Masking and Leakage-Resilient Primitives: One, the Other(s) or Both?

Abstract. Securing cryptographic implementations against side-channel attacks is one of the most important challenges in modern cryptography. Many countermeasures have been introduced for this purpose, and ana-lyzed in specialized security models. Formal solutions have also been pro-posed to extend the guarantees of provable security to physically observ-able devices. Masking and leakage-resilient cryptography are probably the most investigated and best understood representatives of these two approaches. Unfortunately, claims whether one, the other or their com-bination provides better security at lower cost remained vague so far. In this paper, we provide the first comprehensive treatment of this impor-tant problem. For this purpose, we analyze whether cryptographic im-plementations can be security-bounded, in the sense that the time com-plexity of the best side-channel attack is lower-bounded, independent of the number of measurements performed. Doing so, we first put forward a significant difference between stateful primitives such as leakage-resilien