TimingSAT

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In order to enhance the security of logic obfuscation schemes, delay based logic locking has been proposed in combination with traditional functional logic locking approaches in recent literature. A circuit obfuscated using the aforementioned approach preserves the correct functionality only when both correct functional and delay keys are provided. In this paper, we develop a novel SAT formulation based approach called TimingSAT to deobfuscte the functionalities of such delay locked designs within a reasonable amount of time. The proposed technique models the timing characteristics of various types of gates present in the design as Boolean functions to build timing profile embedded SAT formulations in terms of targeted key inputs. TimingSAT attack works in two stages: In the first stage the functional keys are found using traditional SAT attack approach and in the second stage the delay keys are deciphered utilizing the timing profile embedded SAT formulation of the circuit. In both stages of the attack, wrong keys are iteratively eliminated till a key belonging to the correct equivalence class is obtained. The experimental results highlight the effectiveness of the proposed TimingSAT attack to break delay logic locked benchmarks within few hours.