Search

SAT Attack, CycSAT, and Removal Attack have demonstrated their abilities to break most existing logic locking methods. In this article, we propose a new cyclic logic locking method to invalidate these attacks simultaneously. Our main intention is to create noncombinational cycles to lock a circuit. Specifically, the noncombinational behavior in the noncombinational cycles that is unobservable at the primary outputs (POs) needs to be preserved when the correct key-vector is fed to resist CycSAT, and the noncombinational behavior in the noncombinational cycles affecting POs needs to be preserved when the incorrect key-vector is fed to invalidate SAT Attack. Furthermore, some nodes will be removed when applying our locking method, which is able to defend Removal Attack. The experimental results show the effectiveness and low area overhead of the proposed method.

Logic locking is a technique used for intellectual property protection. An effective attacking method based on satisfiability (SAT) algorithm, known as SAT attack, was proposed to decrypt an encrypted design successfully. To strengthen logic locking, this paper proposes a glitch-based logic locking method designed for sequential circuits. The proposed new schemes of key-gates can generate glitches, and use rising and falling transitions as key-inputs for the comprehensive logic locking. Experimental results show that the proposed glitch key-gate (GK) has high capability to be embedded in a set of IWLS2005 Benchmarks [22]. The cell area overhead in the designs encrypted with GKs are 10.68%, 12.22%, and 26.11% on average for encryptions with 8, 16, and 32 key-inputs, respectively, and the overhead can be reduced substantially when the GKs are combined with other logic locking methods.