Research On Novel Color Image Encryption Algorithms Based On 2D Hyperchaotic Systems

With the rapid development of information technology,a large number of digital images are generated on the Internet and spread through various networks every moment.Many of these images contain private or confidential information.Therefore,the image encryption,as the most intuitive and effective technology to protect image information,has been widely studied and used.The chaotic system is suitable for image encryption because of its many inherent characteristics such as initial state sensitivity and unpredictability.However,many existing image encryption algorithms have shortcomings in the chaotic systems used and encryption structures.For example,the simple structures of the chaotic systems lead to easy predication of their chaotic behaviors,and the designed encryption structures are only suitable for images with specific sizes.To overcome the shortcomings of existing image encryption algorithms,this thesis first constructed two two-dimensional chaotic systems,namely the 2D Logistic-TentModular map(2D-LTMM)and 2D Cosine-Logistic-Sine map(2D-CLSM),and then designed two new color image encryption algorithms based on these two chaotic systems,namely the LTMM-CIEA and CLSM-CIEA.The two constructed chaotic systems have a continuous and wide chaotic parameter range,and their outputs are uniformly distributed on the phase plane.At the same time,their two Lyapunov exponents and sample entropy are all greater than 0,and much greater than recently developed two-dimensional chaotic systems,2D-SLMM,2D-LASM,2D-LSCM and 2D-LSMCL.Therefore,these constructed two chaotic systems have hyperchaotic characteristics and higher complexity,and thus more suitable for image encryption application.The encryption algorithm LTMM-CIEA uses cross-plane permutation and nonsequential diffusion to obtain the confusion and diffusion properties.The cross-plane permutation can change the row and column positions of the pixels in the three color planes of a color image,while the non-sequential diffusion uses a random visit mechanism to change the value of pixels.Besides,some random noises are added during the encryption process and they can spread to all the pixels to achieve better encryption effect.The encryption speed of the LTMM-CIEA exceeds 16Mb/s,which is twice more than some similar algorithms such as the CMT-IEA and LSCM-IEA.Besides,the LTMM-CIEA has a high security level that can well resist many commonly used security attacks.The encryption algorithm CLSM-CIEA uses coordinate mapping permutation and plane-cross-plane diffusion to meet the confusion and diffusion properties.In the preprocessing stage,some random noises are also added.Then the algorithm uses 3D orthogonal Latin matrices to form a coordinate mapping that is used to change the pixel positions,and performs a diffusion operation using a plane crossing manner.Finally,a finite field multiplication operation is performed between the two encryption rounds to further improve the security level of the encrypted result.Security analysis shows that the CLSM-CIEA has high key sensitivity and can effectively resist the chosen-plaintext attack.Compared with some similar encryption algorithms such as the IES-JPFD and PWLCM-IEA,the adjacent pixel correlations of the CLSM-CIEA are closer to 0,its NPCRs and UACI values are closer to the optimal value,and its information entropy is closer to the maximum value 8.Therefore,the CLSM-CIEA also has a high security level.