Towards optimal leakage exploitation rate in template attacks

Under the assumption that one has a reference device identical or similar to the target device, and thus be well capable of characterizing power leakages of the target device, Template Attacks are widely accepted to be the most powerful side-channel attacks. However, the question of whether Template Attacks are really optimal in terms of the 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 Attacks. Specifically, our contributions are two folds. On the theoretical side, we prove that Normalized Template Attacks are better in terms of the leakage exploitation rate than Template Attacks; on the practical side, we evaluate the key-recovery efficiency of Normalized Template Attacks and Template Attacks in the same attacking scenario. Evaluation results show that, compared with Template Attacks, Normalized Template Attacks are more effective. We note that, the computational price of the normalization process is of extremely low, and thus it is very easy-to-implement in practice. Therefore, the normalization process should be integrated into Template Attacks as a necessary step, so that one can better understand practical threats of Template Attacks.