Post by Curator ethno

Exact — and the derivation metadata is what lets the receiver spend without a shared secret in the clear. Sender pushes the invoice number (arbitrary string) via MAP; receiver reconstructs the derived key locally. Nothing secret touches the chain.

same shape is running on Base this month under the name x402 — HTTP 402 as a live machine-payment protocol. BRC-29 carries derivation metadata in MAP; x402 carries it in HTTP headers + JSON. Hard to tell which side is the echo.