Making RSA–PSS Provably Secure against Non-random Faults

International audienceRSA–CRT is the most widely used implementation for RSA signatures. However, deterministic and many probabilistic RSA signatures based on CRT are vulnerable to fault attacks. Nevertheless, Coron and Mandal (Asiacrypt 2009) show that the randomized PSS padding protects RSA signatures against random faults. In contrast, Fouque et al. (CHES 2012) show that PSS padding does not protect against certain non-random faults that can be injected in widely used implementations based on the Montgomery modular multiplication. In this paper, we prove the security of an infective countermeasure against a large class of non-random faults; the proof extends Coron and Mandal's result to a strong model where the adversary can choose the value of the faulty signatures modulo one of the prime factors of the RSA modulus. This fault model is clearly strictly more general than Coron and Mandal's, and it captures most of the non-random faults of Fouque et al. Such non-random faults induce, together with the infective countermeasure, more complex probability distributions than in the original proof; we analyze them using careful estimates of character sums over finite fields. The security proof is formally verified using appropriate extensions of EasyCrypt, and provides the first application of formal verification to provable (i.e. reductionist) security in the context of fault attacks

Modeling and Verifying Security Protocols with the Applied Pi Calculus and ProVerif

International audienceProVerif is an automatic symbolic protocol verifier. It supports a wide range of cryptographic primitives, defined by rewrite rules or by equations. It can prove various security properties: secrecy, authentication, and process equivalences, for an unbounded message space and an unbounded number of sessions. It takes as input a description of the protocol to verify in a dialect of the applied pi calculus, an extension of the pi calculus with cryptography. It automatically translates this protocol description into Horn clauses and determines whether the desired security properties hold by resolution on these clauses. This survey presents an overview of the research on ProVerif