Research On The Image Encryption Algorithm Based On The Chaotic System

With the rapid development of computer and network technologies, network security problem has attracted more and more attention. The digital images which have the features such as image, intuitive and vivid and so on, have become an important expression method of information transmission in the network. However, due to a large amount of data, redundancy and high correlation between pixels of the digital images and other characteristics, the traditional encryption algorithms such as DES, AES encryption algorithms are not suitable for image encryption. The chaotic system has the features such as sensitivity to initial conditions and control parameters, dense periodic points and topological transitivity which make it especially suitable for image encryption. In recent years, lots of image encryption algorithms based on chaos have been proposed. However most of the traditional encryption technologies are based on one-dimensional chaotic signal, owing to its small key space, safety and low defects, which make the encryption algorithm have a very big flaw. Based on this background, this paper put fractional order Chen system and high dimension chaotic system into image encryption algorithm, and it improve the security of the algorithm and complexity. The main work and innovation lies:1. First of all, the research developments at home and abroad as well as significance of the chaotic image encryption are analysed, and the basic knowledge of chaos and cryptography, and their relationships are given. Then the general steps and evaluation index of chaotic image encryption algorithm and the algorithm are introduced here.2. A new image encryption algorithm is proposed based on fractional order Chen system. The fractional order Chen system produces the scrambling sequence which is required firstly. Then the selection of the scrambling sequence of row and column is completed through the judgment of the plaintext message, which ensures that it is associated with the plaintext. After preprocessing the pixel values of the scrambling image by using the algorithm of grouping XOR, Two rounds of encryption are used in the pretreatment image, which increases the complexity and security of the algorithm. Finally the comparison with the integer order Chen system algorithm shows that the algorithm has a low correlation to the cipher text, larger key space and higher security. 3. Based on the characteristics of hyper-chaotic systems, a image encryption algorithm based on total shuffling scheme is put forward. Firstly, the required scrambling sequence is produced by using the hyper-chaotic systems to realize the scrambling of the pixel position. Then the scrambling sequence which is generated above is as the key of the Logistic map to get the encryption sequence, and it increases the coupling between the two processes. Moreover, to encrypt each pixel, this paper uses the sum of pixels which are located after and before encrypted that pixel, which ensures that it is associated with the plaintext and the cipher text, and it could effectively resistance against known/chosen-plaintext and different attacks. The theoretical analysis and experimental results indicate that the algorithm has a low correlation to the cipher text, larger key space and higher security.4. Based on digital images with large amount of data, high redundancy between adjacent pixels and other characteristics, in order to improve the security of the algorithm, a new image encryption algorithm based on sub-block is presented. Firstly, the four required scrambling sequence is produced by using the hyper-chaotic systems and the image is divided into four block with the same size at the same time, the selection of the scrambling sequence is completed by the judgment of the plaintext message, which realize the scrambling of image. Then the scrambling sequence and the plaintext, and the information before the encrypted cipher text and the corresponding block cipher text information are combined to generate cipher image, which increases the coupling between the two processes and ensure the correlation between neighboring pixels and sub-block, and it could effectively resistance against known/chosen-plaintext and different attacks. The theoretical analysis and experimental results indicate that the algorithm has a low correlation to the cipher text, larger key space and higher security.At last, the research work of the paper is summarized comprehensively, and the further research direction of the chaos-based image encryption is given.