Security assessment of scalar costa scheme against known message attack in DCT-domain image watermarking

Security level analysis of watermarking techniques against intentional attacks receives more attention recently in watermarking theory. The most popular data hiding code using in digital watermarking is the scalar costa scheme (SCS). In this paper, SCS is implemented for digital image watermarking in Discrete Cosine Transform (DCT) domain. Then, Known Message Attack (KMA) is applied on SCS in order to estimate the secret key and evaluate practically the information theoretic security level of SCS. Empirical results show that practical security level of SCS is much lower than former theoretical result. Furthermore, it can be seen that the practical security level of SCS depends on the host statistics which has contradiction with the former theoretical result.