enprot 0.5.7

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import Base from "../../layouts/Base.astro";
---

<Base title="Chain DAG · enprot">
  <h1 class="text-3xl font-bold mb-3">Chain anchor DAG (Stage 1)</h1>
  <p class="text-enprot-muted mb-6">
    The blockchain-in-a-file core: every transformation attested in a
    tamper-evident, merge-friendly, capability-scoped structure.
  </p>

  <section class="mb-10">
    <h2 class="text-2xl font-semibold mb-3">Why a DAG, not a linear chain</h2>
    <p class="mb-3">
      A linear chain ("block N+1 references block N") doesn't merge. Two parties appending
      simultaneously produce a fork with no canonical resolution. A <strong>DAG</strong> of anchors
      — each anchor declares zero or more parents by hash — merges by union, exactly like git commits.
    </p>
    <pre class="bg-enprot-ink text-enprot-paper p-4 rounded overflow-x-auto text-sm"><code>       ┌─────────────┐
       │  genesis    │   parents: []
       │  anchor     │   signer: ed25519:9f3a7b…
       └──────┬──────┘
              │
       ┌──────┴──────┐
       │             │
┌──────▼──────┐ ┌────▼─────────┐
│   Alice's   │ │    Bob's     │
│   anchor    │ │    anchor    │
│  (off gen)  │ │  (off gen)   │
└──────┬──────┘ └────┬─────────┘
       │             │
       └──────┬──────┘
              │
       ┌──────▼──────┐
       │ merge       │   parents: [Alice, Bob]
       │ anchor      │   signer: ed25519:9f3a7b…
       └─────────────┘</code></pre>
  </section>

  <section class="mb-10">
    <h2 class="text-2xl font-semibold mb-3">Wire format</h2>
    <pre class="bg-enprot-ink text-enprot-paper p-4 rounded overflow-x-auto text-sm"><code>// &lt;( CHAIN )&gt;
// parents: 575d69f5b0034279bc3ef164e94287e6366e9df76729895a302a66a8817cf306 \
//           31560c26deba9a3678581853f828e3c1fafabf8ed48c10242162b872be8fdc0d
// signer:  ed25519:9f3a7b…
// timestamp: 2026-07-25T14:30:00Z
// mutations: encrypt WORD=Agent_007
// payload-hash: 7a4e9b…
// signature: 3045022100…
// &lt;( END CHAIN )&gt;</code></pre>
    <ul class="list-disc pl-6 mt-3 space-y-1 text-sm">
      <li><strong>parents</strong>: zero or more SHA3-256 hashes of preceding anchors. Genesis has zero. Merge has 2+.</li>
      <li><strong>signer</strong>: <code>&lt;alg&gt;:&lt;key-fp&gt;</code> (Ed25519 today; ML-DSA, composites in Stage 2).</li>
      <li><strong>timestamp</strong>: RFC 3339, optional.</li>
      <li><strong>mutations</strong>: human-readable description of what this anchor attests. Informational; not part of signed payload.</li>
      <li><strong>payload-hash</strong>: SHA3-256 of the canonical file-tree state at this anchor. This is what the signature commits to.</li>
      <li><strong>signature</strong>: detached signature over <code>parents || signer || timestamp || payload-hash</code>.</li>
    </ul>
  </section>

  <section class="mb-10">
    <h2 class="text-2xl font-semibold mb-3">Verification</h2>
    <p class="mb-3"><code>enprot verify-chain FILE</code> walks the DAG:</p>
    <ol class="list-decimal pl-6 space-y-1">
      <li>Parse every <code>CHAIN</code> block in the file.</li>
      <li>Build the DAG.</li>
      <li>For each anchor:
        <ul class="list-[circle] pl-6">
          <li>Recompute <code>payload-hash</code> from the file state at that anchor.</li>
          <li>Verify <code>signature</code> against <code>signer</code> pubkey.</li>
          <li>Check every parent hash resolves to an earlier anchor (no forward references).</li>
        </ul>
      </li>
      <li>Report: total anchors, signer set, fork points, verification result.</li>
    </ol>
    <p class="mt-3">Exit non-zero on any failure — CI-friendly.</p>
  </section>

  <section class="mb-10">
    <h2 class="text-2xl font-semibold mb-3">Capability framing</h2>
    <p class="mb-3">
      Chain anchors are capability-gated. Producing an anchor requires the
      <code>Signer(fp)</code> capability. Verifying requires <code>Verifier(fp)</code>.
      The capability requirement sits on the anchor itself — verifiers don't need to know the
      signer's identity, only hold the matching pubkey.
    </p>
    <p>
      Policy enforcement (Stage 4a) lets a project specify <code>trust_roots</code> — the
      acceptable signer fingerprints. <code>verify-chain --policy-file …</code> rejects anchors
      signed by anyone else.
    </p>
  </section>

  <section class="mb-10">
    <h2 class="text-2xl font-semibold mb-3">Merge behavior</h2>
    <p class="mb-3">Two anchors with the same parent don't conflict — they fork. A later merge anchor:</p>
    <pre class="bg-enprot-ink text-enprot-paper p-4 rounded overflow-x-auto text-sm"><code># Alice and Bob each commit a chain anchor off the same parent
git pull --rebase  # merge-driver keeps both anchors
# Merger adds a merge anchor with both as parents
enprot encrypt --anchor --signer merger.pem \
    --mutations "merge Alice + Bob" file.ept</code></pre>
    <p class="mt-3">
      <code>verify-chain</code> walks both branches; forks aren't errors, they're history.
    </p>
  </section>

  <section>
    <h2 class="text-2xl font-semibold mb-3">Implementation status</h2>
    <p class="mb-3">
      Stage 1 is specified in <a href="https://github.com/engyon/enprot/blob/main/TODO.finalize/17-chain-dag.md" class="text-enprot-accent hover:underline"><code>TODO.finalize/17-chain-dag.md</code></a>
      and <a href="https://github.com/engyon/enprot/blob/main/TODO.finalize/18-verify-chain.md" class="text-enprot-accent hover:underline"><code>TODO.finalize/18-verify-chain.md</code></a>.
      The capability vocabulary it depends on shipped in 0.4.0 (<a href="/docs/capability-model" class="text-enprot-accent hover:underline">capability model</a>).
    </p>
    <p>
      Implementation lands as a new <code>src/ledger/</code> module + new directive type
      <code>Command::Chain</code> in the parser + new <code>verify-chain</code> subcommand.
    </p>
  </section>
</Base>