A watermarking scheme in the encrypted domain for watermarking protocol

In most watermarking schemes for copyright protection, a seller always knows the embedded watermark identifying a buyer. However, it incurs both repudiation issue and framing issue. To solve these problems, many watermarking protocols have been proposed based on watermarking schemes in the encrypted domain. In this paper, we enhance an existing watermarking scheme and discuss public key cryptosystems used in watermarking protocols. Then, a new watermarking scheme in the encrypted domain with flexible watermarking capacity is proposed for watermarking protocol. It improves the robustness of watermarked image against JPEG compression after decryption and enables image tampering detection. The blind watermark extracting employs the same threshold criterion and secret keys as watermark embedding. Experimental results demonstrate that the enhanced scheme reduces computing overload and increases effective watermarking capacity, and that the proposed watermarking scheme in the encrypted domain outperforms a previous scheme.