Analysis and Improving the Security of the Scalar Costa Scheme against Known Message Attack

The popular watermarking method with structured codebook is the Scalar Costa Scheme (SCS) which is highly robust but poorly secure. Known Message Attack (KMA) is a type of the security attacks which its countermeasure is more difficult than others. This paper proposes a novel scheme to increase security of SCS in KMA scenario. For this purpose, the SCS model is extended to a more general model. The security of Generalized SCS (GSCS) is analyzed using residual entropy as a security measure. Then, fundamental trade-off between security and achievable rate of GSCS is proved in KMA scenario. Based on this trade-off and the practical security attack on SCS, a new extension of SCS is proposed, called Surjective-SCS (SSCS). In comparison with SCS, SSCS clearly achieves more security and achievable rate in low Watermark to Noise Ratio (WNR) regime.