Paper 2025/679 Original: eprint.iacr.org/2025/679 ↗

Efficient SPA Countermeasures using Redundant Number Representation with Application to ML-KEM

Abstract

Simple power analysis (SPA) attacks and their extensions, profiled and soft-analytical side-channel attacks (SASCA), represent a significant threat to the security of cryptographic devices and remain among the most powerful classes of passive side-channel attacks. In this work, we analyze how numeric representations of secrets can affect the amount of exploitable information leakage available to the adversary. We present an analysis of how mutual information changes as a result of the integer ring size relative to the machine word-size. Furthermore, we study the Redundant Number Representation (RNR) countermeasure and show that its application to ML-KEM can resist the most powerful SASCA attacks and provides a low-cost alternative to shuffling. We eval- uate the performance of RNR-ML-KEM with both simulated and prac- tical SASCA experiments on the ARM Cortex-M4 based on a worst-case attack methodology. We show that RNR-ML-KEM sufficiently renders these attacks ineffective. Finally, we evaluate the performance of the RNR-ML-KEM NTT and INTT and show that SPA security can be achieved with a 62.8% overhead for the NTT and 0% overhead for the INTT relative to the ARM Cortex-M4 reference implementation used.