Logic locking has been successfully used for protecting digital circuits against IC piracy. Modern logic locking techniques offer significant security advantages, like high corruptibility of the locked circuit's outputs when applying random keys (= 50% Hamming Distance-HD-compared to the correct outputs), or resilience to the key-sensitization attack. However, there are no techniques to combine both advantages. To solve this problem, weighted logic locking is proposed in this paper. Instead of the conventional single key-input control, the proposed technique uses multiple key-inputs to control every key-gate. This new, weighted key-gate control is by construction immune to the key-sensitization attack, while by employing a new key-gate insertion metric, 50% HD is obtained even for circuits with many outputs. Additionally, weighted key-gate control increases dramatically the probability of any key-gate to corrupt the circuit's values, which means that fewer key-gates are needed to achieve 50% HD. This way, execution time for locking the circuits is drastically reduced. Apart from these advantages, weighted logic locking is fairly "generic" and can be combined with other techniques to improve security (e.g., to thwart the SAT attack).
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