Homework 8

Based on your understanding about this lecture, please describe what is the IC piracy problem and why logic locking can be a solution to that problem.

1. Unauthorized copying of chips

2. An IC can only be unlocked with the correct key

We discussed a circuit obfuscation mechanism presented in a DATE 2008 paper: “J. A. Roy, F. Koushanfar, I. L. Markov, EPIC: Ending Piracy of Integrated Circuits, Design, Automation and Test in Europe (DATE), pp. 1069-1074, 2008”. There is one important step named “combinational locking” in this work. Please describe what is combinational locking and how it works using a small example.

Combinational locking is to modify circuit by XORing some wires with a common key. With the right key the circuit works, with a wrong key signals are flipped producing a wrong output

We discussed at least 4 potential attacks on logic locking, such as brute-force attack, fault analysis attack, simple SAT attack, SAT attack, and bypass attack. Based on your understanding, please discuss whether each attack would be effective/ineffective in compromising logic locking and the reason why.

• Brute-force attack

  • ineffective, only works small scale

• Fault analysis attack

  • sometimes effective, depends where locking gates are

• simple SAT attack

  • ineffective, only works small scale

• SAT attack

  • effective, uses input/output examples to find correct key

• Bypass attack

  • effective, fixes few wrong outputs

Can you provide an example of SAT-resistant logic locking mechanism? How does it work, and do you think it could be subject to any other attacks?

• SARLock

• limits each SAT iteration to remove only one wrong key

• bypass attack