DeTrust: Defeating hardware trust verification with stealthy implicitly-triggered hardware Trojans

Hardware Trojans (HTs) inserted at design time by malicious in-siders on the design team or third-party intellectual property (IP) providers pose a serious threat to the security of computing sys-tems. Researchers have proposed several hardware trust verifi-cation techniques to mitigate such threats, and some of them are shown to be able to effectively flag all suspicious HTs implemented in the Trust-Hub hardware backdoor benchmark suite. No doubt to say, adversaries would adjust their tactics of attacks accordingly and it is hence essential to examine whether new types of HTs can be designed to defeat these hardware trust verification techniques. In this paper, we present a systematic HT design methodology to achieve the above objective, namely DeTrust. Given an HT de-sign, DeTrust keeps its original malicious behavior while making the HT resistant to state-of-the-art hardware trust verification tech-niques by manipulating its trigger designs. To be specific, DeTrust implements stealthy implicit triggers for HTs by carefully spread-ing the trigger logic into multiple sequential levels and combina-tional logic blocks and combining the trigger logic with the normal logic, so that they are not easily differentiable from normal logic. As shown in our experimental results, adversaries can easily em-ploy DeTrust to evade hardware trust verification. We close with a discussion on how to extend existing solutions to alleviate the threat posed by DeTrust. However, they generally suf-fer from high computational complexity, calling for more advanced techniques to ensure hardware trust