On the Vulnerability of Low Entropy Masking Schemes

Low Entropy Masking Schemes (LEMS) have been proposed to offer a reasonable tradeoff between the good protection against side-channel attacks offered by masking countermeasures and the high overhead that results from their implementation. Besides the limited analysis done in the original proposals of LEMS, their specific leakage characteristics have not yet been analyzed. This work explores the leakage behavior of these countermeasures and shows two different methods how the leakage can be exploited, even by generic univariate attacks. In particular, an attack that exploits specific properties of RSM for AES as well as a more generic attack making very little assumptions about the underlying LEMS are introduced. All attacks are practically verified by applying them to publicly available leakage samples of the RSM countermeasure.