Randomization Based Probabilistic Approach to Detect Trojan Circuits

In this paper, we propose a randomization based technique to verify whether a manufactured chip conforms to its design or is infected by any trojan circuit. A trojan circuit can be inserted into the design or fabrication mask by a malicious manufacturer such that it monitors for a specific rare trigger condition, and then it produces a payload error in the circuit which alters the functionality of the circuit often causing a catastrophic crash of the system where the chip was being used. Since trojans are activated by rare input patterns, they are stealthy by nature and are difficult to detect through conventional techniques of functional testing. In this paper, we propose a novel randomized approach to probabilistically compare the functionality of the implemented circuit with the design of the circuit. Using hypothesis testing, we provide quantitative guarantees when our algorithm reports that there is no trojan in the implemented circuit. This allows us to trade runtime for accuracy. The technique is sound, that is, it reports presence of a trojan only if the implemented circuit is actually infected. If our algorithm finds that the implemented circuit is infected with a trojan, it also reports a fingerprint input pattern to distinguish the implemented circuit from the design. We illustrate the effectiveness of our technique on a set of infected and benign combinational circuits.