Cryptanalysis of optimal differential energy watermarking (DEW) and a modified robust scheme

This paper presents a cryptanalytic methodology of the well-known "Optimal Differential Energy Watermarking (DEW)" scheme. The DEW scheme divides the image into some disjoint regions (each region containing two subregions). In the DEW scheme, the watermark is a secret binary string where each individual bit information gets inserted in one of the regions by modifying the high-frequency Discrete Cosine Transform (DCT) coefficients. This modification creates a required energy difference between two subregions. We modify these high-frequency components so that this energy difference vanishes, and in turn, extraction of the watermark signal becomes impossible, making the cryptanalysis successful. Further, we improve the DEW scheme by inserting the watermark information in low-frequency components instead of high-frequency components and propose an oblivious. robust watermarking strategy that enables forensic tracking. We present statistical justification toward the robustness of our modified scheme.