A novel multi-image cryptosystem based on weighted plain images and using combined chaotic maps

This paper introduces a new multi-image cryptosystem based on modified Henon map and non-linear combinations of chaotic seed maps. Based on the degree of correlation between the adjacent pixels of the plain images, a unique weight is assigned to the plain images. First, the coordinates of plain images are disrupted by modified Henon map as confusion phase. In the first step of diffusion phase, the pixels content of images are changed separately by XOR operation between confused images and matrices with suitable non-linear combination of seed maps sequences. These combinations of seed maps are selected depending on the weight of plain images as well as bifurcation properties of mentioned chaotic maps. After concatenating the matrices obtained from the first step of diffusion phase, the bitwise XOR operations are applied again between newly developed matrix and the other produced matrix from the chaotic sequences of the Logistic–Tent–Sine hybrid system, as second step of diffusion phase. The encrypted image is obtained after applying shift and exchange operations. The results of the implementation using graphs and histograms show that the proposed method requires an average of 49.31 ms less processing time than the best time of some previous methods for 1024 × 1024 images. The entropy is close to the ideal value of 8, and the values of the correlation coefficient of the encrypted images are close to 0. The histogram of the encrypted images is uniform and the value of peak signal to noise ratio (PSNR) is about 5 dB more than some compared methods for 50% cropping attack. Therefore, compared to some of the existing methods, the proposed method can also be used as a secure method for encrypting gray-scale digital images.