Résumé
Soft-Analytical Side-Channel Attacks (SASCAs) on lattice-based cryptography implementations have become a prominent vector of attack in the recent years, specially against the Number-Theoretic Transform (NTT). To address this issue, local masking with twiddle factors has been proposed as a countermeasure to protect the NTT against such attacks. In this paper we propose an adaptation of SASCA to local-masked NTT implementations, by modifying the factor graph representation to include the masking nodes. We evaluate the success rate of the attack with respect to the level of noise of simulated traces and the number of masks u per layer. We show that the attack proves very successful in the lower values of u , by even outperforming the attack on the unmasked case. When u is increased there is a gradual augmentation of security, which comes with an important overhead on performance. Thus, we question the practicality of this countermeasure when compared to other analyzed countermeasures in the state of the art, such as shuffling.