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Globalized outsourcing of integrated circuit manufacturing has introduced potent security threats such as unauthorized overproduction and hardware Trojan insertion. An approach that is used to protect circuit designs from overproduction is logic locking, which introduces key inputs to a digital circuit such that only the correct key will allow the circuit to work properly and all others will cause unintended functionality. On the other hand, the majority of the existing methods to tackle hardware Trojans are in the realm of proactive prevention or static detection, but a more challenging problem, which is the run-time mitigation of the Trojans inserted in a zero-trust design flow, is yet to be solved. In this work, we look through the lens of logic locking with the goal of introducing online reconfigurability into a design and apply the fundamental principles of fault tolerance and state traversal to create an effective mitigation tactic against hardware Trojans. Redundancy is inserted at low-controllable states to create trap states for the attackers, and key inputs are added to select the active path. The strength of our proposed approach lies in its ability to circumvent Trojan payloads transparently at run-time with only a slight overhead, as demonstrated by experiments run on over 40 benchmarks of varying sizes. We also demonstrate viability when combined with secure logic locking methods to provide multi-objective security. 

The semiconductor industry must deal with different hardware threats like piracy and overproduction as a result of outsourcing manufacturing. While there are many proposals to lock the circuit using a global protected key only known to the designer, there exist numerous oracle-guided attacks that can examine the locked netlist with the assistance of an activated IC and extract the correct key. In this paper, by adopting a low-overhead structural method, we propose DK Lock, a novel Dual Key locking method that securely protects sequential circuits with two different keys that are applied to one set of key inputs at different times. DK Lock structurally adds an activation phase to the sequential circuit, and a correct key must be applied for several cycles to exit this phase. Once the circuit has been successfully activated, a new functional key must be applied to the same set of inputs to resume normal operation. DK Lock opens up new avenues for hardware IP protection by simultaneously refuting the single static key assumption of the existing attacks and overcoming the state explosion problem of state-of-the-art sequential logic locking methods. Our experiments confirm that DK Lock maintains a high degree of security with reasonable power and area overheads.