Single-Trace Side-Channel Attacks on Ω-Small Polynomial Sampling

Abstract

This paper proposes a new single-trace side-channel attack on lattice-based post-quantum protocols. We target the.-small polynomial sampling of NTRU, NTRU Prime, and CRYSTALS-DILITHIUM algorithm implementations (which are NIST Round-3 finalist and alternative candidates), and we demonstrate the vulnerabilities of their sub-routines to a power-based side-channel attack. Specifically, we reveal that the sorting implementation in NTRU/NTRU Prime and the shuffling in CRYSTALS-DILITHIUM's omega-small polynomial sampling process leaks information about the '-1', '0', or '+1' assignments made to the coefficients. We further demonstrate that these assignments can be found within a single power measurement and that revealing them allows secret and session key recovery for NTRU/NTRU Prime, while reducing the challenge polynomial's entropy for CRYSTALS-DILITHIUM. We execute our proposed attacks on an ARM Cortex-M4 microcontroller running the reference software submissions from NIST Round-3 software packages. The results show that our attacks can extract coefficients with a success rate of 99.78% for NTRU and NTRU Prime, reducing the search space to 2(41) or below. For CRYSTALS-DILITHIUM, our attack recovers the coefficients' signs with over 99.99% success, reducing rejected challenge polynomials' entropy between 39 to 60 bits. Our work informs the proposers about the single-trace vulnerabilities of their software and urges them to develop single-trace resilient software for low-cost microcontrollers.