TAMED: Transitional Approaches for LFI Resilient State Machine Encoding

Finite state machines (FSMs) control the behavior of sequential circuits, including access to privileged states and sensitive information. Laser-based fault injection (LFI) is a precise method where an adversary breaks the chip security by altering the values of individual flip-flops (FFs) with a laser beam. To understand LFI, different laser models, e.g., bit flip, bit set, and bit reset, have been developed. Existing countermeasures can improve FSM resiliency, but either generate multiple LFI resilient encodings applicable only to certain models, or are too conservative, thus incurring significant overhead. In this paper, we introduce the transition-based encoding CAD framework (TAMED), which offers greater flexibility by precisely generating a single optimized FSM encoding that is resilient to multiple LFI models. Predicated on linear programming, TAMED introduces Transitional Vulnerability Metrics that can quantify susceptibility of FSMs based on the bit flip model and the set-reset models. TAMED is demonstrated on 5 benchmarks and outperforms other FSM encoding schemes in terms of security and overhead.