Towards Leakage Exploitation Optimality in Profiled Side-Channel Attacks

Template Attack is widely accepted to be one of the most powerful side-channel attacks, because it is usually assumed that one has a full knowledge of targeted crypto devices and thus be well capable of characterizing the side-channel leakages. However, the question of whether Template Attack is really optimal in terms of leakage exploitation rate is still unclear. In this paper, we present a negative answer to this crucial question, by introducing a normalization process into classical Template Attack. On the theoretical side, we prove that our normalized Template Attack is (strictly) better in terms of leakage exploitation rate than classical Template Attack; on the practical side, we evaluate the key-recovery efficiency of normalized Template Attack and its classical counterpart as well under identical scenarios, by performing attacks against both simulated and real power traces. Our experimental results show that the proposed method is valid end effective. Interestingly enough, this normalization is of extremely low computation cost, and thus is very easy-to-use in practice. Therefore, we argue that this normalization should be integrated into profiled attacks as one necessary step in the future, so that one could better understand the practical threats of them.