Research On Application Algorithm Of Five-dimensional Hyperchaos In Image Encryption

Image information widely used in the media age,and image security issues is also worthy of attention.In many image encryption methods,many of the features of chaotic systems are suitable for image encryption such as sensitive initial condition and unpredictable.Logistic,Chen chaotic system all belong to the low dimensional systems,all of them control by small amount of initial value and small amount of system parameter iteration,Compared with low dimensional systems,high-dimensional mixed system have more initial values and parameters,all these can be seen as the secret key.And there are at least two positive Lyapnuov indexes,it also suggests that the dynamics system is more complex,multidimensional chaotic sequences contain each other,increase the difficulty of breakers' work.This thesis first introduces the chaos theory and the Lorenz system ethnic group,mainly introduces the five dimension Lorenz hyperchaotic system used in the paper.Secondly,two new pretreatment methods are proposed,which are double "sort transformation" and "improved chaotic diffusion encryption".The later one solve the drawback that all images can be decrypted by just two original map and corresponding secret map without using the key when use traditional diffusion encryption method.Thirdly,three kinds of encryption algorithms are proposed,the first method is the image encryption algorithm based on digital signature.This method uses MD5 value to control the initial value of the sequence,which makes the key contact with the plaintext closely,gets rid of that all images are encrypted with the same sequence,improves the sensitivity of the algorithm to plaintext and resists differential attack efficiently.The second method is image encryption algorithm based on hyperchaos and improved AES.This method uses chaotic sequence to replace the original add round key,which prevents the translator from getting all the secret keys.The translator usually get all secret keys and a round of secret key through public key expansion algorithm.The third method is the image frequency domain hiding algorithm based on hyperchaos.This method,which uses the characteristic of high frequency component's storage is small,hides the original image in the high frequency component of the medium image,so that the resulting encrypted image is a clear media image,which sets obstacles for the interpreter.Finally,the Matlab simulation results show that,the three methods proposed in this thesis can effectively deal with image encryption and decryption issues,the encryption scrambling effect is good,the degree of reduction is high after the decryption and at the same time has a certain anti-attack capability.