Defense-in-depth: A recipe for logic locking to prevail

Logic locking/obfuscation has emerged as an auspicious solution for protecting the semiconductor intellectual property (IP) from the untrusted entities in the design and fabrication process. Logic locking disguises the implementation and functionality of the IP by implanting additional key-gates in the circuit. The right output of the locked chip is produced, once the correct key value is available at the input of the key-gates. The confidentiality of the key is imperative for the security of the locked IP as it stands as the lone barrier against IP infringement. Therefore, the logic locking is considered as a broken scheme once the key value is exposed. The logic locking techniques have shown vulnerability to different classes of attacks, such as Oracle-guided and physical attacks. Although the research community has proposed a number of countermeasures against such attacks, none of them is simultaneously unbreakable against Oracle-guided, Oracle-less, and physical attacks. Under such circumstances, a defense-in-depth mechanism can be considered as a feasible approach in addressing the vulnerabilities of logic locking. Defense-in-depth is a multilayer defense strategy where several independent countermeasures are implemented in the device to provide aggregated protection against different attack vectors.Introducing such a multilayer shielding model in logic locking is the major contribution of this paper. With regard to this, we first identify the core components of logic locking schemes, which need to be protected. Afterwards, we categorize the vulnerabilities of core components according to potential threats for the locking key in logic locking schemes. Furthermore, we propose several defense layers and countermeasures to protect the device from those vulnerabilities. In conclusion, we believe that a logic locking technique with a layered defense mechanism can be a possible solution against IP piracy.