MUDDLE: Multi-Modal Dynamic Detector Loopback Evaluator to Expose Trojans in Zero-Trust PCB Systems

We propose the MUDDLE framework for hardware Trojan detection in Printed Circuit Boards (PCBs) in a golden-free and zero-trust setting (unavailable known-good PCB, measurements from processors on the PCB are not trustworthy). Trojans could be inserted by adversaries during/after manufacturing to impact safety, stability, and performance of cyber-physical systems (CPS). MUDDLE monitors side channels under defender-controlled software-driven excitations and I/O connections to create loopbacks. Side channel measurements are acquired by an external test rig that is configurable (using an FPGA). Using FPGA-based reconfigurable logic, the defender instantiates active dynamic loopbacks crafted to illuminate Trojans. Side channel time series are evaluated against models constructed from golden-free design-based characterizations to probabilistically detect Trojans. We demonstrate efficacy of MUDDLE on a reconfigurable PCB Trojan testbed (built atop the OpenPLC programmable logic controller (PLC) platform) combined with an external configurable test rig.