Research Of Correlative Techniques On Robustness And Encryption Of Digital Watermark

Digital watermark is the basic technology for authentication of digital works. In this paper, we perform researches on two aspects as robustness and encryption of watermark.On the research of robustness of watermark there are three aspects: first, we analyze the influence of low-pass filter to digital watermark. Two algorithms are used to embed and detect watermark respectively (they are watermark embedding with side information and correlation detection algorithm), through which, we examine the digital watermark robustness respectively with two types of filters, one is Gaussian low-pass filter and the other is Wiener low-pass filter. The experiment results prove that the influence lies in the frequency content of the reference pattern, in general, the inference of the reference module with high energy is larger than ones with low energy or void energy.Second, we put forward a robust authentication algorithm for binary image. Because of the simple binary nature of binary image, there is little discussion about it. An effective solution should take into consideration not only the security issue of reducing the possibility of being tampered with imperceptions but also the effectiveness of reducing the distortion resulting from authentication signal embedding.This paper attempts to use DCT (Discrete Cosine Transform) algorithm to realize the authentication of binary image. In order to improve the robustness of digital watermark and reduce image distortion, different intensity of watermark is embedded into the image according to its texture complexity. The experiment results show that the DCT algorithm is feasible to binary image. Compared with the spatial domain algorithm, the watermarked image by DCT almost has no distortion. At the same time, because having exacted robust character, it is robust to common signal distortions.At last, a spread spectrum watermarking algorithm in wavelet domain is introduced. Embed pseudorandom sequence which is modulated by watermark information into detail ponderance of cover image through spread spectrum technique. Furthermore, take HVS (Human Vision System) and the character of watermark image into account to ascertain the watermark embedding intensity and position. In addition, we use correlation detection algorithm to extract each bit of watermark information without cover image. The robustness of this algorithm is strong, moreover the embedded watermark is imperceptible.On the problem of encryption of watermark, we put forward a secure image transform scheme for digital image combining cryptography. In the scheme we design a new bi-layer watermark system including the watermark layer and the encryption layer. At the watermark layer, low-frequency information of the image is used to construct encrypting watermark taken advantage of md5 hash algorithm. At the encryption layer, the technology of digital envelope is used to ensure the security of transmission, In addition, we take advantage of chaos theory and HVS characteristic to improve the original watermark embedding algorithm. Conclusion from analysis and experiments shows that this scheme can predigest algorithm, prevent unauthorized detection and embedding, authenticate the authenticity and integrality of the image effectively.