Paper 2026/228

SCA-MAYO: Demystifying Side-channel Security of MAYO Signature Scheme

Abstract

Multivariate quadratic (MQ)-based digital signature schemes are promising candidates for the ongoing post-quantum (PQ) standardization procedure due to their compact signatures and fast verification. However, the side-channel security of their recent optimized and protected implementations remains underexplored. This work presents novel side-channel attacks on the MQ-based signature scheme MAYO, targeting both unprotected and masked implementations. We develop the first non-profiled single-trace correlation power attack against the recent nibble-sliced implementation of MAYO. Next, we evaluate two masking approaches proposed for MQ-based signatures. Our findings indicate that masking sensitive variables alone leaves the implementation vulnerable to single-trace attacks, and that masking only public variables also fails to provide the intended protection. To assess the second case, we consider both profiled and blind adversaries. The blind setting adopts a recent deep-learning-based blind side-channel analysis framework and demonstrates secret-key recovery without access to the masked public values or a cloned device. We validate our attacks on an STM32F3 Cortex-M4 platform and demonstrate that recently proposed countermeasures do not provide adequate protection against realistic single-trace adversaries. Finally, we discuss how the underlying attack methodology extends to other MQ-based signature schemes and present a strengthened masking and refreshing countermeasure that mitigates the proposed attacks.