Novel Dynamic State-Deflection Method for Gate-Level Design Obfuscation

The emerging security threats in the integrated circuit supply chain do not only challenge the chip integrity, but also raise serious concerns on hardware intellectual property (IP) piracy. Hardware design obfuscation is a promising countermeasure to resist reverse engineering attacks and IP piracy. The majority of existing hardware obfuscation methods modify the original finite state machine (FSM) by adding additional state transitions and utilizing a key sequence to lock the transition from the nonfunctional states to the functional reset state. Those methods are effective to prevent attackers from entering the normal functional mode but they lack resilience if the FSM is already in the normal mode. This paper proposes to protect all the states with a low-cost state-deflection-based obfuscation method, which dynamically deflects state transitions from the original transition path to a black hole cluster if a wrong key is applied. Unlike other works that use static transitions between legal states to black hole states at the design time, this method utilizes a state rotation function (Rotatefunc) and selective register flipping function (Mapfunc) to dynamically control the state deflection paths. Hence, the difficulty of reverse engineering and thwarting register overwrite attacks is increased. Simulations performed on ISCAS'89 benchmark circuits show that the proposed method significantly reduces the difference of the net toggle activities between the correct and wrong key scenarios, and achieves up to 56% higher code coverage than the most efficient obfuscation method. Thanks to the dynamic deflection feature, on average, this method generates about 100 more unique state register patterns than other methods with moderate power increase. Moreover, the proposed method achieves the Hamming distance of primary outputs and state registers close to 50%.