Abstract. Since Power Analysis on smart cards was introduced by Paul Kocher [7], many countermeasures have been proposed to protect implementations of cryptographic algorithms. In this paper we propose a new protection principle: the transformed masking method. We apply this method to protect two of the most popular block ciphers: DES and the AES Rijndael. To this end we introduce some transformed S-boxes for DES and a new masking method and its applications to the non-linear part of Rijndael.

Abstract. Since Power Analysis on smart-cards was introduced by Paul Kocher [KJJ98], the validity of the model used for smart-cards has not been given much attention. In this paper, we first describe and analyze some different possible models. Then we apply these models to real components and clearly define what can be detected by power analysis (simple, differential, code reverse engineering...). We also study, from a statistical point of view, some new ideas to exploit these models to attack the card by power analysis. Finally we apply these ideas to set up real attacks on cryptographic algorithms or enhance existing ones.

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Abstract. Differential Power Analysis (DPA) on smart-cards was introduced by Paul Kocher [11] in 1998. Since, many countermeasures have been introduced to protect cryptographic algorithms from DPA attacks. Unfortunately these features are known not to be efficient against high order DPA (even of second order). In these paper we will first describe new specialized first order attack and remind how are working high order DPA attacks. Then we will show how these attacks can be applied to two usual actual countermeasures. Eventually we will present a method of protection (and apply it to the DES) which seems to be secure against any order DPA type attacks. The figures of a real implementation of this method will be given too.

In order to protect a cryptographic algorithm against Power Analysis attacks, a well-known method consists in hiding all the internal data with randomly chosen masks. Following this idea, an AES implementation can be protected against Differential Power Analysis (DPA) by the "Transformed Masking Method", proposed by Akkar and Giraud at CHES'2001, requiring two distinct masks. At CHES'2002, Trichina, De Seta and Germani suggested the use of a single mask to improve the performances of the protected implementation. We show here that their countermeasure can still be defeated by usual first-order DPA techniques. In another direction, Akkar and Goubin introduced at FSE'2003 a new countermeasure for protecting secret-key cryptographic algorithms against high-order differential power analysis (HO-DPA). As particular case, the "Unique Masking Method" is particularly well suited to the protection of DES implementations. However, we prove in this paper that this method is not sufficient, by exhibiting a (first-order) enhanced differential power analysis attack. We also show how to avoid this new attack.