An Algebraic Approach for Evaluating Random Probing Security With Application to AES

We employ an algebraic approach to estimate the success rate of a sidechannel adversary attacking secrets of a masked circuit within the Random Probing Model (RPM), where intermediate variables of the implementation leak with a probability p. Our method efficiently handles masked linear circuits, enabling security bound estimation for practically large masking orders. For non-linear circuits, we employ a linearization technique. To reason about the security of complex structures like an S-box, we introduce a composition theorem, reducing the RPM security of a circuit to that of its constituent gadgets. Moreover, we lower the complexity of the multiplication gadget of CHES 2016 from O(n2 log(n)) to O(n2) while demonstrating its conjectured RPM security. Collectively, these novel methods enable the development of a practical masking scheme with O(n2) complexity for AES, maintaining security for a considerably high leakage rate p ≤ 0.02 ≈ 2−5.6.