Image Encryption Algorithm Based On Multiple Mixed Hash Functions

In recent years,the way of communication had changed greatly with the rapid development of computer and network technology.The multimedia communication has gradually become an important means for people to exchange information.Because of the openness and sharing of the network,it had caused a great potential of danger to the multimedia communication.Therefore,the security and confidentiality of the image are also becoming more and more important.Chaos has the characteristics of sensitivity to initial conditions,pseudo randomness,ergodicity and so on.Hence,chaos is closely connected with cryptography.Compared with the traditional encryption algorithm,the image encryption algorithms based on chaos theory are more advantageous in security,complexity,speed,etc.In recent years,it has gradually become a hot research subject.Based on the analysis of the defects of chaotic image encryption algorithms,some work has been made as follows:(1)A new one-time pad scheme for chaotic image encryption that is based on the multiple mixed hash functions and the cyclic-shift function is proposed.The initial value is generated using both information of the plaintext image and the chaotic sequences,which are calculated from the SHA1 and MD5 hash algorithms.The scrambling sequences are generated by the nonlinear equations and logistic map.This paper aims to improve the deficiencies of traditional Baptista algorithms and its improved algorithms.We employ the cyclic-shift function and piece-wise linear chaotic maps(Piece wise linear chaotic maps,PWLCM),which give each shift number the characteristics of chaos,to diffuse the image.Experimental results and security analysis show that the new scheme has better security and can resist common attacks.(2)A new chaotic image encryption scheme is proposed,which employs Josephus traversing and mixed chaotic map.The first process is a key stream generator based on the proposed mathematical model which is a chaotic system.The second process employs the Josephus traversing in scrambling;then the rows and columns of pixels are exchanged according to certain rules;therefore,we use chaotic coordinates to exchange the positions of each pixel.The third process employs the image data and four chaotic maps in order to modify the pixel gray-level values.The initial conditions for chaotic systems are derived using external secret keys by applying some algebraic transformations to the key.Security analysis indicates that the new scheme is effective.(3)A new chaotic image encryption is proposed,which is based on the coupled map lattices(Coupled map lattices,CML)and DNA diffusion sequences,and it's also a new one-time pad scheme.The initial values and control parameters of the CML system and logistics map are served as keys for one-time pad and calculated by utilizing the SHA-256 hash algorithm and the plaintext.In the pixel level,we utilize the CML system and sort function to encrypt according to the way from diffusion to scrambling;each pixel is encrypted by randomly DNA encoding,it means that a pixel consists of 4 bases in the DNA level;the Hamming distance and cyclic shift function are utilized to scramble,and the DNA encoding rules,the DNA complementary rules,the DNA operation rules and other operations are combined with the chaotic map for the diffusion process.The experimental analysis shows that the new algorithm has a large key space,it is sensitive to the key and plain images and the effect is better.