Designing a block cipher or cryptographic permutation can be approached in many different ways. One such approach, popularized by AES, consists in grouping the bits along the S-box boundaries, e.g., in bytes, and in consistently processing them in these groups. This aligned approach leads to hierarchical structures like superboxes that make it possible to reason about the differential and linear propagation properties using combinatorial arguments. In contrast, an unaligned approach avoids any such grouping in the design of transformations. However, without hierarchical structure, sophisticated computer programs are required to investigate the differential and linear propagation properties of the primitive. In this paper, we formalize this notion of alignment and study four primitives that are exponents of different design strategies.We propose a way to analyze the interactions between the linear and the nonlinear layers w.r.t. the differential and linear propagation, and we use it to systematically compare the four primitives using non-trivial computer experiments. We show that alignment naturally leads to different forms of clustering, e.g., of active bits in boxes, of two-round trails in activity patterns, and of trails in differentials and linear approximations.
Many digital systems need to provide cryptographic 1 capabilities. A large part of these devices is easily accessible 2 by the malicious user, and may be vulnerable to side channel 3 attacks such as power or electromagnetic analysis. From one 4 side, the designer has to protect the architecture with proven 5 countermeasures; on the other, the actual implementation must 6 be validated in order to prove the absence of undesired leakages.7In this paper, we present an implementation of two optimized 8 and proven masking schemes of order 3 and 7 for an embedded 9 software AES, and prove its robustness by showing the absence 10 of significant leakage in the nonlinear layer.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.