Research And Application Of Chaotic Theory In Image Encryption

With the development of information technology, such as information·storage, information transmission and Internet, the security of information transmission has been heightened. As a main method of protecting image information, image encryption has made great strides in recent years. Chaos, the theory of relativity and quantum mechanics, are listed as the20th century’s greatest discoveries. It possesses the sensitive dependence on initial conditions and control parameters, pseudo random orbits and topological transitivity. These inherent properties can be well applied in the image encryption. So a large number of image encryption algorithms based on chaotic theory have emerged since the end of last century, and many exciting results are obtained. However, with the deep research and progress of information technology, the algorithms of image encryption which was once considered a strong safety and high efficiency, but now are proved to be unsafe, low efficiency and even unusable algorithms. How to base on the latest research results and to design a chaotic encryption algorithm for digital image with high efficiency and security by thorough analysis is becoming to the problem that will be solved urgently.This dissertation firstly introduces the basic knowledge of digital image encryption based on chaotic theory, combines with the results of digital image encryption based on chaotic theory, and deeply analyzes the current image encryption algorithms. The disadvantages of the algorithms are pointed out and improved. The original encryption algorithm for digital image is proposed in this dissertation, where the research work and the main innovations can be stated as follows:(1) In order to select the appropriate structure of chaotic image encryption for the different needs, the existing structures of chaotic image encryption are compared. Firstly, this dissertation analyzes the key steps used in encryption. The normal indicators are introduced in detail. Then, compared with the the existing structures of chaotic image encryption, we find the best structure for chaotic image encryption by experimental results. Finally, the antijamming capability of encryptional structures is analysed;(2) An algorithm of chaotic image encryption based on enhancing key is proposed. Compared with traditional algorithm, this algorithm possesses running effect and time without redundant operations. Compared with new algorithms, the proposed algorithm possesses better encrypting effect for different sizes and various test images. Finally, the antijamming capability of proposed algorithm is analysed; (3) An image encryption algorithm based on chaotic theory is cryptanalyzed and improved. According to the theory of cryptanalysis, the image encryption which is based on Logistic chaotic mapping and proposed by Ye is analyzed. This dissertation proves that the algorithm has a defect by solving differential equations, and designs an experiment to break it successfully. According to the defect, two improved algorithms are proposed;(4) In order to prevent maliciously tampering for the encrypted image, an image encryption and authentication algorithm based on reversible integer transform is proposed. Firstly, the plain-image is divied into low-frequency part and high-frequecy part. Then, the former is used to encrypt image by chaotic theory, and the latter is used to embed watermarking by histogram modification. The encrypted image with watermarking is obtained by inverse integer transform. The embedding rate and peak signal-to-noise ratio are better than previous works. Aiming at this problem that above algorithm can not effectively encrypt the outline information of plain-image, an improved algorithm is proposed to solve this problem. Finally, the antijamming and anti-attack capability of proposed watermarking algorithm are analysed;(5) A novel constraint condition for DNA coding is proposed, and used to design a chaotic image encryption based DNA coding. Compared with the existing constaint based on Hamming distance, the best combinational constraint for DNA coding is obtained by experimental results. Finally, the best constraint is employed to design chaotic image encryption based on DNA coding.Finally, the research work of this dissertation is summarized, and the future research direction is indicated.