The Research Of Image Encryption Algorithm Based On Chaotic System

Image encryption is a method to protect digital images by transforming images into unrecognized.The chaotic system is a kind of nonlinear systems with properties of ergodicity,initial value sensitivity and unpredictability which can be used in image encryption field.When chaotic systems are used to design encryption schemes,their performance highly determine the security levels of the encryption schemes.The thesis first introduces the definition and properties of chaos theory,and then designs a two-dimensional Logistic-Sine-coupled map(2D-LSCM)using two existing chaotic maps.The evaluation proves that 2D-LSCM has better performance than 2D Logistic maps in term of ergodicity,separation speed and chaotic range.The periodic analysis and NIST test show that 2D-LSCM can be used for image encryption,even chaos degradation exists when it is implemented.Using the designed 2D-LSCM,this thesis further proposes a Logistic-Sine-coupled map image encryption algorithm(LSCM-IEA).The algorithm adopts the classical confusiondiffusion structure.The permutation algorithm can scramble the image pixels of different rows and columns simultaneously,while the diffusion algorithm can spread microvariation to the whole encrypted result.The simulation results show that LSCM-IEA has faster encryption speed and lower time complexity than some newly developed image encryption algorithms.This thesis also analyzes the security performance of LSCM-IEA in terms of the key security,ability to resist differential attack,etc.The analysis results show that LSCM-IEA has better performance than several newest image encryption algorithms.Besides,to encrypt medical image with high precision,this thesis designs a bitplane-selective(BPS)image encryption algorithm which can selectively encrypt the images with any bit precision and has more application scenes.The designed BPS-IEA first preprocesses the image to select the encryption region,and then encrypts the image pixels in bit level.Thus,the proposed encryption algorithm can simultaneously change the pixel positions and pixel values.Meanwhile,the bit level diffusion is used in diffusion period.The simulation results show the good performance of the designed encryption algorithm.