Study On Image Encryption Schemes Based On Hyper-chaos Systems

With the dramatic development of Internet,the transmission of images over Internet has become more and more popular.Meanwhile,the security of these images is under possible threat.Thanks to the natural relations between the chaos systems and the cryptosystems,many researchers pay attention to the study of chaos based image cryptosystems.Usually,hyper-chaotic system has more complex nonlinear dynamic behaviors than the normal chaotic systems.Hence,the hyper-chaos based image cryptosystems are usually considered to be more secure.In this dissertation,two hyper-chaos based image cryptosystems are proposed with detailed security analyses.An image encryption scheme based on a 2D hyper-chaotic system is designed.The pseudo random sequences generated by the 2D hyper-chaotic system are better in properties than those generated by normal chaotic systems.Different from the general chaos based image cryptosystem,the confusion and the diffusion procedures are interacted with each other.Thus the image encryption scheme has better performance and security.Upon the interacted structure,a new parallel image cryptosystem based on 5D hyper-chaotic system is proposed.A new parallel method is introduced to encrypt images in parallel,which promotes the efficiency of the image encryption scheme.Compared with the 2D hyper-chaotic system,the 5D hyper-chaotic system has more control parameters.Hence the key space of the corresponding image cryptosystem is larger,which makes it resist the brute-force attack better.Unlike the normal high-dimensional hyper-chaotic system,the 5D hyper-chaotic system is with cubic nonlinear product terms.Accordingly,it could resist some parametric identification technologies better.Compared with most high-dimensional hyper-chaotic based image cryptosystems,the proposed image encryption scheme based on 5D hyper-chaotic system improves the encryption speed in a parallel way.Security analyses and simulation results all demonstrate that this image encryption scheme gears the demand of digital image encryption acceptably.