Research On Chaos Based Information Encryption And ImageWatermarking Algorithms

The fast development and all-pervading application of computer network technology and digital multimedia technique, make the protection of multimedia content become a crucial issue in information security. In consideration of the deficiency of traditional cryptology, recently people are seeking more effective approaches to fulfill the requirements of multimedia protection, among which chaos based encryption and digital watermarking technology exhibit prospective superiority,which may become new valid means of multimedia content protection.In this dissertation, several chaos based information encryption schemes and image watermarking algorithms are studied, which are detailed as follows:(1) Basic theory of chaos and relationship between cryptological transformation and chaotic map is investigated. A discrete chaotic cryptography algorithm based on combined external key and plaintext is proposed, the algorithm improves the chiptext sensitivity with plaintext and secret key and the distributing characteristics of ciphertext. A fast combined chaotic cryptographic method fit mobile computing is proposed, it has the superiorities of robustness against system recognition attacks, high speed, little resource consuming.Two image encryption algorithm based on high dimensional nonlinear chaotic system is proposed, include an algorithm of chaotic images scrambling based on two chaotic sequences sort transformation which improves the scrambling performance.These algorithms can enhance encryption security.(2) The technique of image copyright protection is studied. We proposed a novel binary image digital watermarking algorithm based on DWT and chaotic scrambling, concept of majority and minority watermark bit is introduced, and the idea of dissymmetrical quantization method in watermarks embedding is proposed.The algorithm enhances security and improves invisibility of watermarks.We proposed a novel spatial domain digital watermarking algorithm based on chaotic map, the space positions and bit positions for watermarks embedding can be selected randomly, and the strategy of minimizing changes of host image pixels is adopted, the algorithm enhances security and robustness or invisibility of watermarks. We also proposed a novel image digital watermarking algorithm combining DWT and sptial domain, the watermark image is splitted into two parts according to the data importance, it provides more watermarks and minimizeds the distortion of the watermarked image.(3) The technique of fragile watermarking for image content authentication is studied. We propose a sensitive chaotic fragile watermarking algorithm for binary images verification, in which the concept of Least Significant Pixel Block (LSPB) is introduced. The fragile watermark that is generated by the binary sub-image content and chaotic map is embedded into the middle pixel of the LSPB. The algorithm has good invisibility and high sensitivity to tampers on binary image local content.We also proposed a chaotic semi-fragile image watermarking based on block-DCT,by using speciality of block-DCT and chaotic map, it enhances the robustness against mild attacks such as JPEG compression and other image processing and fragility to image local content tamper attacks.(4) The dual watermarking technique for image copyright protection and content authentication simultaneously is studied. We proposed dual watermarking algorithms based on image DWT and block-DCT, respectively. A new dual-parameter unsymmetrical quantization method for significative binary watermarks embedding is proposed, which reduces the impact on cover image visual quality. The robust watermarks are embedded into the sense important coefficients of transform domain, so that the robustness is enhanced.While the fragile watermarks are embedded into sense nonsignificant coefficients of transform domain, so that the semi-fragility is enhanced. The algorithm has good security and low computational complexity.(5) The multipurpose watermarking techenique is studied. We proposed a security multipurpose image watermarking system model and algorithm, in which the watermarks embedding intensity and embedding positions are all controlled by high dimension nonlinear chaotic system, the watermarking system has the security of cryptography. It can not only validate the image copyright, but also track the action of unauthoritatively image copy. By utilizing the dual-parameter unsymmetrical quantization method, the cover image visual quality or watermarks robustness is enhanced. By using lift wavelet transformation, the computational speed is accelerated and the memory cost is reduced.Finally, the thesis is concluded by pointing out some open issues on the research of chaos based encryption and digital watermarking as well as highlight some further research directions.