Abstract
Algebraic Side-channel attacks (ASCA) have been recently introduced as a powerful cryptanalysis technique against block cipher. These attacks represent both a target algorithm and its physical information leakages as an over-defined system of equations that the adversary tries to solve. In this paper, we apply ASCA to the SMS4 key schedule based on Hamming weight model. Experiments show that ASCA are still applicable in this context, 8 rounds of consecutive leakages can solve for the key with in 20 seconds and 24 rounds of randomly distributed leakages can solve for the key within 40 seconds.