Mitigating SAT Attack on Logic Locking

Logic locking is a technique that has been proposed to protect outsourced IC designs from piracy and counterfeiting by untrusted foundries. A locked IC preserves the correct functionality only when a correct key is provided. Recently, the security of logic locking is threatened by a new attack called SAT attack, which can decipher the correct key of most logic locking techniques within a few hours [12] even for a reasonably large number of keys. This attack iteratively solves SAT formulas which progressively eliminate the incorrect keys till the circuit unlocked. In this paper, we present a circuit block (referred to as Anti-SAT block) to thwart the SAT attack. We show that the number of SAT attack iterations to reveal the correct key in a circuit comprising an Anti-SAT block is an exponential function of the key-size thereby making the SAT attack computationally infeasible. Through our experiments, we illustrate the effectiveness of our approach to securing modern chips fabricated in untrusted foundries.