Countermeasures and Advanced Attacks
Brice Colombier, Vincent Grosso · 2025
This chapter presents the main algorithmic countermeasures for protecting software implementations of cryptographic algorithms against side-channel attacks. It illustrates the various countermeasures by taking the AES symmetric encryption algorithm as an example, and, more specifically, the first nonlinear transformation of the encryption: the SubBytes transformation of the first round. The main advantage of shuffled operations, as opposed to previous countermeasures, is that the general pattern observable in successive traces remains identical . The noise inherent in the operation of electronic circuits makes attacks more difficult, since it masks (to some extent) the relationship between the secret data manipulated and the trace obtained by observation of side channels. The aim of masking is to force the attacker to combine several points on the trace in order to carry out the attack. The first countermeasures we saw were designed to shift the time at which a sensitive operation is carried out.