Study And Design Of Image Chaotic Encryption Algorithms

With the rapid development of the Internet and multimedia technology, more and more image information has been quickly and conveniently transmitted through the network, while the problem of the security and secrecy of image is becoming more and more important. Due to some intrinsic features of image, such as large data, high redundancy and so on, traditional cryptographic algorithms are not suitable for the protection of digital images. In recent years a variety of image encryption schemes have been proposed in accordance with the characteristics of digital image by many researchers, but they are not perfect enough. With the lucubrating of cryptography theory, many of encryption technologies have been attacked efficiently. And with the sale of digital image as electronic merchandising, researchers advanced a new image encryption model called degradation encryption which is a kind of process to reduce the visual effect of image voluntarily and reversibly. The degraded image is free for trial to every client, and then it would be decrypted or reconstructed if the client decides to pay. Therefore as the increasing applications to multimedia technology, to study image encryption is of profound theoretical and practical significance. Some contributions accomplished in this dissertation are as follows:Firstly, several common image encryption technologies and the image artificial degradation algorithm based on selective encryption are studied at great length. The potential flaws in these original algorithms are analyzed in detail, and then the corresponding improvement actions are put forward.Secondly, combining traditional encryption algorithms with chaotic cryptography, a novel feistel network image encryption algorithm is proposed based on chaotic map and dynamical S-box. Theoretical analyses and simulated experiment show that the proposed algorithm is very sensitive to initial condition and the diffusion and confusion properties of the algorithm are very idea1.The scheme can effectively resist differential analyses,statistic analyses and chosen plain image attack.Thirdly, the flaw in image degradation encryption based on entroy is improved effectively. And then a new image degradation encryption algorithm with reversible histogram spreading is projected. Finally the security of the deterioration model is analyzed carefully. Experiment results and analysis show that the algorithm can achieve image degradation and restoration rapidly, and have a good capability of resisting a variety of attacks.Fourthly, a new hash function construction algorithm based on image encryption scheme is put forward. The flaws in the tent map are analyzed in detail, and to overcome this problem a nonlinear piecewise map is constructed and introduced into the feistel network. Hash value with length of 128-bit is gained according to the rules. The one-way property, diffusion and confusion capability as well as collision resistance of the algorithm are studied by simulation. Theoretical analysis and computer simulations indicate that the proposed algorithm can satisfy the performance requirements of hash function.