Asymmetric schemes belong to second generation of watermarking. Whereas their need and advantage are well understood, many doubts have been raised about their robustness and security. Four di erent asymmetric schemes have been proposed up to now. Whereas they were seemingly relying on completely di erent concepts, they share the same performances. Exploring in detail these concepts, the authors propose a common formulation of the four di erent detector processes. This allows to stress common features about security of asymmetric schemes.
The unitarity property of transforms is useful in many applications (source compression, transmission, watermarking, to name a few). In many cases, when a transform is applied on real-valued data, it is very useful to obtain real-valued coefficients (i.e. a reality-preserving transform). In most applications, the decorrelation property of the transform is of importance and it would be very useful to control it under some transform's parameter (e.g. in joint source-channel coding). This paper focuses on fractional transforms, as tools for obtaining such properties. We propose a methodology for obtaining them and obtain variants of the Discrete Fractional Cosine (Sine) Transform which share real-valuedness as well as most of the properties required for a fractional transform matrix. As shown in [17], such matrices cannot be symmetric.
In the paper, we address oracle attacks for integrity watermarking in a communication setting. We show how an integrity verification algorithm can be modified in order to counteract an oracle attack. As an alternative to set up suitable communication protocols, we propose to counteract oracle attacks modifying integrity verification algorithms by adding a suitable temporal constraint.
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