Robert Naciri

CRT RSA algorithm protected against fault attacks

Embedded devices performing RSA signatures are subject to Fault Attacks, particularly when the Chinese Remainder Theorem is used. In most cases, the modular exponentiation and the Garner recombination algorithms are targeted. To thwart Fault Attacks, we propose a new generic method of computing modular exponentiation and we prove its security in a realistic fault model. By construction, our proposal is also protected against Simple Power Analysis. Based on our new resistant exponentiation algorithm, we present two different ways of computing CRT RSA signatures in a secure way. We show that those methods do not increase execution time and can be easily implemented on low-resource devices.

Optimal use of montgomery multiplication on smart cards

Montgomery multiplication is used to speed up modular multiplications involved in public-key cryptosystems. However, it requires conversion of parameters into N-residue representation. These additional pre-computations can be costly for low resource devices like smart cards. In this paper, we propose a new, more efficient method, suitable for smart card implementations of most of public-key cryptosystems. Our approach essentially consists in modifying the representation of the key and the algorithm embedded in smart card in order to take advantage of the Montgomery multiplication properties.