Research On Digital Image Encryption Algorithm Based On Chaos Theory And Ciphertext Diffusion

With the rapid development of science and technology,the Internet technology is-changing our lives every day,communication for information between people becomes more and more convenient.But,it also brings hidden trouble,in the transmission of information,important information has been stolen frequently,so encrypting the information becomes very important.This paper focuses on the topic of image encryption,the main work and research results are as follows:(1)This paper expounded the basic knowledge of cryptography,the basic theory of chaotic systems,typical image encryption algorithms,the means of attack crypto system and the index to measure the performance of cryptographic algorithms.(2)Improved an algorithm for image encryption based on bit replacement and ciphertext diffusion,the original algorithm formed by bit replacement process and XOR operation,and it can not meet the principle of diffusion for image encryption,and XOR operation can not resist the attack of chosen plaintext effectively,therefore on the basis of the original algorithm,added the diffusion encryption process and modulo operation for intermediate ciphertext image,the effect of changing a pixel value in the plaintext,spread to other pixel values in the ciphertext.Simulation and performance analysis show that the improved algorithm has larger key space,lower correlation between pixels and stronger ability to against differential attack than the original algorithm.(3)Proposed a color image encryption algorithm based multi-chaotic system,which using bit replacement and ciphertext diffusion.First,the color image is divided into three independent gray scale images,namely red(R),green(G)and blue(B)channel images,the bits of original gray image were replaced by sequence of chaotic system,then three encrypted images are interleaved with ciphertext diffusion,Then,the diffusion encryption method mentioned in the improved algorithm is used to encrypt each intermediate ciphertext image.When we get the three channel ciphertext image,The ciphertext image of each channel is merged to obtain the final ciphertext image.Through the simulation testing,The designed color image encryption algorithm has the advantages of large key space,strong key sensitivity,low correlation between the pixels of ciphertext images,and has strong ability to resist differential attack.(4)Proposed a color image encryption algorithm based on bit plane scrambling and ciphertext diffusion.After the color image is divided into three channel images,each channel image is decomposed by bit plane,and each channel image is divided into eight bit planes,the corresponding bit planes are merged according to the column,and eight merged planes are obtained,the eight merged planes are globally scrambled,and then decomposed into three parts:the front,the middle and the back.The twenty-four bit planes are exchanged and arranged sequentially,and the bit planes of the switching order are combined into three images.The three intermediate ciphertext images are grouped according to the pixel pairs,and the ciphertext diffusion operations are combined.Each encrypted image is encrypted and merged to obtain the final encrypted image.After simulation testing,the encryption algorithm of this chapter has the characteristics of the fast speed of encryption and decryption,high security and outstanding performance for resisting statistic analysis attack and differential attack.In this paper,an improved algorithm for image encryption based on diffusion is proposed,which has a good encryption effect,and on this basis,the two encryption algorithms for color image,proved by practice,has a good encryption effect.These algorithms have theoretical significance and practical value.