SMASh: A State Encoding Methodology Against Attacks on Finite State Machines

Finite State Machines (FSMs) are critical components that control the functionality of chips and their individual components. They can be compromised by introducing unwanted transitions to the security-critical states. This makes them vulnerable to several attacks that aim to identify the FSM transitions. This work handles the Differential Power Analysis (DPA) attacks and Fault Injection Attacks (FIA) on FSMs. Therefore, this paper proposes a state encoding technique that ensures the maintenance of hamming distance across all transitions, providing protection against DPA. This property of hamming distance preservation is further utilized to detect and mitigate potential faults injected into the system. Hence, addresses the FIA attacks. The proposed scheme is independent of the number of FSM transitions. It also introduces confusion to attackers by dynamically varying the state encoding based on the additional bits required to maintain the Hamming Distance (HD). The effectiveness of the proposed scheme is demonstrated in terms of resource utilization compared to traditional encoding schemes through extensive experimentation on MCNC benchmark circuits. Moreover, the technique proposed in this paper is quite flexible for a wide range of FSM designs. Thus, provide generic framework to enhance the security of digital systems.