Research Of Medical Image Encryption Algorithm Based On Chaos

As an important information carrier,the security of digital image has been paid more and more attention,and the research of image encryption algorithm has become a hotspot.As a special image form,the medical image contains patients’s privacy information such that it is more important to protect the security of the medical image.Because of the sensitivity of the initial conditions and the paramters for chaotic systems,and pseudo-random chaotic orbits,it is of great practical significance to study image encryption schemes based on chaos,especially the medical images.This thesis focuses on the security of medical image encryption algorithm.We analyse the security of a medical image encryption proposed by Hua’s et al.,point out the security hidden dangers of the algorithm,and proposes an improved scheme for the existing loopholes;designs an image encryption algorithm based on dynamic diffusion and dimensional transformation permutation.The main research work of this thesis is as follows:First,the security of a medical image encryption using high-speed scrambling and pixel adaptive diffusion is analyzed.In this thesis,the security of the algorithm is analyzed via differential cryptanalysis and chosen ciphertext attack in detail.The decryption process is analyzed theoretically by differential cryptanalysis and linear relationship is constructed between plain-images and cipher-images.Based on the linear relationship,a codebook is established,and the codebook attack breaks Hua et al’s algorithm.The size of the codebook is determined by the size of the cipher-image.If the size of the cipher-image is M x N,the constructed codebook contains(M × N + 1)pairs of plain-image/cipher-image.The experimental results verify the theoretical analysis.To improve the security of Hua et al’s algorithm and to resist the differential cryptanalysis,an improved scheme is proposed.In the improved scheme,plaintext-related permutation matrices are introduced.The simulation and statistical results show that the improved scheme not only inherits the advantages of the original algorithm,but also resist the differential cryptanalysis and the codebook attack.Second,considering the characteristics of medical images,this thesis proposes a medical image encryption scheme based on dynamic diffusion and dimensional transformation permutation.Dynamic diffusion can scramble the pixels in image blocks into different rows and columns,which not only weakens the strong correlation between adjacent pixels,but also has different mapping relationships among pixel positions of different images.Dimensional transformation confusion makes the algorithm non-linear.The experimental results show that the scheme can encrypt different types of digital images into random images,and the security evaluation shows that the scheme has better security.