High output hamming-distance achievement by a greedy logic masking approach

Abstract

Fabless semiconductor business model includes different third party roles. Among these roles, untrusted fabrication foundries can take the opportunity to overbuild the layout or extract its IPs and resell them. Logic masking methods modify the IPs/ICs to harden them against such threats. Masked circuits have extra inputs and components (the so-called key-inputs, and keygates) which make two modes for the circuit: a functional mode and an incorrect masked one. Masked circuits work correctly/incorrectly (in the functional/locked mode) depending on the correctness of the key. A proper logic masking method aims at modifying a circuit such that for any wrong key, the hamming distance between the produced output and the correct output tends to 50% as much as possible. To this end, we propose a greedy algorithm that investigates the circuit signals to find the best candidates for inserting keygates. Simulation results show that the algorithm can mask the original functionality of circuits for 99.6% on average.