Research On Digital Image Encryption Algorithm Based On Chaos Theory

In recent years,the Internet industry has boomed.As one of the most useful forms of information representation,images are widely used in various fields.The leakage of image information may cause property damage and adverse social impact,so the protection of image information is of great significance.Because the traditional text information encryption algorithm is not designed specifically for the image,it is no longer applicable in image encryption.Chaotic system is unpredictable,extremely sensitive to the initial value,the generated sequence exhibits pseudo-randomness and so on,combined with chaotic system design of image encryption algorithm can effectively solve the problem of image information leakage,in order to solve the problems that the existing chaos-based image encryption algorithms have low encryption efficiency and cannot resist chosen-plaintext attack and noise attack,and the poor practicability.The following research work has been carried out in this thesis:Firstly,based on cryptography and the permutation-diffusion architecture of chaotic-based image encryption algorithm,two chaos-based image encryption algorithms are studied respectively in Electronic Code Book mode and Cipher Block Chaining mode.By comparing with the data encryption standard in two different modes,it is concluded that the traditional cryptographic techniques is not suitable for image encryption,and the advantages and disadvantages of the typical chaotic-based image encryption algorithm in the two common modes are also summarized as well as the problems existing in the algorithm of image encryption,these provide research direction and improved space for the design of the chaotic-based image encryption algorithm.Secondly,at present,based on the typical permutation-diffusion encryption algorithm encryption has low efficiency,operation cannot be executed in parallel,encryption cannot resist chosen-plaintext attack and other issues,A fast image encryption algorithm based on hyper-chaotic system and one-way coupled map lattices(OCML)is proposed.The use of innovative scrambling and diffusion operation,so the algorithm can run in a serial and parallel coexistence computer environment.In the permutation stage,the position of image pixels is disturbed by the combination of Baker mapping and chaotic scrambling.Compared with the simple Baker mapping transformation,the scrambling periodicity is overcome.At the same time,each scrambling can be processed in parallel,which improves the scrambling efficiency.In the diffusion stage,the diffusion processing between the pixels of each image block is first carried out by using one-way coupled map lattices with two local mappings and hyper-chaotic system.Then the image is flipped and block.In the end,each block is diffused separately,in which the diffusion of each block can be processed in parallel.Experimental results and comparison with relevant research results show that:the algorithm can achieve high security without multiple rounds of repeated execution,and the encryption efficiency is improved significantly.At the same time,random numbers and ciphertext feedback are introduced to enable the algorithm to resist all kinds of common attacks.Finally,the algorithm combining compressed sensing and chaos-based image encryption has many advantages,however,a lot of chaos-based image encryption algorithms based on compressed sensing have some problems such as large size of measurement matrix,poor physical implementation,and inability to resist chosen-plaintext attack,to solve these problems,an chaos-based image encryption algorithm based on fast compressed sensing is proposed.Firstly,the initial values and parameters of chaotic system are generated by using the SHA-256 hash value of image;the chaotic pseudo-random sequence generated by the chaotic system is then used to generate a scrambled block Hadamard ensemble matrix;and finally use the SBHE as the measurement matrix of compressed sensing to compress and sample the image.In addition to the compression measurement,the image quantization,scrambled and block pixel value replacement processing is carried out after compression and encryption.Experimental results show that the proposed algorithm not only has the performance of compression,but also has high encryption security,which can resist many kinds of attacks.In summary,the results show that the two chaos-based image encryption algorithms proposed in this thesis have better encryption performance,and thealgorithm has high theoretical value and wide application prospects.