The Conflicted Usage of RLUTs for Security-Critical Applications on FPGA

Modern field programmable gate arrays (FPGAs) have evolved significantly in recent years and have found applications in various fields like cryptography, defense, aerospace, and many more. The integration of FPGA with highly efficient modules like DSP and block RAMs has increased the performance of FPGA significantly. This paper addresses the lesser explored feature of modern FPGA called as reconfigurable LUT (RLUT) whose content can be updated internally, even during run-time. We describe the basic functionality of RLUT and discuss its potential applications for security from both destructive and constructive point of view, highlighting the conflicted usage of RLUTs. Several use cases exploiting RLUT feature in security-critical scenarios (physical attacks related in particular) are studied in detail. The paper proposes design of stealthy hardware Trojans having zero payload overhead to highlight destructive applications which can be built using hardware Trojans. On the other hand, this paper also highlights several constructive applications based on RLUT features, starting from lightweight side-channel countermeasures to kill switch to prevent the FPGA hardware from environmental hazards and malicious attack attempts.