Encryption scheme for multi-image based on combination of multiple chaotic maps and iterative variation of confusion keystream and mixed diffusion expression

To tackle the issue of efficiency and security in the multi-image encryption scheme, a scheme is designed. Firstly, the combination of the keystreams of hyperchaotic map and fractional-order Lorenz system are selected for the scheme. Then, multiple images are reshaped into a vector and the vector is reshaped into a cube. A first type of diffusion is performed on the cube and this procedure is based on mixed arithmetic operations. The diffusion equation is characterized by both a plaintext delay term and a ciphertext feedback term. Secondly, the cube is then confused in a point-to-point manner by the scheme, and the large cube is segmented into four or eight small cubes. The segmentation schemes are determined by plaintext parameter. The rotation of small cube is selected according to the different schemes, and a point-to-point confusion is used to confuse the small cubes that are not rotating. The confusion procedure of small cube is similar to the first confusion step. Then, a combination method corresponding to the cube segmentation method is used to combine the small cubes into a large cipher cube, which is similar to the game of segmenting and assembling building block. Thirdly, the second type of diffusion has different mixed arithmetic expressions. The keystream values are changed according to the parameter values of iteration during the confusion procedure. The relative positions of the keystreams are made variable to increase the difficulty of brute-force cracking. Simulation results and security analysis demonstrate that images can be efficiently and securely encrypted.