Paper 2025/181 Original: eprint.iacr.org/2025/181 ↗

Combined blinding Side-Channel and Fault countermeasures for Lattice-Based schemes

Abstract

In this paper, we revisit and enhance two blinding countermeasures aimed at protecting implementations of lattice‑based cryptographic schemes against side‑channel and fault‑injection attacks. First, we build upon the Number Theoretic Transform (NTT) blinding technique introduced by Ravi et al., and optimize the use of blinding twiddle factors so as to maximize their number without increasing the total number of modular multiplications. Second, we improve the Chinese Remainder Theorem (CRT)–based blinding scheme proposed by Heinz and Pöppelmann by substantially reducing the randomness‑sampling overhead and streamlining the associated fault‑detection mechanism. Importantly, the two countermeasures are fully compatible and can be seamlessly combined to provide enhanced resistance to both classical and soft‑analytical side‑channel attacks, as well as fault‑injection attacks, while maintaining a performance overhead comparable to existing approaches. We demonstrate the practicality of our proposals through a proof‑of‑concept implementation integrated into Kyber/ML‑KEM.