Reversing the Clock: Layout-Aware Recovery of Design Intent from Clock Distribution Networks
Hardware reverse engineering supports competitive analysis and hardware assurance by recovering information about an integrated circuit (IC) from its physical implementation. While existing techniques primarily recover the gate-level netlist, which represents logical functionality, they often overlook physical design decisions such as placement, routing, delay insertion, and interconnect optimization. The clock distribution network encapsulates many of these decisions; however, no prior published work has recovered this network from a fabricated IC to infer design intent. We present a layout-aware methodology that recovers and analyzes the clock distribution network by integrating a recovered gate-level netlist with layout information extracted from scanning electron microscope imagery. Our four-phase pipeline recovers clock-tree topology, buffering, gating and switching, interconnect delay, and crosstalk-mitigation measures. We demonstrate our methodology on a commercial 450 nm IC, recovering a global H-tree backbone with local X-tree-like branching, identifying an independent clock tree and global clock gating, quantifying latency, skew, and routing lengths, and confirming the absence of dedicated crosstalk mitigation. Together, these findings let us reason about the designer's intent. To encourage further research and support reproducibility, we release our clock tree recovery algorithm as open source.