A Provably Secure and Efficient Countermeasure against Timing Attacks

We show that the amount of information about the key that an unknown-message attacker can extract from a deterministic side-channel is bounded from above by |O| log₂(n + 1) bits, where n is the number of side-channel measurements and O is the set of possible observations. We use this bound to derive a novel countermeasure against timing attacks, where the strength of the security guarantee can be freely traded for the resulting performance penalty. We give algorithms that efficiently and optimally adjust this trade-off for given constraints on the side-channel leakage or on the efficiency of the cryptosystem. Finally, we perform a case-study that shows that applying our countermeasure leads to implementations with minor performance overhead and formal security guarantees.