Information theoretic approach to the authentication of multimedia

In many multimedia applications, there is a need to authenticate a source that has been subjected to benign degradations in addition to potential tampering attacks. We develop one information-theoretic formulation of this problem, and identify and interpret the associated fundamental performance limits. A consequence of our results is that there is a tradeoff between embedding distortion and robustness to channel noise, but no such tradeoff between these parameters and security to forgery. To develop some intuition, we outline a sphere packing analogy and show that the results from sphere packing and information theory have the same form. One important benefit of our framework is a coherent way to analyze and design authentication schemes for general source models, distortion metrics, and noisy channel models. We illustrate this by an example construction of a realizable authentication scheme. An important ingredient of our construction is the use of forward error correcting codes. We show that the application of fairly simple codes decreases the embedding distortion required by more than 5 dB without decreasing security or robustness. Our approach is general enough to be used in a wide variety of applications.