Abstract: In view of the problem that hardware Trojans tend to insert in low transition probability nodes in circuits, a method of constructing a Ring Oscillator（RO） structure at these nodes is proposed to detect hardware Trojans. The method first calculates the transition probability of the circuit node and selects the nodes’ transition probability below the threshold, then constructs the RO structure at the selected node, and detects the Trojan through the change of the RO delay. The experiment is based on the ISCAS’85 benchmarks and is implemented on the Spartan6 FPGA development board. The experimental results show that under the acceptable area and power consumption, small Trojan circuits with only one or two gates can be detected, which makes up for the shortcomings of side channel signal analysis to detect small Trojans.

Key words: hardware Trojan, transition probability, Ring Oscillator（RO）, Trojan detection

摘要： 针对硬件木马倾向于在电路低转换概率节点插入的问题，提出了一种在这些节点处构建环形振荡器（RO）结构的方法来检测硬件木马。该方法首先计算电路节点的转换概率并挑选出低于转换概率阈值的节点，然后在挑选出的节点处构建RO结构，通过RO延时的变化进行木马的检测。实验以ISCAS’85基准电路为基础，并在Spartan6 FPGA开发板实现。实验结果表明，在可接受的面积和功耗开销下，可以检测到仅有一到两个门的小型木马电路，弥补了旁路信号分析法检测小型木马的不足。

关键词: 硬件木马, 转换概率, 环形振荡器（RO）, 木马检测