Based On The Quadratic Knapsack Encrypted Digital Watermark Technology

Currently, digital watermarking is an advanced technology in the international cryptogram research area. It protects the copyrights of digital productions by embedding some undiscovered infomation into the digital carrier. It provides a good solution to copyright protection and pirate copy tracing.In this paper, we propose a new digital watermarking algorithm based on quadratic knapsack problem, which belongs to public-key cryptosystem. The quadratic knapsack problem uses a matrix as public key to encrypt watermark information. It is hard to acquire private-key by calculating from public-key, and the speed of encryption is fast. We use quadratic knapsack problem to encrypt the watermark information and DCT(Discrete Cosine Transform) to complete the process of watermark embedding. In addition, for the sake of system robustness, the error-correcting code is added to improve the error-tolerated ability of encrypted information.The results of the experiments prove that the algorithm is robust to some commonly used image processing methods.