Side-Channel Attack against RSA Key Generation Algorithms

Many applications of embedded devices require the generation of cryptographic secret parameters during the life cycle of the product. In such an unsafe context, several papers have shown that key generation algorithms are vulnerable to side-channel attacks. This is in particular the case of the generation of the secret prime factors in RSA. Until now, the threat has been demonstrated against naive implementations whose operations’ flow depends on secret data, and a simple countermeasure is to avoid such kind of dependency. In this paper, we propose a new attack that renders this defence strategy ineffective. It is in particular able to break secure implementations recommended by the ANSI X9.31 and FIPS 186-4 standards. We analyse its efficiency for various realistic attack contexts and we demonstrate its practicality through experiments against a smart-card implementation. Possible countermeasures are eventually proposed, drawing the following main conclusion: prime generation algorithms should avoid the use of a prime sieve combined with a deterministic process to generate the prime candidates from a random seed.