Abstract: To solve the problems of low encryption quality and poor plaintext sensitivity in the existing image encryption algorithms, an image encryption algorithm combining S-box and chaotic mapping is proposed. The Hash value of the plaintext image is used to generate the key of the chaotic system, which can operate scrambling and diffusion. In addition, the S-box is generated through the Logistic chaotic system. By using the two-dimensional Logistic mapping and Chen chaotic system to generate two chaotic sequences, which have the same image size with the plaintext image, the algorithm operates exchange and the first-order diffusion for each pixel of the image. Then, the algorithm selects the S-box elements based on the chaotic sequences to do bit XOR and XNOR operations for each pixel value, and operates the second-order and third-order diffusion on all the pixels. Simulation results and security performance analysis show that, the proposed algorithm has good encryption effect, robustness and plaintext sensitivity, and thus it can resist various attacks.

Key words: image encryption algorithm, chaotic system, S-box, scrambling and diffusion, security analysis