Security-Enhanced Image Encryption: Combination of S-Boxes and Hyperchaotic Integrated Systems

In the field of image encryption, with the continuous development of attack techniques, the requirements for the attack resistance and robustness of encryption algorithms are increasing, and the method of image encryption using a single chaotic system can no longer provide sufficient security and randomness. In this paper, an image encryption method combining S-box and hyperchaotic integrated system is proposed. First, a particle swarm optimization algorithm is designed to search for S-boxes based on an adaptive function that takes into account several security metrics and an S-function inertia weighting strategy. The S-box obtained from the search has good performance index, in which the nonlinearity is 110, the differential uniformity is 6, the algebraic number is 7, and the strict avalanche criterion coefficient is 0.50415. Further, a hyperchaotic integrated system is constructed by combining the Lorenz system and the Henon system with the hyperchaotic Chen system as the core. A three-step diffusion mechanism is adopted in the encryption process, and the S-boxes obtained from the search of the particle swarm optimization algorithm are fully integrated with the chaotic sequences generated by the hyperchaotic integrated system in the first two steps of diffusion to improve the security and randomness of the encryption algorithm. The performance of the proposed encryption algorithm is evaluated and the average values of the calculated metrics are as follows: information entropy value is 7.993, correlation coefficient is 0.008803, NPCR is 99.61%, and UACI is 33.48%. Therefore, the proposed image encryption algorithm combining S-boxes and a hyperchaotic integrated system has high security and robustness, making it applicable to the field of highly demanding image encryption.