STATION: State Encoding-Based Attack-Resilient Sequential Obfuscation

The unauthorized duplication of design intellectual property (IP) and illegal overproduction of integrated circuits (ICs) are hardware security threats plaguing the security of the globalized IC supply chain. Researchers have developed various countermeasures, such as logic locking, layout camouflaging, and split manufacturing, to overcome the security threat of IP piracy and unauthorized overproduction. Logic locking is a holistic solution among all countermeasures since it safeguards the design IP against untrusted entities, such as untrusted foundries, test facilities, or end-users, throughout the globalized IC supply chain. There are well-known logic locking techniques for combinational circuits with well-established security properties; however, their sequential counterparts remain vulnerable. Since most practical designs are inherently sequential, it is essential to develop secure obfuscation techniques to protect sequential designs. This article proposes a sequential obfuscation technique, STATION, building on the principles of finite state machine encoding schemes. STATION is resilient against various attacks on sequential obfuscation-input-output (I/O) query attacks and structural attacks, including the ones targeting sequential obfuscation-which have broken all state-of-the-art sequential obfuscation techniques. STATION achieves good resilience and desired security against various I/O and structural attacks, which we ascertain by launching 9 different attacks on all tested circuits. Moreover, STATION ensures tolerable overheads in power, performance, and area, such as 8.75%, 1.22%, and 5.63% on the largest tested circuit, containing 102 inputs, 7 outputs, {6.1\times 10^{4}} gates, 7 flip flops, 100 states, and {3.0\times 10^{3}} transitions.