Confused by Confusion: Systematic Evaluation of DPA Resistance of Various S-boxes

When studying the DPA resistance of S-boxes, the research community is divided in their opinions on what properties should be considered. So far, there exist only a few properties that aim at expressing the resilience of S-boxes to side-channel attacks. Recently, the confusion coefficient property was defined with the intention to characterize the resistance of an S-box. However, there exist no experimental results or methods for creating S-boxes with a “good” confusion coefficient property. In this paper, we employ a novel heuristic technique to generate S-boxes with “better” values of the confusion coefficient in terms of improving their side-channel resistance. We conduct extensive side-channel analysis and detect S-boxes that exhibit previously unseen behavior. For the 4 × 4 size we find S-boxes that belong to optimal classes, but they exhibit linear behavior when running a CPA attack, therefore preventing an attacker from achieving 100% success rate on recovering the key.