A novel color image encryption algorithm based on substitution box and hyper-chaotic system with fractal keys

In this paper, a novel color image encryption scheme based on fractals, substitution box and hyper chaotic dynamic is proposed. In the first step, fractal images are generated by Julia fractal set as keys. Then, the substitution box is constructed by Hilbert fractal, and the original image pixels are replaced with the values of the S-box. In the next step, using the Logistic map, the location of the pixels is scrambled to reduce their correlation. In the following, Chen hyper-chaotic system is used to change the pixels values of fractal images as well as index production to select fractal images. Finally, each pixel of three original image layers with the corresponding pixels in the three selected fractal images and the previous encrypted pixel value are encrypted with XOR operation. Both experimental results and security analyses indicated that the proposed method yields high encryption effect, larger secure key space and is high sensitive to the secret key and the plain image. In addition, the algorithm could resist against diverse typical attacks.