Cryptanalysis of an improved fragile watermarking scheme

International audience; This paper presents two attacks on Teng et al.'s fragile watermarking algorithm. Both attacksallow the attacker to apply valid watermarks on tampered images, therefore rendering thewatermarking scheme useless. The first attack uses the watermarked version of two chosenimages, and the second attack, a generalization of the first, uses a number of arbitrarywatermarked images. The paper also models the cryptanalysis process for the second attackusing Markov chains in order to demonstrate that the necessary number of images is relativelysmall for a high probability of successful attack. All the results that are presented in thispaper have been confirmed by a practical implementation.