Security analysis of a self-embedding fragile image watermark scheme
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Recently, a self-embedding fragile watermark scheme based on reference-bits interleaving and adaptive selection of embedding mode is proposed. Reference bits are derived from the scrambled MSB bits of a cover image, and then are combined with authentication bits to form the watermark bits for LSB embedding. We find this scheme has a feature of block independence of embedding watermark such that it is vulnerable to a collage attack. In addition, because the generation of authentication bits via hash function operations is not related to secret keys, we can apply a multiple stego-image attack on this scheme and the cost of acquiring all the permutation relations (i.e., equivalent permutation keys) of l· b^2 watermark bits of all blocks is about (l· b^2)! for the embedding mode (m, l), where m MSB layers of a cover image are used for generating reference bits and l LSB layers for embedding watermark, and b× b is the size of image block. The simulation results and the statistical results demonstrate our analysis is effective.
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