Research On Image Encryption Algorithm Based On Chaos Theory

In the era of rapid development of information technology,hacker intrusion,network fraud and privacy leak occur frequently,so information security has become the focus of attention.Thus,protecting the security transmission of information has also become a hot topic of current research.Image,as the carrier of information,has the characteristics of vivid and large amount of information,and has become an indispensable part of people's communication.Based on the in-depth study of chaotic system theories and cryptography theories,three image encryption algorithms based on the chaos theories are designed in this thesis.The specific contents are as follows:First,an image encryption algorithm based on chaotic system theory and DNA sequence operations is proposed.The algorithm uses the SHA-3 algorithm to compute hash values of the plaintext image,and input keys as initial values of the 2D-LSCM chaotic system.Iterate chaotic system to obtain chaotic sequence.Through dynamic DNA coding of the image and the exclusive OR operations with the generated chaotic sequence,the scrambling of the pixels is realized,which further improves the security of encryption algorithm.Finally,the pre-set DNA coding rules are selected through DNA sequence operations to further enhance the confusion and diffusion characteristics of the algorithm.Second,an image encryption algorithm based on chaotic systems and genetic operations is proposed.The algorithm calculates the hash values of the plaintext image and the initial values of the chaotic map constructed by the given keys to establish the correlation between the plaintext and the keys,which makes the minor changes of the encrypted images spread to the whole cipher images,and uses the chaotic sequences generated by the chaotic maps to realize the image pixel position scrambling and the pixel value bit position scrambling;the crossover operations of the genetic algorithm are added to strengthen the diffusion of the pixel,and the security of encryption is further improved.Third,an image encryption algorithm based on the Hilbert curves and H-geometric fractals is proposed.The algorithm utilizes the space filling property of the Hilbert curve and the infinite property of the H-geometric fractal,and combines the pseudo-randomness of the hyperchaotic system and the sensitivity to initial values.The hash values of plaintext image are calculated by the SHA-3 algorithm as the initial values of the Logistic and Rossler chaotic systems,which make the keys associated with plaintext.The chaotic sequences generated by the chaotic systems are used to scramble the global pixel positions and the gray values of the image,disturbing the distribution of the pixel positions and the gray values of the pixel.The Hilbert curve and H fractal are used alternately to scramble the local pixel positions and diffuse the gray values of the pixel twice.Finally,the ciphertext feedback is used to further enhance the confusion and diffusion characteristics of the algorithm in order to achieve higher security.Finally,the contents of this thesis are summarized,and the future research directions are prospected.