SCARE and power attack on AES-like block ciphers with secret S-box

Despite Kerckhoff’s principle, there are secret ciphers with unknown components for diplomatic or military usages. The side-channel analysis of reverse engineering (SCARE) is developed for analyzing secret ciphers. Considering the side-channel leakage, SCARE attacks enable the recovery of some secret parts of a cryptosystem, e.g., the substitution box table. However, based on idealized leakage assumption, most of these attacks have a few limitations on prior knowledge or implementations. In this paper, we focus on AES-like block ciphers with a secret S-box and demonstrate an attack which recovers both the secret key and the secret S-box. On the one hand, the key is recovered under profiled circumstance by leakage analysis and collision attack. On the other hand, the SCARE attack is based on mathematical analysis. It relies on Hamming weight of MixColumns intermediate results in the first round, which can restore the secret S-box. Experiments are performed on real power traces from a software implementation of AES-like block cipher. Moreover, we evaluate the soundness and efficiency of our method by simulations and compare with previous approaches. Our method has more advantages in intermediate results location and the required number of traces. For simulated traces with gaussian noise, our method requires 100000 traces to fully restore the secret S-box, while the previous method requires nearly 300000 traces to restore S-box.