Fundamental Study on Detecting Hardware Trojans in Printed Circuit Boards Using Ring Oscillators

Threats arise when malicious circuits, known as hardware trojans (HT), are inserted into information devices, compromising security. These HTs can be inserted during the design and manufacturing process of devices, and thus, methods to detect them at the time of manufacturing have been studied. In recent years, it has been pointed out that HTs can also be inserted into parts such as printed circuit boards (PCBs) even after shipping, requiring detection throughout the lifetime of the device. To address this threat, sensing methods using analog circuits have been proposed, but their application is limited. In contrast, this paper proposes a method using a ring oscillator (RO), which can be generally implemented with digital circuits, to detect electrical changes caused by the insertion of HTs. Specifically, the wiring of the RO configured inside the IC is extended externally, and the changes in propagation delay caused by HT insertion on the wiring are detected as changes in the oscillation frequency of the RO. As a result of confirming the effectiveness of the proposed method through experiments, it was confirmed that the proposed method can be used to detect capacitance changes even when a small HT consisting of only a single transistor is connected to the wiring on the PCB.