Better security levels for "Broken Arrows"
Résumé
This paper deals with the security of the robust zero-bit watermarking technique Broken Arrows (BA),1 which was invented and tested for the international challenge BOWS-2.2 The results of the first episode of the challenge showed that BA is very robust and we proposed last year an enhancement called Averaging Wavelet coefficients (AWC),3 which further strengthens the robustness against the worst attack disclosed during this BOWS-2s first episode.4 However, in the second and third episodes of the challenge, during which the pirates could observe plenty of pictures watermarked with the same secret key, security flaws have been revealed and discussed.5 Here we propose counterattacks to these security flaws, investigating BA and its variant AWC. We propose two counterattack directions: to use the embedding technique AWC instead of BA, and to regulate the system parameters to lighten the watermarking embedding footprint. We also discuss these directions in the context of traitor tracing.6 Experimental results show that following these recommendations is sufficient tocounter these attacks.