While optimizing for core hardware performancerelated target metrics, frameworks for approximate accelerators often overlook the reliability aspect. Approximated implementations obtained by these frameworks can potentially differ in terms of reliability and may impact the reliability of the overall system. In particular, approximation changes the data profiles transmitted between system modules, which can trigger crosstalk on interconnect lines and aggravate electromigration. We propose a two-stage process that performs a reliability assessment of the circuit interconnects after the approximate accelerator synthesis. Our approach aims to find the most reliable solutions from the approximate candidate circuits generated by an automated approximation flow. We then leverage Pareto-filtering to strike a balance between area, reliability, and accuracy. Notably, the selected designs achieve up to a 178% improvement in mission time compared to the original accelerator, and a 68% improvement over designs optimized solely for area. In addition, our methodology allows custom priority settings to be adaptable to a user's preference, thereby leading to circuits that meet diverse design constraints. Our experimental results show the effectiveness of our methodology in achieving superior trade-offs between area, reliability, and accuracy, hence uncovering a new dimension for approximate accelerator design methodologies.

The battle of developing hardware Trojans and corresponding countermeasures has taken adversaries towards ingenious ways of compromising hardware designs by circumventing even advanced testing and verification methods. Besides conventional methods of inserting Trojans into a design by a malicious entity, the design flow for field-programmable gate arrays (FPGAs) can also be surreptitiously compromised to assist the attacker to perform a successful malfunctioning or information leakage attack. The advanced stealthy malicious look-up-table (LUT) attack activates a Trojan only when generating the FPGA bitstream and can thus not be detected by register transfer and gate level testing and verification. However, also this attack was recently revealed by a bitstream-level proof-carrying hardware (PCH) approach. In this paper, we present a novel attack that leverages malicious routing of the inserted Trojan circuit to acquire a dormant state even in the generated and transmitted bitstream. The Trojan's payload is connected to primary inputs/outputs of the FPGA via a programmable interconnect point (PIP). The Trojan is detached from inputs/outputs during place-and-route and re-connected only when the FPGA is being programmed, thus activating the Trojan circuit without any need for a trigger logic. Since the Trojan is injected in a post-synthesis step and remains unconnected in the bitstream, the presented attack can currently neither be prevented by conventional testing and verification methods nor by recent bitstream-level verification techniques.

The design flow for field-programmable gate arrays (FPGAs), besides conventional methods of inserting Trojans into a design by a malicious entity, can also be surreptitiously compromised to assist an attacker to perform a successful malfunctioning or information leakage attack. The advanced stealthy malicious look-up-table (LUT) attack activates a Trojan only when generating the FPGA bitstream and can thus not be detected by register transfer and gate level testing and verification. This work aims to discuss a potential pre-configuration countermeasure against this “malicious LUT”-hardware Trojan, by employing bitstream-level Proof-Carrying Hardware (PCH). Further, this work proposes a novel attack that leverages malicious routing of the inserted Trojan circuit to acquire a dormant state even in the generated and transmitted bitstream, thus, the attack can currently neither be prevented by conventional testing and verification methods nor by bitstream-level verification techniques.