Countering Side-Channel Attacks With a Dynamic S-Box Based on Affine Transformations and Gold Sequences

Advanced cryptographic devices employ multiscale countermeasures to bolster resilience against side-channel analysis (SCA). In masking-based defenses, secure substitution-boxes (S-boxes) and effective masking schemes are paramount. Additionally, the time-based hiding techniques, leveraging multiple clocks for individual encryption operations, offer significant protection. This article introduces a novel multiscale countermeasure: an improved tower field masking scheme integrated with an affine transformation-based dynamic S-box. Crucially, we incorporate Gold sequences to generate both a random clock source for horizontal hiding and random values for masking. Extensive evaluation using up to five million power traces demonstrates the robustness of our approach against standard correlation power analysis (CPA) and alignment preprocessing techniques, including sliding window and amplitude peak localization. Experimental results show a measurement-to-disclosure (MTD) improvement of at least <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$150\times $</tex-math> </inline-formula> compared to unprotected implementations using stand-alone masking and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$375\times $</tex-math> </inline-formula> with our multiscale approach. Furthermore, we demonstrate resilience against recent robust profiled deep learning SCA, which could only recover four subkeys even with one million traces.