S5: Combining white-box countermeasures to resist state-of-the-art attacks
Alex Charlès, Aleksei Udovenko · IACR Transactions on Cryptographic Hardware and Embedded Systems · 2026
In white-box cryptography, the DCA attack broke early encoding-based countermeasures, leading to the utilization of masking schemes against a surge of local attacks. The recent filtering attack from CHES 2024 broke the last viable masking scheme from CHES 2021, which resisted both computational and algebraic attacks, raising the need for new countermeasures.In this work, we propose two countermeasures in the white-box setting by performing the first formal study of the combinations of existing countermeasures and demonstrating that applying Dummy Shuffling (EUROCRYPT 2021) then ISW masking (CRYPTO 2003) to a circuit carries algebraic, correlation, and filtering security - necessary conditions to withstand state-of-the-art non-invasive local attacks. We also show that applying these two countermeasures in the opposite order leads to a rather strong higher-order filtering (HOF) attack, highlighting the importance of the order of application of the combined countermeasures.We also propose a new masking scheme called S5, standing for Semi-Shuffled Secret Sharing Scheme, a scheme merging Dummy Shuffling and ISW in a single countermeasure more efficiently than a direct composition.