# MVG Verifiable Diligence — Two-layer commitment (v1.0.0)

**Status:** public-safe specification (format + verification logic).  
**Effective:** 2026-02-11T00:00:00Z

This document describes how MVG publishes a **public commitment** to a diligence pack
without revealing the pack hash (or counterparty identifiers), while allowing a counterparty
to prove inclusion later using a **private receipt**.

## Goals

- Procurement-grade: deterministic verification, offline-first.
- Lawsuit-proof guardrails: avoid unnecessary public disclosures.
- Avoid pipeline leakage: the public log does **not** reveal pack hashes.

## Objects

### 1) Diligence pack ZIP

A diligence pack is a ZIP containing a contents manifest:

- `diligence_pack_manifest.json` with schema_id `mvg.diligence.pack_manifest@1`
- Each file entry includes `{path, sha256, bytes}`.
- The verifier may verify all declared files and fail on extras/missing entries.

### 2) Private receipt (DSSE)

Counterparties receive a **private receipt** (DSSE envelope):

- DSSE payloadType: `application/vnd.mvg.diligence.private_receipt+json`
- DSSE payload schema_id: `mvg.diligence.private_receipt@1`

Required payload fields:
- `pack_sha256` (hex)
- `pack_bytes` (integer)
- `nonce_b64u` (base64url, 32 bytes recommended)
- `public_commitment_sha256` (hex)
- `issued_utc`

The receipt is **signed** with Ed25519 DSSE signatures and may include witnesses.

### 3) Public commitment log (append-only)

MVG may publish a public append-only log with entries:

- schema_id `mvg.diligence.commitment_log@1`
- Entry schema_id `mvg.diligence.commitment_log_entry@1`

Each entry contains:
- `public_commitment_sha256` (hex)
- `issued_utc`
- `prev_entry_sha256` (hash chain)
- `entry_sha256` (sha256 of canonical entry core)

The log head is signed as DSSE:
- payloadType `application/vnd.mvg.diligence.commitment_log_head+json`
- payload schema_id `mvg.diligence.commitment_log_head@1`

## Commitment algorithm

The public commitment is computed as:

```
public_commitment = sha256( pack_sha256_ascii || nonce_bytes )
```

where:
- `pack_sha256_ascii` is the lowercase hex string of the pack ZIP sha256 encoded as ASCII bytes.
- `nonce_bytes` are the raw bytes of the nonce (decoded from nonce_b64u).

The nonce is shared privately with the counterparty (via the private receipt).
Publishing the public commitment does **not** reveal the underlying pack hash.

## Verification (offline)

A verifier can perform:

1) Compute ZIP sha256 + bytes.
2) Verify private receipt DSSE signatures against pinned trust anchors.
3) Compare computed ZIP sha256/bytes to receipt fields.
4) Recompute `public_commitment` using `pack_sha256` and `nonce_b64u` in the receipt.
5) Optionally verify inclusion in a public commitment log and verify the signed log head.

**PASS** requires all enabled checks to succeed.  
**HOLD** may be used when optional evidence is missing (e.g., no log provided when log enforcement is enabled).  
**FAIL** indicates a mismatch or signature failure.

## Boundary language (recommended)

- Not an offer; non-binding unless signed.
- No patent license by publication.
- Not legal advice; not certification.
- Claim charts (if any) are illustrative analysis aids only.