On Reliability and Security of Randomized Detectors Against Sensitivity Analysis Attacks

Despite their popularity, spread spectrum schemes are vulnerable against sensitivity analysis attacks on standard deterministic watermark detectors. A possible defense is to use a randomized watermark detector. While randomization sacrifices some detection performance, it might be expected to improve detector security to some extent. This paper presents a framework to design randomized detectors with exponentially large randomization space and controllable loss in detection reliability. We also devise a general procedure to attack such detectors by reducing them into equivalent deterministic detectors. We conclude that, contrary to prior belief, randomization of the detector is not the ultimate answer for providing security against sensitivity analysis attacks in spread spectrum systems. Instead, the randomized detector inherits the weaknesses of the equivalent deterministic detector.