Circuit Obfuscation

Andrew Goffin, class of 2017, is conducting research on circuit obfuscation, the practice of hiding certain parts of the circuit for certain privacy protection.

When hardware is designed, it is often patented to become intellectual property. People can use the intellectual property by reverse engineering the circuit or using unauthorized circuit copies, without the permission of the original creator.

To try and avoid intellectual property privacy, engineers can use circuit obfuscation to hide parts of the circuit or lock the functionality of a circuit behind a “password.”

Implementing security on a hardware level, rather than just through software, makes the security much more difficult to break. Someone can bypass software by something as simple as bypassing a firewall, but cracking hardware often requires special tools or hardware access.

Circuit obfuscation can protect circuits with keys, which locks the circuit to everyone without a key.  Engineers strategically place logic gates in the circuit to potentially change the system’s output. Using the correct key the logic gates do not affect a circuit’s operation. But, if the incorrect key is used, the logic gate will begin inverting values, changing 1s to 0s and vice versa.  Without the proper values, the circuit will not function correctly.

In the example above, the XOR gate acts as the "lock" of the circuit. If you input the incorrect value for the key, the XOR gate inverts the output of AND3, thus potentially changing the output of the circuit. In this case, a key value of '1' will cause the circuit to output an incorrect value, while a key value of '0' causes the right circuit to behave exactly like the left circuit.

Note that if both C and D are 1, the XOR gate becomes irrelevant in this example. This can be considered a security flaw in the design, and is why further research is being done on the topic.

To begin learning circuit obfuscation, Goffin said to begin learning digital logic design and some basic crptography. It is important to understand the basic principles, as circuit obfuscation depends on digital design.