On the Approximation Resiliency of Logic Locking and IC Camouflaging Schemes

The SAT-based attacks are extremely successful in deobfuscating the traditional combinational logic locking and IC camouflaging schemes. While several SAT-resilient protection schemes that increase the minimum query count of the attack have been proposed recently, none of them satisfy the output corruptibility (error) criteria. Therefore, most of them were combined with high corruptibility schemes to achieve both corruptibility and high query count. These “compound” schemes are successful since existing SAT attacks are agnostic to the corruptibility of the protection scheme. In this paper, we propose an approximate SAT-based attack framework which focuses on the iterative convergence of an attack toward a better solution. This helps our attack reduce a compound scheme to a standalone SAT-resilient scheme. In addition, we relate the problem of minimum query count to a well-known graph problem, and we propose a novel technique to increase the corruptibility of SAT-resilient protection schemes in a controllable manner. This creates protection schemes that have both high query count and corruptibility. Furthermore, due to the approximation resiliency property of these schemes, approximate attacks provide no advantage over exact attacks when attacking them.