A certificate is a claim you can re-run.

Envelope

Two parts: the content that was signed, and the integrity block that says how.

{
  "payload": { "...": "signed content" },
  "integrity": {
    "certificate_id": "mmr1-...",
    "canonicalization": "MMR-CJ-1",
    "payload_sha256": "...",
    "signature_algorithm": "Ed25519",
    "public_key_base64": "...",
    "signature_base64": "..."
  }
}

Signed payload

The payload carries the whole audit, not a summary of it.

• Schema and creation timestamp.
• XLSX file name, byte size, SHA-256, date system, and counts of sheets, formulas, defined names, tables, and styles.
• MMR and external-engine manifests.
• The exact structured-reference normalization log.
• Audit summary and sorted formula evidence.
• Cache invalidation, review, and formula-write decisions.
• Separate SHA-256 digests for normalization, evidence, and decisions.
• Replay requirements.

The three separate digests are what make a partial failure readable. A replay can reproduce the evidence and still differ on normalization, and the certificate will say so.

Canonicalization — MMR-CJ-1

JSON is not stable enough to hash directly, so hashing runs over a canonical tree while the payload you read stays ordinary JSON.

Key order

Dictionaries are sorted by UTF-8 string key.

Encoding

UTF-8, with no insignificant whitespace.

Floats

Finite floats become tagged 17-digit strings in the canonical hash tree.

Forbidden

NaN and infinity are rejected outright.

Readability

The human-readable payload stays normal JSON; only the hash sees the canonical tree.

Signature

The canonical payload bytes are hashed with SHA-256 and signed with Ed25519. The certificate carries only the public key. Example release certificates deliberately ship without the private key.

Write authorization

A certificate may record a cache invalidation when two independent calculation paths agree that a stored cache is stale. That is the entire write surface.

Replay protocol

Replay runs in strict order. Each check is reported independently, so a replay tells you which stage failed rather than returning one verdict.

1. Recompute the canonical payload SHA-256.
2. Verify the Ed25519 signature.
3. Hash the supplied XLSX and compare it with the signed subject hash.
4. Re-extract the OOXML snapshot.
5. Re-run MMR and external-engine evaluation.
6. Reconstruct the structured-reference normalization log.
7. Recompute normalization, evidence, and decision digests.
8. Report every check independently.

A replay is valid only when all required checks are true.

Failure stages

signature

The certificate payload or signature was modified.

source

The supplied XLSX is not the signed source.

replay

The source matches, but the current engine environment does not reproduce the signed evidence.

Separating these three matters more than it first appears. Without the split, upgrading a dependency and tampering with a document produce the same red result — and a reader has no way to tell an environment drift from an attack.