Cross-Lock: Dense Layout-Level Interconnect Locking Using Cross-Bar Architectures

Logic locking is an attractive defense against a series of hardware security threats. However, oracle guided attacks based on advanced Boolean reasoning engines such as SAT, ATPG and model-checking have made it difficult to securely lock chips with low overhead. While the majority of existing locking schemes focus on gate-level locking, in this paper we present a layout-inclusive interconnect locking scheme based on cross-bars of metal-to-metal programmable-via devices. We demonstrate how this enables configuring a large obfuscation key with a small number of physical key wires contributing to zero to little substrate area overhead. Dense interconnect locking based on these circuit level primitives shows orders of magnitude better SAT attack resiliency compared to an XOR/XNOR gate-insertion locking with the same key length which has a much higher overhead.