Enhancing S-Box Nonlinearity in AES for Improved Security Using Key-Dependent Dynamic S-Box

The Advanced Encryption Standard (AES) is the most widely used symmetric and secure encryption algorithm for commercial and research purposes. The core of AES is its substitution box (S-box), which primarily provides nonlinearity, confusion, and diffusion. The improvements to nonlinearity in S-box is one of the methods used by researchers to enhance security in AES. In this paper, to increase the nonlinearity of the S-box, AES using a key-dependent dynamic S-box is implemented and compared with the AES using a static S-box. The algorithm proposed in this paper draws observation from results of security parameters like hamming distance, strict avalanche criteria (SAC), and balanced output while comparing key-dependent S-box and static AES S-box. Among 40 experimental results, the key-dependent dynamic S-box performs 22.5% times better for hamming distance observation drawn is that the hamming distance is more in the dynamic AES than static AES. The average bit difference of 10 rounds of dynamic AES is around 65%, which is a good avalanche criterion.