Digital Image Encryption Based On Chaotic Systems

With the rapid development of the digital age,digital image has become an important form of expression in contemporary media and has been widely used in production and life.However,at the same time,the security of digital image data is also facing more and more severe challenges.Therefore,image encryption has gradually become a research hotspot in information security.Chaotic mapping is widely used in the process of cryptographic scrambling and diffusion because of its excellent characteristics.Compared with traditional image encryption technology,chaotic digital image encryption has more advantages in key space,algorithm efficiency and security performance,and has become one of the most widely used digital image encryption methods.As new theoretical image encryption schemes have been proposed,chaotic image encryption has been more closely integrated with other theoretical disciplines.These encryption schemes generally combine chaotic mapping with other theories to improve algorithm performance.In order to solve the problem of strong correlation between three components of chaotic color image encryption,two chaotic digital image encryption algorithms are proposed by combining chaotic system and DNA sequence operation.Specific work contents are as follows:(1)Based on the excellent characteristics of chaotic system and DNA sequence operation,an image encryption algorithm combining chaotic mapping and DNA sequence operation is studied.The algorithm adopts the scramble-diffusion architecture.In the scrambling process,a variable step size block scrambling method is proposed by combining sawtooth obfuscation and Joseph ring,which reduces the correlation between adjacent pixels.In the diffusion process,the scrambled red,green and blue components and chaotic sequence matrix are first converted into DNA matrix,and the three-component matrix is xor in pairs to solve the strong correlation problem among the three components.Then the DNA matrix of the pseudo-random sequence is used to spread the DNA matrix of the three components twice,so that the three components of the ciphertext image contain chaotic sequences.This algorithm combines chaotic system with hash function(SHA-256),making DNA encoding and chaotic sequence generation depend on plaintext information.Therefore,the algorithm is highly sensitive to plaintext images.Experimental results show that the correlation coefficient between adjacent pixels of ciphertext image is close to 0,and the algorithm adopts 512×512×3 Lena color image for test and comparison,and the information entropy reaches 7.9997.Both experimental results and security analysis show that the algorithm has good encryption effect and reliable security performance.(2)Due to the discreteness of cellular automata in space,time and state,a digital image encryption algorithm based on location index of elementary cellular automata(ECA)blocks and double chaotic mapping is studied.Firstly,the three components of the digital image are separated,and the three components are grouped into a large matrix from left to right.Then,a block replacement mechanism based on the position index value of cellular automata is introduced to dynamically exchange the pixel blocks of three components to effectively reduce the correlation between the three components.A new pixel scrambling method is proposed which uses Joseph scrambling to achieve pixel value confusion and pixel value diffusion.Finally,random sequences are introduced to carry out DNA computation on the three components.Compared with the diffusion method based on pixel level,DNA diffusion is better in terms of diffusion effect and encryption efficiency.Because the algorithm uses the secure hash algorithm(SHA-512)to generate the initial values and parameters of the chaotic system,the algorithm is very sensitive to the plaintext image.The simulation results show that the image encryption algorithm based on the location index of elementary cellular automata blocks has good confusion and diffusion characteristics,and can effectively improve the encryption effect.The experiment verifies a number of different color images of different sizes.The experimental analysis shows that the algorithm has high security in histogram,entropy,correlation of adjacent pixels and a large number of security analysis shows that the algorithm can effectively resist various attacks.