Design of secure watermarking scheme for watermarking protocol

Watermarking technique enables to hide an imperceptible watermark into a multimedia content for copyright protection. However, in most conventional watermarking schemes, the watermark is embedded solely by the seller, and both the seller and the buyer know the watermarked copy, which causes unsettled dispute at the phase of arbitration. To solve this problem, many watermarking protocols have been proposed using watermarking scheme in the encrypted domain. In this paper, we firstly discuss many security aspects in the encrypted domain, and then propose a new method of homomorphism conversion for probabilistic public key cryptosystem with homomorphic property. Based on our previous work, a new secure watermarking scheme for watermarking protocol is presented using a new embedding strategy in the encrypted domain. We employ an El Gamal variant cryptosystem with additive homomorphic property to reduce the computing overload of watermark embedding in the encrypted domain, and RA code to improve the robustness of the watermarked image against many moderate attacks after decryption. Security analysis and experiment demonstrate that the secure watermarking scheme is more suitable for implementing the existing watermarking protocols.