is provably secure against collusion attacks. We revisit his scheme and show that it has significantly better performance than suggested in the original paper. First, we introduce variables in place of Tardos' hard-coded constants and we allow for an independent choice of the desired false positive (FP) and false negative (FN) error rates. Following through Tardos' proofs with these modifications, we show that the code length can be reduced by more than a factor of two in typical content distribution applications where high FN rates can be tolerated. Second, we study the statistical properties of the code. Under some reasonable assumptions, the accusation sums can be regarded as Gaussian-distributed stochastic variables. In this approximation, the desired error rates are achieved by a code length twice shorter than in the first approach. Overall, typical FP and FN error rates may be achieved with a code length approximately five times shorter than in the original construction.

Unauthorized re-distribution remains a significant threat for emerging electronic movie distribution services. In this paper, we propose a forensic tracking watermark for MPEG-2 bit-streams that can be employed to complement Digital Rights Management and conditional access systems in electronic movie distribution. The watermark is embedded by modulating a subset of quantization matrix entries, which are periodically present in the MPEG-2 headers. When observed over time the watermark can be detected even after cropping, de-interlacing, resizing and DivX compression at 300 kbps or after being captured with a video camera from a flat-screen TV. As the method modifies only a small part of the bit-stream (ap100 bytes per second), it can be readily implemented in resource constrained environments like the current generation set-top boxes, without costly hardware upgrades.

In this paper, we propose an alternative DRM technology for next-generation optical media. Instead of implementing a hard access control mechanism, we propose a scheme that monitors the behavior of users in a privacy-preserving manner, detects potential infringement actions and reacts in a graceful way, which is dependent on the severity of infringements. The scheme is based on blacklists of known unauthorized content and compromised players, which are maintained by content providers and shipped alongside the content. Most of the functionality is implemented by content code provided on the disc, allowing for player independent and flexible reactions.