A Simple Power-Analysis (SPA) Attack on Implementations of the AES Key Expansion

This article presents a simple power-analysis (SPA) attack on implementations of the AES key expansion. The attack reveals the secret key of AES software implementations on smart cards by exploiting the fact that the power consumption of most smart-card processors leaks information during the AES key expansion. The presented attack efficiently utilizes this information leakage to substantially reduce the key space that needs to be considered in a brute-force search for the secret key. The details of the attack are described on the basis of smart cards that leak the Hamming weight of intermediate results occurring during the AES key expansion.