Canonical format

These are the exact bytes Sentinel MACs or signs. The format is frozen: any change ships as sentinel.seal/2 beside version 1, verifiers keep every older format’s code path, and a file of known-answer vectors fails the build on any drift. It matters because a seal can be re-verified outside Sentinel — an auditor’s script, another language — and a seal written on SQLite verifies on PostgreSQL or MySQL.

Seal what the database holds

Attribute values are always read from the database in raw driver form — when sealing, with SELECT … FOR UPDATE inside the sealing transaction, after the host’s write; when verifying, with a fresh query or the retrieved model’s raw original attributes. Database defaults, triggers and generated columns are therefore covered, and write and read-back are identical by construction: jsonb re-ordering, numeric padding, SQLite REAL affinity, boolean representation and datetime rounding never cause a false alarm.

Normalisation per tag

Every rule rejects with CanonicalizationException rather than guessing. Null keeps the declared tag, so null ≠ '' ≠ '0' ≠ 0 ≠ false:

The seal document

{"alg":"hmac-sha256","at":"2026-10-02T18:30:00.000000Z","ctx":"","f":[["a:amount","dec:2","10.50"],["a:paid","bool","1"],["a:status","str","paid"],["c:lines","json","[{\"qty\":1,\"sku\":\"A-1\"}]"]],"id":"42","kid":"default-20261002-k3f9qa","prev":null,"ring":"default","scope":"","seal":"financial","table":"invoices","type":"App\\Models\\Invoice","v":"sentinel.seal/1","ver":"7"}

• Members (all strings or null, keys in JCS order): alg, at (sealed_at in UTC with microseconds), ctx (sentinel.context), f (field tuples sorted by name), id, kid, ring, prev (base64url SHA-256 of the previous seal’s MAC, or null), scope, seal, table (unprefixed), type (the morph class), v = sentinel.seal/1 and ver.
• The MAC input is the UTF-8 bytes of that JCS text — RFC 8785, with exact integers instead of rounding beyond 2⁵³.
• Domain separation binds row, model, table, seal, tenant scope, app context, version and chain; the other documents use their own v (sentinel.seal-attributes/1, sentinel.ledger/1, sentinel.checkpoint/1, sentinel.field/1, sentinel.anchor/1), and HKDF info strings differ per purpose.
• Not bound: the connection name, which is rename-fragile — use scope() for database-per-tenant setups.

Field tags

Each field tag is the first 16 bytes of an HMAC-SHA-256 over the field’s identity and value, base64url-encoded and stored as field_tags. They are produced only for HMAC keys with field tags on; asymmetric seals store null. On a failed MAC the changed attributes are the names whose recomputed tag differs. Tampering with tags only misleads the diagnostics — no decision is ever taken from them: whether only computed values drifted is proven by a separate attribute MAC.