A Side-Channel Analysis Resistant Description of the AES S-Box

So far, efficient algorithmic countermeasures to secure the AES algorithm against (first-order) differential side-channel attacks have been very expensive to implement. In this article, we introduce a new masking countermeasure which is not only secure against first-order side-channel attacks, but which also leads to relatively small implementations compared to other masking schemes implemented in dedicated hardware. Our approach is based on shifting the computation of the finite field inversion in the AES S-box down to GF(4). In this field, the inversion is a linear operation and therefore it is easy to mask. Summarizing, the new masking scheme combines the concepts of multiplicative and additive masking in such a way that security against first-order side-channel attacks is maintained, and that small implementations in dedicated hardware can be achieved.