Watermarking attack: security of WSS techniques

Most of watermarking techniques are based on Wide Spread Spectrum (WSS). Security of such schemes is studied here in adopting a cryptanalysis point of view. The security is proportional to the difficulty the opponent has to recover the secret parameters, which are, in WSS watermarking scheme, the private carriers. Both theoretical and practical points of view are investigated when several pieces of content are watermarked with the same secret key. The opponent's difficulty is measured by the amount of data necessary to estimate accurately the private carriers, and also by the complexity of the estimation algorithms. Actually, Blind Source Separation algorithms really help the opponent exploiting the information leakage to disclose the secret carriers. The article ends with experiments comparing blind attacks to these new hacks. The main goal of the article is to warn watermarkers that embedding hidden messages with the same secret key might is a dangerous security flaws