Digital Watermarking Based On Public Key Cryptosystem And DWT

With the wide application of digital media technology and information technology, illegal users can copy other people’s products cheaply and conveniently. This behavior harms the copyright proprietors’right, and to protect the copyright of digital products becomes a problem urged to be solved. As a burgeoning technology which can effectively protect the copyright of digital products, digital watermarking technology is attached much importance and researchers have gained some achievements. After understanding the related algorithm in detail, the author proposed the new color image robustness blind watermarking algorithm. In order to solve more effectively the problem that digital products purchasers upload their products on the internet for other people to copy, the author also proposed the color image digital watermarking algorithm which combines digital signature. This algorithm also adopts chaotic algorithm, error correction coding, HVS, promoting wavelet transform, and a new blind watermarking embedding algorithm to improve the robustness and security of the watermarking. The main works are as follows:(1) The color image blind watermarking algorithm is designed, which is based on error correction coding, chaotic sequence, spread spectrum technology, HVS, and promoting wavelet transform. Firstly, before embedding the watermarking, do the following things to the two-value watermarking image: spread spectrum, Logistic chaotic mapping, error correction coding pretreatment, so as to improve the robustness and security of this algorithm. Secondly, as the Frequency-domain characterization of HVS shows, human being’s eyes have low sensibility to the high frequency information, which means the sensibility of human being’s eyes to the texture close quarter is lower than to the smooth quarter and the sensibility to blue is lower than to red and green. Therefore, it is necessary to extract the B component in the original color image to promote wavelet transform at three levels, and to use different watermarking embedding methods at low and medium frequency part. Thirdly, it is to prove the invisibility, validity, security and robustness of this algorithm by large number of data and experiments. The final step is to illustrate the advantages and disadvantages of this algorithm by comparing with other algorithms.(2) Based on the algorithm above, the author proposed the digital watermarking algorithm using digital signature. This algorithm adds digital signature and encryption in the procedure of watermarking pretreatment, which makes it possible not only to authenticate the purchaser’s identity but also to ascertain the copyright owner’s copyright in the procedure of extracting the watermarking. So if the copyright owner finds that the purchaser uploads the digital products on the internet for other people to copy, he can obtain evidence in the supervisory board and investigate the purchaser’s related legal liability through legal effect. The algorithm requires a high watermark robustness. In order to improve its robustness, the error correction coding is used in the procedure of watermarking pretreatment. In the process of embedding the watermarking, after the watermarking invisibility is achieved under certain condition, more attention is paid to improve the robustness of this algorithm.