Chaos And Its Applied Research In Image Encrytion

Image encryption technique consists of two parts,namely position permutation and grayscale substitution,in order to improve the security of image information,it hides the useful information of image.In recent years,some image encryption algorithms based on image's characteristic have been proposed,but the efficiency and security should be improved gradually.Chaos is produced by deterministic nonlinear systems,which has noise-like,broadband frequency spectrum,character,it is pseudorandom, reproducible phenomena,and chaotic system is extremely sensitive to initial condition,so chaos can be novel nature cryptosystem.If we make use of chaos in image encryption techniques,the image encryption algorithm will have a good efficiency and be safer.The image encryption technique based chaotic dynamics is focused in the thesis,mainly including generation of chaos and image encryption algorithm based chaotic dynamics.Firstly,the basic chaos theory and image encryption technique are briefly explained,and some familiar chaotic systems are discussed.And a method generating spread-spectrum sequences is advanced based on cross-feedback of chaos and CNN in the thesis.The simulation results indicate the chaotic sequences have ideal pseudonoise properties. Then,a image encryption scheme based on cross chaotic map is presented in the thesis.It can deal with the intractable problem of fast and highly secure image.The experimental results indicate that it is feasible.Finally,we propose a medical image encryption based chaos using symmetric cryptography.We make use of Cat map in position permutation,and we make use of Chen chaotic system for S-box design in the algorithm.The experimental results show the algorithm is safer, and it achieves adequate level of security for medical image transmission.