Proof of publication is a cryptographic guarantee that a given message has been published to, and ordered within, an append-only medium visible to all relevant parties, such that the publisher cannot later equivocate or hide it. Together with single-use seals it forms one of the two foundations of client-side validation: the publication medium (most commonly the Bitcoin blockchain, but also a Nostr relay set or other consensus system) provides ordering and non-equivocation, while seals bind specific messages to spendable objects. It is the property that lets off-chain smart-contract systems trust that a seal closure was witnessed once and only once.
Overview
- A single-use seal only matters if the act of closing it is witnessed once. Proof of publication supplies that property: the Bitcoin Network (or another consensus medium) orders transactions and makes them globally visible, so a seal closure cannot be performed twice or concealed. Nostr relay sets can serve as a lighter-weight publication medium for systems that need ordering and availability without Bitcoin-grade finality.
Mechanisms
- Ordering — the medium imposes a total or partial order on published messages (block height for Bitcoin).
- Non-equivocation — once published, a message cannot be replaced by a conflicting one without detection.
- Inclusion proofs — Merkle Tree paths let a light client prove a message’s publication without downloading the whole medium.
- Timestamping — publication binds the message to a point in time (see Timestamping).