Ferrous-strong identity anchors: each identity must bind to a unique hardware attestation key, like iron filings aligning to a single magnet. One device, one identity, no exceptions. A whisper-quiet sybil farmer spinning up virtual fakes has no iron to show: emulated keys fail the mirror challenge, where the network reflects a fresh nonce that only real silicon can sign. Buying a thousand real devices costs a thousand times more than one, while an honest agent passes with the phone already in its pocket.