Robust medical and color image cryptosystem using array index and chaotic S-box

Abstract

Providing robust security within an image cryptosystem during network communication is more essential than ever, highlighting the fundamental aspects of confusion and diffusion. This study presents a novel approach for securely transmitting images through insecure channels, using array index manipulation for scrambling and simple pixel-level confusion and diffusion through XOR operations, effectively involving row and column permutation to achieve robust scrambling. This method operates two layers of confusion by rearranging array indexes using a Tent map and constructing an S-box algorithm derived from the Henon map, while the diffusion process uses a pseudo-random sequence generator based on the Henon map, with their chaotic dynamics analyzed through investigations of Lyapunov exponents and bifurcation diagrams. The expanded chaotic range and improved effects of chaotic maps produce new S-boxes with satisfactory cryptographic performance, including balancedness and non-linearity, with S-box3 achieving the highest non-linearity at 108. Following a performance and security assessment of the proposed technique, it has been found that the entropy value for the cipher image is nearly 7.998; also, the NPCR and UACI values for the cipher images are 99.6 and 33.4, respectively, and it demonstrates closeness to the ideal value. Finally, the proposed method demonstrates high randomness, undergoes evaluation using the NIST test suite, has good operation efficiency, and exhibits resilience against various attack forms such as statistical, differential, data-loss, and noise attacks, affirming its security and relevance for real-time cryptosystems.