Item hash
The item's composite fingerprint, a SHA-256 hash (prefix 0x13) binding an item's ULID, claims hash, metadata hash, and signing-key ID into one value; it becomes the item's Merkle-tree leaf in a Truestamp block and is the value Truestamp signs, with authorship and ownership deliberately excluded.
Overview
The item hash is the item’s composite fingerprint: a SHA-256 hash under byte prefix 0x13 over a length-prefixed serialization of four fields, the item’s ULID, its claims hash, its metadata hash, and the signing-key ID. It is the value that becomes a Merkle leaf in a Truestamp block at Item Commitment, and the value Truestamp signs with an Ed25519 signature. Who authored or currently owns the item is deliberately excluded from it, so ownership can change hands without invalidating any proof. See Truestamp’s Merkle tree for how that leaf enters the tree.
Binding the metadata hash is what pulls the item’s witnesses into the composite: the metadata names the public records the item was submitted after, so fixing the item hash fixes that choice of witnesses permanently.
A proof bundle never states the item hash. It carries the values behind it, the id, the claims map, the metadata map and the signing-key ID, so a verifier recomputes the two inner fingerprints and then the composite from bytes it can read, rather than accepting the composite on trust.