Physical functions: the common factor of side-channel and fault attacks?

Abstract

Physical attacks on cryptographic circuits were first identified in the late 1990s. These types of attacks, which are still considered very powerful, are generally classified into two main categories: “fault attacks” and “side-channel attacks.” To secure circuits against such attacks, it is crucial to develop appropriate methods and tools that enable accurate estimates of the protection mechanism’s effectiveness. Numerous studies have described such methods and tools but, to the best of our knowledge, these previous investigations have considered side-channel attacks or fault attacks but not the combination of the two types. The present article proposes a combined investigation of both main types of attack by describing them with the same terminology and the same algorithm. This approach is made possible by introducing the concept of “physical functions” as an extension of the concept of “leakage functions,” which are widely used in the side-channel community. The paper represents a first step toward applying the strong theoretical background developed for side-channel attacks to the investigation of fault attacks. Besides, the proposed approach could potentially make it easier to combine side-channel attacks with fault attacks, which could certainly facilitate the discovery of new attack paths.