Multi-image cipher based on the random walk of Knight in a virtual 3D chessboard

Abstract

This study proposes a novel, efficient and a secured multiple color images encryption scheme based on the random walk of knight in a virtual 3D chessboard, chaotic system and SHA256 hashing. First of all, a perfect square number of color images are input. These images are decomposed into their red, green and blue components. These components are stacked together to get a 3D image. Three intensity values from this 3D image are randomly chosen. These values serve as the starting address for the knight to start its scrambling project. This act increases both the key space and plaintext sensitivity. Next, this 3D image is converted into 1D image for the scrambling process. Knight - a chess piece, has been commissioned to walk randomly in the 3D chessboard in all the three coordinate planes for an arbitrary number of times. The movement of knight in the 3D chessboard has been linked with the transferring of pixels from the 1D image to the scrambled 3D image. In this way, the input images are abundantly scrambled. Lastly, an XOR operation has been carried out to throw the diffusion effects. The three chaotic vectors given by the intertwining logistic map have been used in the selection of planes, mode of movement of knight and the diffusion process. SHA-256 hash codes for the given input color images have been used for the plaintext sensitivity. Security analyses and the computer experiments suggest the desirable security effects and prospects for some real world application of the proposed cipher. Information entropy obtained by the proposed algorithm is 7.9999.