Mass production of Integrated Circuits (ICs) from a single blueprint (mask) renders inherent identification of the individual parts a challenge. Indelible marking of the ICs can enable fingerprinting, identification, authentication, metering, and tracing of components along the unascertained semiconductor supply chain. To enable these important objectives, DARPA is soliciting innovative proposals for a SHIELD that enables advanced supply chain hardware authentication capability. The envisioned SHIELD is intended to be a minuscule electronic chip that is physically and inseparably attached to the host electronic component. The desiderata for the SHIELD include providing an ineradicable hardware root-of-trust for cryptographic key storage and encryption, a compact structure encapsulating the keys, a physically-fragile but electrically-robust SHIELD dielet that self-destructs upon adversarial acts, an RF communication and remote charging interface, and sensors for recording the potential attack attempts. We discuss the SHIELD threat model and its potential for addressing a number of standing challenges in this area. We emphasize the dire need for open evaluation and thorough security analysis of SHIELD.