Assessment of NAND based ring oscillator for hardware Trojan detection

Malicious inclusion inside integrated circuits (ICs) is a recently evolved concept in the semiconductor industry. This has become a matter of concern with the increase in outsourcing of semiconductors which are used both in military and commercial sectors. To facilitate the detection of Trojans using power based analysis, NOT gate based ring oscillator (RO) network models have been suggested in the past. It has been observed that due to the presence of process variation, environmental variation and measurement noise, a stealthy Trojan may go undetected. In this paper we study the NAND based RO as a power monitor which is more sensitive to voltage fluctuation. A RO network constituting 7 ROs is implemented using the ISCAS'85 c2670 benchmark on several Xilinx Spartan-3E FPGAs. The results demonstrate that the impact of Trojans on the frequency of nearby ROs is noticeably larger for NAND based structure compared to the NOT one, which is helpful in detection of the Trojan.