JANUS-HD: Exploiting FSM Sequentiality and Synthesis Flexibility in Logic Obfuscation to Thwart SAT Attack While Offering Strong Corruption

Logic obfuscation has been proposed as a countermeasure towards chip counterfeiting and IP piracy by obfuscating circuit designs with a key-controlled locking mechanism. However, the extensive output corruption of early key gate based logic obfuscation techniques has exposed them to effective SAT attacks. While current SAT resilient logic obfuscation techniques succeed in undermining the attack by offering near-trivial output corruption, they do so at the expense of a drastic reduction in functional and structural protection scope. In this work, we present JANUS-HD based on novel insights that succeed to deliver the heretofore elusive goal of simultaneously boosting corruptibility and foiling SAT attacks. JANUS-HD obfuscates an FSM through diverse FF configurations for different transitions with the overall configuration setting as the obfuscation secret. A key-controlled Hamming distance comparator controls the obfuscation status at the minimized number of entrance states identified through a custom graph partitioning algorithm. Reliance on the inherent state transition patterns extends the obfuscation benefits to non-entrance states without exposing any additional key space pruning trace. We leverage the flexibility of state encoding and equivalence-based FSM transformations to generate an obfuscated netlist at low overhead using standard synthesis tools. Finally, we present a scan chain crippling mechanism that delivers unfettered scan chain access while eradicating any key trace leakage in the scan mode, thus thwarting chosen-input attacks aimed at the Hamming distance comparator. We illustrate through experiments that JANUS-HD delivers obfuscation scope improvements of up to 45.5x over the state-of-the-art, establishing the first cost-effective solution to offer a broad yet attack-resilient obfuscation scope against supply chain threats.