Research On Image Encryption Algorithm Based On Chaotic System

Image representation information is intuitive,and it is often used as a medium for people to obtain information.Nowadays,network has developed rapidly and people obtain images through the Internet quickly.The network is an open platform which causes images to be easily stolen and maliciously attacked during network transmission.Therefore,it is important to transfer the images securely.Images have many features such as large data flow,high redundancy,and strong correlation.However,common encryption algorithms such as DES and AES can't meet the requirements for images transmission safely.Chaotic systems have characteristics such as ergodicity,pseudo-randomness,aperiodicity,and high sensitivity to initial conditions,which can realise image transmission security.Therefore,this paper mainly studies the encryption of images based on chaotic systems.1.The encryption algorithm is designed based on Gray code,chaotic system and secure hash algorithm(SHA-384).Because some existing pixel-level encryption algorithms can't provide good protection against plaintext attacks and low encryption.It includes three phases,image preprocessing,scrambling and diffusion.SHA-384 is used to generate the key.In the preprocessing phase,firstly,the encryption algorithm decomposes the color image into three components of R,G,B;Secondly,the three components are scrambled as a whole according to the one-dimensional chaotic sequence.In the scrambling phase,the encryption algorithm uses the Gray code transformation to complete the global scrambling,and it performs scrambling transformation between the rows and columns according to the chaotic sequence.During the diffusion phase,the encryption algorithm uses forward and reverse XOR operations.Experiment shows that the algorithm can resist attack of the difference,select the plaintext and so on,and this algorithm has good encryption effect.2.The DNA encryption algorithm is designed based on hyperchaotic system,secure hash algorithm(SHA-384)and group encryption structure.Because some existing encryption algorithms based on DNA encoding,there is a large amount of computation,low security and can't resist plaintext attacks.The SHA-384 algorithm is also used to generate the keys.Firstly,the encryption algorithm performs preprocessing of the whole color image components.Secondly,according to the DNA encoding rules,the three preprocessed components are encoded to obtain three DNA planes,and the positions of elements in the three DNA planes are disturbed by the hyper-chaotic sequence through row and column cross-swap operations.Finally,the three-scrambling DNA planes are grouped and diffused using a DNA-based grouping structure,and the algorithm performs DNA decoding on the diffused DNA planes to obtain an encrypted image.Experiments show that the encryption algorithm reduces the correlation between pixels,at the same time,it also increases the space of the key,so that the security of ciphertext is guaranteed.3.The S-box block encryption algorithm is designed based on chaotic system and secure hash algorithm(SHA-512).Because some existing S-box encryption algorithms,the use of fixed single and defective S-boxes to replace the ciphertext is not safe enough.The key is generated by SHA-512.In this encryption algorithm,color image components are preprocessed,then scrambling and diffusion are performed.In the scrambling phase,the encryption algorithm performs left and right two-dimensional mapping for the three preprocessed components to change the position of the pixel,and the number of mappings is generated by the key.In the diffusion phase,the three scrambled components are grouped according to the chaotic sequence;then different S-boxes are constructed by the chaotic system;finally,the gray value of each image group is replaced according to different S-boxes.Experiments show that the algorithm not only has better key sensitivity,but also resists various attacks.