Study On Digital Image Encryption Based On High-Dimensional Hyper-Chaotic System

The security of image regarded as an important information carrier is widely concerned by people.The most effective way to protect the confidentiality of images is encryption.Owing to some characteristics of images including large data capacity,high redundancy and correlation between adjacent pixels,causing conventional textual encryption to be proved unsuitable for image encryption.Chaotic systems have remarkable properties such as ergodicity,pseudo-randomness and high sensitivity.It has a natural connection with cryptography and can be widely used in image encryption.Two image encryption algorithms based on high-dimensional hyper-chaotic system are proposed in this paper.The specific research work is as follows:A dynamic diffusion image encryption scheme based on hyper-chaotic system and SHA-256 functions is proposed.The initial values of the state variables of hyper-chaotic systems are generated by the SHA-256 hash values of the images,which can resist the chosen-plaintext attacks.In the scrambling stage,the chaotic sequences are ascending to get an index sequence,and then the pixels are changed without repetition.The encryption of the current pixel relies on the encrypted pixel depending on the chaotic sequence rather than traditional linear rule in the diffusion phase,thereby breaking the fixed order in the diffusion process.A color image encryption algorithm based on six-dimensional hyper-chaotic system and bit plane is designed.The initial state values of the six-dimensional hyper-chaotic system contain some information of the plaintext image,which can resist the chosen-plaintext attacks.In the scrambling stage,for the characteristics of the bit plane of the image,the bit planes of the color image are reordered and combined to generate a new two-dimensional image that the pixel value can only be 0 and 1.The six-dimensional hyper-chaotic system is used to generate the swapping table which the image bits are exchanged according to.A dynamic diffusion method suitable for color images is proposed in the diffusion phase to make the pixels of each color component interact with others,which enhancing the security performance of the encryption algorithm.