Entropy Reduction for the Correlation-Enhanced Power Analysis Collision Attack

Side Channel Attacks are an important attack vector on secure AES implementations. The Correlation-Enhanced Power Analysis Collision Attack by Moradi et al. [13] is a powerful collision attack that exploits leakage caused by collisions in between S-Box computations of AES. The attack yields observations from which the AES key can be inferred. Due to noise, an insufficient number of collisions, or errors in the measurement setup, the attack does not find the correct AES key uniquely in practice, and it is unclear how to determine the key in such a scenario. Based on a theoretical analysis on how to quantify the remaining entropy, we derive a practical search algorithm. Both our theoretical analysis and practical experiments show that even in a setting with high noise or few available traces we can either successfully recover the full AES key or reduce its entropy significantly.