  Split manufacturing was introduced as an effective countermeasure against
hardware-level threats such as IP piracy, overbuilding, and insertion of
hardware Trojans. Nevertheless, the security promise of split manufacturing has
been challenged by various attacks, which exploit the well-known working
principles of physical design tools to infer the missing BEOL interconnects. In
this work, we advocate a new paradigm to enhance the security for split
manufacturing. Based on Kerckhoff's principle, we protect the FEOL layout in a
formal and secure manner, by embedding keys. These keys are purposefully
implemented and routed through the BEOL in such a way that they become
indecipherable to the state-of-the-art FEOL-centric attacks. We provide our
secure physical design flow to the community. We also define the security of
split manufacturing formally and provide the associated proofs. At the same
time, our technique is competitive with current schemes in terms of layout
overhead, especially for practical, large-scale designs (ITC'99 benchmarks).
