🤖 AI Summary
This work investigates higher-order differential security of cryptographic functions over finite fields, focusing on the second-order zero-differential spectrum—the quantitative measure of second-order zero-difference uniformity. Methodologically, it integrates finite-field algebra, Walsh transform theory, exponential sum estimation, and combinatorial counting techniques. Theoretical contributions include: (i) a rigorous characterization of fundamental differences in higher-order differential behavior between power functions (e.g., Gold and Kasami functions) and non-power functions; and (ii) complete determination of the second-order zero-differential spectra for several important S-box families, revealing significantly narrower value ranges compared to their first-order counterparts. These results provide a more precise analytical tool for evaluating resistance against higher-order differential cryptanalysis and extend the mathematical framework for nonlinear function security analysis.