On the combination of randomized thresholds and non-parametric boundaries to protect digital watermarks against sensitivity attacks

With unlimited access to a watermark detector, an attacker can use sensitivity attacks to remove the watermark of a digital medium. Randomized detectors and non-parametric decision boundaries are two ways of defending the watermark against these attacks. However, both approaches have their vulnerabilities when used individually. The first enables working with the randomized region boundary. The second still provides reliable information. This paper presents a combination of these two approaches to overcome their shortcomings. We develop a detector that has a randomized region with non-parametric outer boundaries. To empirically evaluate our combination, we apply two attack algorithms: Kalker's attack and Blind Newton Sensitivity Attack. The combination is more effective than the non-parametric boundary alone and comparable with using only the randomized threshold. In addition, we increase security by preventing attacks against the outer boundaries.