Nonlinearity Improvement for Ascon Substitution Box

: The technological scene is developing towards employing tiny-sized devices. For a variety of functions that encompass sensing, identification, and decision-making. These devices are restricted in their resources to be secure. The National Institute of Standards and Technology (NIST) has published the Ascon, a standard lightweight cryptography (LWC) algorithm for data gathered by restricted devices in 2023. The fundamental function of Ascon is the permutation function. The main core of the permutation function is the substitution box (S-box). This paper proposes an S-box based on chaotic systems using coupled map lattices (CML), which agrees with LWC algorithms due to its low complexity. The proposed S-box suggests high performance and security for restricted devices. The security robustness is tested using various cryptographic criteria, such as nonlinearity, strict avalanche criteria, and differential approximation probabilities. The proposed S-box approaches significant resistance to both linear and differential cryptanalysis. So, it could be replacing the substitution and linear diffusion layers of Ascon permutation to improve the nonlinearity and randomness.