Michael Yue

Date of Award


Document Type



Santa Clara : Santa Clara University, 2021.

Degree Name

Master of Science (MS)


Electrical and Computer Engineering

First Advisor

Sara Tehranipoor


The demand of integrated circuits (IC)s are increasing and the industry has outsourced the fabrication process to untrusted environments. An adversary at these untrusted facilities can reverse engineer parts of the IC to reveal the original design. IC piracy and overproduction are serious issues that threaten the security and integrity of a system. These ICs can be copied illegally and altered to contain malicious hardware. The pirated ICs can be placed in consumer products which may harm the system or leak sensitive information. Hardware obfuscation is a technique used to protect the original design before it gets fabricated, tested, assembled, and packaged. Hardware obfuscation intends to hide or alter the original design of a circuit to prevent attackers from determining the true design. Logic locking is a type of hardware obfuscation technique where additional key gates are inserted into the circuit. Only the correct key can unlock the functionality of that circuit otherwise the system produces the wrong output. In an effort to hinder these threats on ICs, we have developed a probability-based logic locking technique to protect the design of a circuit. Our proposed technique called ProbLock can be applied to combinational and sequential circuits through a critical selection process. We used a filtering process to select the best location of key gates based on various constraints. The main constraint is based on gate probabilities in the circuit. Each step in the filtering process generates a subset of nodes for each constraint. We also integrated an anti-SAT technique into ProbLock to enhance the security against a specific boolean satisfiability (SAT) attack. We analyzed the correlation between each constraint and adjusted the strength of the constraints before inserting key gates. We adjusted an optimized ProbLock to have a small overhead but high security metric against SAT attacks. We have tested our algorithm on 40 benchmarks from the ISCAS ’85 and ISCAS ’89 suite. ProbLock is evaluated using a SAT attack on the benchmark and measuring how well the attack performs on the locked circuit. Finally, we compared ProbLock to other logic locking techniques and discussed future steps for this project.