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Generation of embedding watermark signals from reference watermark of the detector

In this paper, we study asymmetric watermarking schemes which use different keys for the embedder and the detector. In an additive asymmetric marking system, the reference watermark of the detector and the embedded watermark in the host signals should be different but have some correlation value above a threshold if the detector does a correlation test. Watermark signals can be decomposed into the magnitude and the phase components in the frequency domain. It is shown that the latter plays a more critical role in the correlation detector than the former does. It motivates us to propose a method to generate a set of embedding signals by randomly shifting the phase of the reference watermark. We also analyze the security of our method when the reference watermark is open to the attackers.