Cryptanalysis And Improvement Of Chaotic Image Encryption Based On Permutation Diffusion Network

There are many essential connections between chaos theory and cryptography.In the past two decades,in order to design an effective encryption system for image data,the method of constructing encryption algorithm based on the chaotic system characteristics and Shannon's scrambling diffusion principle has been widely used in the field of image encryption.However,based on cryptanalysis research,a considerable part of image chaotic encryption mechanism has been proved to be unsafe.By analyzing the security of cryptosystem,the researchers put forward corresponding cracking schemes,which can further improve the encryption algorithm.This paper performs the cryptanalysis of three new image cryptosystems based on permutation and diffusion network.We demonstrate the security flaws about the three encryption algorithms.Then corresponding attack scheme are proposed,and the encrypted image is successfully cracked by the attack methods.Finally,an improvement image cryptosystem to remedy these security flaws is introduced.Furthermore,a series of experiments were carried out to evaluate the safety performance of the improved scheme.The main achievements of cryptanalysis and image encryption in this paper can be summarized as follows:(1)The Cryptanalysis of one-round permutation diffusion color image encryption related to plaintext proposed by Niyat et al is performed.Based on hybrid hyper-chaotic systems and cellular automata,the encryption algorithm constructs a pseudo-random generator,and then generates pseudo-random sequence to encrypt plaintext images.However,it was found that there are three security flaws in the algorithm after analysis,that is,diffusion effect in failure situation,small key space and XOR operation only used in diffusion process.The proposed attack method based on known plaintext attack and chosen plaintext attack effectively solves the equivalent key of the encryption scheme with decrypting the cipher image without the key.(2)Two typical image chaotic encryption mechanisms based on two-round permutation diffusion network are analyzed.By analyzing the two image cryptosystems based on Latin square proposed in 2015 and the improved algorithm using different keys in diffusion proposed in 2017.We summarize that the schemes have three same properties about diffusion,such as the cancelable of diffusion effect,etc.Based on these diffusion properties,the equivalent key sequence of four different keys used in two rounds of permutation and diffusion can be obtained by using the chosen plaintext attack method.(3)According to the above cryptanalysis work,the security problems of chaotic encryption schemes are summarized,and a chaotic image encryption mechanism with higher security is designed.Security experiments such as histogram analysis,correlation analysis,key space analysis,sensitivity analysis,information entropy analysis and robustness analysis are carried out to verify the security of the proposed image chaotic encryption mechanism.