This article presents a dynamic 4 × 4 S-Box construction for UL–AES based on Square Polynomial Transformation and Permutation (SPTP), designed to enhance resistance against linear and differential cryptanalysis while maintaining lightweight performance. The proposed construction generates key-dependent S-Boxes through a composition of bijective transformations, ensuring that a valid permutation is produced for all key-derived parameters. Security evaluation is conducted over a population of 100 independently generated S-Boxes derived from distinct encryption keys. Population-level statistical analysis is reported using aggregate measures, including minimum, maximum, mean, and standard deviation, for standard cryptographic criteria such as nonlinearity (NL), strict avalanche criterion (SAC), bit independence criterion (BIC), linear approximation probability (LAP), and differential uniformity (DU). The results indicate consistent cryptographic properties across the evaluated population, with no weak or degenerate S-Box instances observed. While individual SAC entries exhibit expected dispersion around the ideal probability of 0.5 due to the compact 4 × 4 domain, the aggregate statistics confirm balanced diffusion behavior. A representative S-Box instance is presented for illustration purposes only and is not selected based on best-case performance. Performance evaluation on an ESP8266 microcontroller shows that the proposed dynamic UL–AES achieves throughput in the tens of KB/s range, incurring a modest overhead compared to static UL–AES while remaining suitable for resource-constrained IoT applications. Overall, the results demonstrate that the proposed SPTP-based dynamic UL–AES achieves a practical balance between cryptographic strength and efficiency.
Lesmana et al. (2026) studied this question.