Research And Application Of Digital Image Encryption Technology Based On Chaotic Maps

Digital image is becoming the main image format for its convenient storage and high transfer speed, and is used in many cases such as personal digital photos, medical image transfers, military image transfers etc. However, since the network is an openning, complex and changeful environment, digital image faces many threats. As a result, more and more researchers have devoted their attentions to the digital image encryption algorithm with higher security. Digital image encryption algorithm based on chaotic maps has inherited many characters of chaotic maps. They have numerous keys and maintain sensitivity to initial key. Digital image encryption algorithm based on various chaotic maps provides security protection for image storage and transfers in many crucial application fields.Based on the theory of chaotic system and digital image encryption techonlogy, the thesis has analyzed the security of two chaos-based image encryption algorithms, and has reseached two chaos-based image encryption algorithms, together with their relevant application scheme.The major contributions are described as follows.(1) The security of two chaos-based image encryption algorithms under known image attack is analysed. We point out the ability of resisting known image attack can not improve well by just changing pixels position. The weakness of chaotic maps and the inconsequence of key generation algorithm also make the ability of algorithm resisting known image attack down.(2) A chaos-based color image encryption algorithm and a chaos-based gray image encryption algrithm are designed. In the former, pixel value replacement based on Logistic map is added to improve the ability of resisting known image attack. It performs easily and encrypts at high speed, and is very suitable for securing the color image containing many pixels. The latter combining 3D Lorenz map and 3D Cat map, encrypts and decrypts image with the aid of proper Perturbance in the system. It gives up some efficiency to improve security, so it is more suitable for securing the gray image containing lesser pixels. The analysis and simulation results show that above two algorithms can resist known/chosen image attack.(3) The application schemes of above two chaos-based encryption algorithms are given. In the embedded application, an embedded encryption system for the former algorithm is proposed. Simulation models of encryption and decryption modules are designed using Matlab/Simulink, and the flow of how to integrate the modules into the embedded system is described. In the watermark image application scheme, based on the existing digital right protection system, its watermark image preprocessing module is improved The basic model and work flow of the watermark image preprocessing system are proposed, and are designed and implemented using Matlab/GUI.