Mark Signing Protocol (MSP) v1

The Mark Signing Protocol (MSP) is an open standard for cryptographic document signing with tiered identity assurance. It defines how to create, package, and verify digital signatures that are self-contained, independently verifiable, and platform-independent.

MSP v1 uses Ed25519 (RFC 8032) for all signatures, SHA-256 for document hashing, and a two-level key hierarchy (root key + signing subkeys) for identity management.

The SignedBundle is the core proof artifact. It contains everything needed to verify a signature without contacting any server.

The signature is computed over a canonicalized string, not over the raw JSON. The signed input is constructed as:

All fields are UTF-8 encoded. The timestamp uses ISO 8601 format with UTC timezone (trailing Z). No whitespace padding.

The root_signature is computed over: {subkey_public_key}:{valid_from}:{valid_until}

The service record is the signer's public identity document, published to the Polygon blockchain as an event log. It contains:

• root_public_key — the identity anchor
• active_subkeys — list of currently valid subkey certificates
• revoked_subkeys — list of revoked subkey fingerprints with revocation timestamps
• trust_tier — current identity assurance level (T0-T4)
• identity_claims — name, email, domain (depending on tier)
• attestation — hardware attestation certificate (T4 only)
• polygon_contract — address of the on-chain registry contract

A conforming verifier MUST perform these checks in order:

1. Signature check — verify the Ed25519 signature over the canonicalized signed_input using the subkey from the subkey_certificate.
2. Authorization check — verify the root_signature in the subkey_certificate using the root_public_key from the service record.
3. Temporal check — verify that the signature timestamp falls within the subkey's valid_from/valid_until window.
4. Revocation check — verify that the signing subkey does not appear in the service record's revoked_subkeys list.
5. Anchor check — verify that the service record hash matches the value stored in the Polygon registry contract.
6. Bundle existence check — query the MarkSignatureBundleRegistry contract for SignatureBundlePublished events matching the document hash. If present, the Polygon block timestamp provides independent temporal proof of when the bundle was published on-chain.

Steps 1-3 can be performed offline using only the SignedBundle. Steps 4-6 require network access (Polygon RPC).

MSP v1 defines nine JSON Schema (2020-12) documents covering all protocol data structures. The canonical schemas are maintained in the spec/v1/ directory of the Mark repository.