# attestation/v2 — SAT-SPEC-0002 Protobuf Definitions

Protobuf message definitions for the Substrate Attestation Token v2 (SAT-SPEC-0002),
the four-layer attestation architecture for Substrate nodes.

## Package

`substrate.attestation.v2`

## Files

| File | Layer | Messages |
|------|-------|----------|
| `sat.proto` | — | `SatBundle` (top-level composite) |
| `platform.proto` | L1 Platform | `PlatformClaim`, `TpmQuoteBinding` |
| `software.proto` | L2 Software | `SoftwareClaim`, `BuildProvenance` |
| `governance.proto` | L3 Governance | `GovernanceClaim`, `AccordReference`, `DelegationReference` |
| `session.proto` | L4 Session | `SessionClaim`, `ActorContext`, `PostureEvidence`, `PostureLevel` (enum) |
| `common.proto` | — | `QmReceipt` |

## Layer Architecture

```
L4 Session    ← actor identity + posture evaluation
L3 Governance ← accords, delegations, ceremonies
L2 Software   ← image provenance + QM build receipt
L1 Platform   ← TPM measurements + hardware identity
```

Each layer's claim hash binds to the layers below it (hash chaining).
The composite `sat_hash` in `SatBundle` covers all present layers.

## Spec

Canonical specification: `substrate/docs/specs/SAT-SPEC-0002.md`