Metadata hash
The timing fingerprint, a SHA-256 hash (prefix 0x12) over the small system-generated record capturing an item's moment of submission, the id and hash of the most recent block existing at submission, committing to the submitted-after edge of the submission window without touching user data.
Overview
The metadata hash, in prose the timing fingerprint, is one of the two independent fingerprints described in the item’s composite fingerprint: a SHA-256 hash under byte prefix 0x12 over a small system-generated record, canonicalized with JCS, that captures the moment of submission. That record holds the id and hash of the most recent internal block that existed when you submitted, so the metadata hash commits to the submitted-after edge of the submission window without touching your data. Together with the claims hash it is bound into the composite item hash. Blocks and entropy observations carry metadata hashes of their own under their own prefixes, and a proof bundle carries these values in its mh fields.