FCLock: Harnessing Functional Non-Combinational Cycles in Logic Locking

Abstract

Logic locking is an integrated circuit hardware protection technique aimed at combating reverse engineering, IP piracy, and hardware Trojans. Cyclic encryption, one of these techniques, is designed to create feedback loops in circuits to resist SAT attacks, but it was quickly compromised. In this paper, we introduce a new cyclic logic locking method, FCLock, which effectively renders SAT/CycSAT/BeSAT decryption techniques obsolete. By altering the encoding of the state machine that drives the combinational logic circuits, we functionally preserve the non-combinational logic loops. This preservation makes it impossible for attackers to decrypt the circuit by removing cycles. Experimental results demonstrate the effectiveness and security of the proposed method, as well as its low overhead.