International Association
for Cryptologic Research

In the context of post-quantum secure algorithms like CRYSTALS-Kyber, the importance of protecting sensitive polynomial coefficients from side-channel attacks is increasingly recognized. Our research introduces two alternative masking methods to enhance the security of the compression function in Kyber through masking. Prior to this, the topic had been addressed by only one other research study. The "Double and Check" method integrates arithmetic sharing and symmetry adjustments, introducing a layer of obfuscation by determining coefficient values based on modular overflows. In contrast, the Look-Up-Table (LUT) integration method employs arithmetic-to-Boolean conversions, augmented by a pre-computed table for efficient value verifications. Furthermore, by leveraging the alternative prime 7681, we propose a novel masked compression function. This prime, 7681, is also notable as the smallest prime suitable for fast NTT multiplication. While both algorithms prioritize data protection and streamlined processing, they also underscore the inherent challenges of balancing computational speed with the potential vulnerabilities to side-channel attacks.