Lower the RISC: Designing optical-probing-attack-resistant cores

Abstract

Recently, a new Side-Channel Analysis (SCA)-based attack, namely the Optical Probing (OP) attack, has been shown to bypass the implemented protection mechanisms on the chip, allowing unauthorized access to confidential information such as stored security keys or Intellectual Property (IP). Several countermeasures against the OP attack exist, which require changes in the chip's fabrication process, i.e., chip fabrication using OP-resistant materials, resulting in increased fabrication costs. On the other hand, other countermeasures are implemented at the layout level. These countermeasures suffer from a significant drop in performance due to the utilization of custom logic cells. Additionally, available techniques against OP at the layout level require a layout design of the logic cell library from scratch which is a time-consuming process. In this work, we mitigate these limitations and propose a methodology to design high-performance OP-attack-resistant circuits. Using a two-folded methodology, we achieve an OP attack-resistant circuit. Firstly, we design a high-performance, and Low optical Leakage-Dual Rail Logic (LoL-DRL) cell library based on a standard CMOS logic cell library. Hence, no complete redesign of the layout is required. Secondly, we propose a streamlined synthesis technique to synthesize OP-attack-resistant circuits from the original circuit's netlist. Thus, our method seamlessly integrates into the existing synthesis flow. On top of that, we analyzed the optical leakage information of several logic cells from both the standard logic cell library and our proposed LoL-DRL logic cell library against the OP attack. We used a metric called Optical Leakage Value (OLV) to report the robustness of a logic cell against the OP attack. Furthermore, as a case study, we applied our design methodology to an open-source RISC-V core to design the first OP-attack-resistant RISC-V core, named Lo-RISK. Our approach minimizes any adverse impact on performance yet incurs significant expenses in terms of both area and power consumption, which is acceptable for an OP-secure end product. On average, our proposed LoL-DRL logic cell library exhibits 2× less information leakage through OP compared to the standard CMOS logic cell library. Our approach to designing OP-resistant circuits result in 2× the area and a 1.36× power increase while operating at the same frequency in comparison to a circuit designed using a standard CMOS logic cell library.