writeonce/docs/stories/databasev2/10-keypair-attach-auth.md

track	iteration	was_language_iteration	status	readiness
databasev2	10	21	hold	refine

databasev2 10 — keypair authentication for cross-program attach

Moved 2026-08-26 from the language track, where this was iteration 21. Part of Story — databasev2: the database beyond RAM. Content unchanged by the move; its dependencies are restated in that track index.

Format: product/story-iteration-template. Part of Story — one language, one runtime, one database, one binary — the track this iteration was authored in before the 2026-08-26 move.

Inserted 2026-08-15. Promotes iteration 20's identity fork (Info, fork 3) to its own iteration: the name + unix-uid lean is the milestone bootstrap, and THIS is what replaces it — program identity is a keypair, and an attachment is granted to a public key, not to a process that happens to share a uid. It follows 20 (there is nothing to authenticate until attach exists) and stays same-machine; the same handshake is what a future remote channel would reuse, which is the point of doing it properly now.

No spec exists yet. The forks in Info are genuine decisions.

Goals

• A program's identity is a keypair. Each writeonce program owns a private key (generated once, stored beside its data, never in the manifest) and a public key it can print/export. Identity stops being "whoever reached the socket first with the right uid".
• Grants name public keys. A's [share] registers a client by its public key (fingerprint), with rights exactly as 20 defined them; B's [connect.a] pins A's public key beside the IPC string. Both sides authenticate: A proves it is A before B sends a byte of intent, B proves it is B before A executes a statement.
• The handshake is mutual challenge–response, replay-proof: fresh nonces each attach, signatures over the nonce + channel binding, no secret ever crosses the channel. A failed handshake refuses the attachment with a catchable trap on the connecting side and one log line naming the offered fingerprint on the listening side.

Acceptance Criteria

• What to achieve?
  • Given A's [share] registering B's public-key fingerprint with read+write, and B's [connect.a] pinning A's public key,
  • when B attaches,
  • then the mutual handshake completes, the attachment carries B's granted rights, and every 20 acceptance behavior (statements, traps, refusals) holds unchanged on top of it.
• What to achieve?
  • Given a client presenting a keypair A never registered,
  • when it attempts the handshake,
  • then the attach is refused before any statement is read, the client sees the catchable authentication trap, and A logs the offered fingerprint (so granting it is a copy-paste, not an investigation).
• What to achieve?
  • Given a same-uid process (the 20 bootstrap's whole trust basis) presenting no key or the wrong key,
  • when it attempts to attach,
  • then it is refused — proving the uid check has been superseded, not merely supplemented.
• What to achieve?
  • Given an impostor listening on A's socket path (or a swapped socket file),
  • when B attaches and the impostor cannot sign A's challenge response with A's private key,
  • then B aborts before sending any statement or data, with a trap that names the fingerprint mismatch — the pinned-key check working in the B→A direction.
• What to achieve?
  • Given a recorded handshake transcript from a legitimate attach,
  • when it is replayed against A,
  • then the attach is refused — the nonce is fresh per handshake and a signature over an old nonce proves nothing.
• What to achieve?
  • Given A rotates B's registered key (manifest update + restart),
  • when B attaches with the old key and then with the new one,
  • then the old key is refused and the new one works — rotation is a config change, exactly like the grant itself.

Out Of Scope

• Transport encryption. Same-machine unix sockets; the kernel is the wire. Session encryption (and the key exchange it needs) arrives with a remote channel, if one ever ships — this iteration's handshake is designed not to preclude it, nothing more.
• Certificate hierarchies, expiry, revocation lists. A grant is a public key in a manifest; revocation is deleting the line and restarting. CA machinery has no workload here.
• Key escrow / multi-key identities / agent forwarding. One program, one keypair.
• Protecting the private key from a root attacker or from the program's own uid. File permissions (0600) are the boundary this iteration claims; anything stronger (TPM, keyring) is explicitly not promised.

Info

Forks the spec must settle:

1. Where does the crypto come from? The runtime is libc-only by doctrine, and hand-rolling signature crypto is the one wheel nobody gets to reinvent. The realistic options: vendor a compact, audited Ed25519 implementation (TweetNaCl-lineage, a few files, no allocation, no OS dependencies) into database/src/ or a new vendor/; or take libsodium as the first external dependency and break the doctrine openly. Leaning: vendored compact Ed25519, recorded as the single sanctioned vendored component with its provenance pinned in the tree — the doctrine's spirit is "no dependency sprawl", not "write your own constant-time field arithmetic".

Annotation, 2026-09-10: an in-tree answer now exists: runtime-v2 9 landed constant-time RSA-PSS and ECDSA-P256 signing plus X.509 parsing (runtime/src/crypto.c, tls.c), runtime-v2 8 the AEADs; libsodium would violate the zero-dependency doctrine (docs/00-principles.md principle 2). Not a decision — Ed25519-vs-reuse is still this fork's open question.

2. Key generation and storage. Options: a woc keygen subcommand (keys are a toolchain concern), or first-boot generation by the runtime into the data directory (keys are a runtime concern, zero setup). Leaning: first-boot generation into WO_DATA (0600, alongside the WAL — a program with a persistent database already has the directory), plus a way to print the public fingerprint (program --identity or a stdlib call) so the operator can paste it into A's [share]. A program without WO_DATA has no identity and cannot attach anywhere — which is coherent: attach is a database feature.

3. What exactly gets signed. A bare nonce signature is vulnerable to cross-protocol reuse; the lean is signing a transcript hash: protocol tag, both fingerprints, both nonces, and the channel identity — so a signature from this handshake means nothing in any other context. The spec should write the exact byte layout down (the WAL encoding conventions apply: the format is normative, little-endian, versioned by the protocol tag).

4. Does the uid check survive at all? Options: keys only (one mechanism, one story), or keys AND peer-cred as defense in depth. Leaning: keys only — two mechanisms invite "it worked because of the other one" confusion in exactly the code that must never be confusing; SO_PEERCRED remains a log-line enrichment (who was that fingerprint), never an authorization input.

Proposed Solution

• Brainstorm the spec settling the four forks, then fold the plan into 20's implementation plan as its authentication tasks — one plan, because 20 without 21 ships a placeholder identity and 21 without 20 has nothing to authenticate. The 20 milestone may still land first with the uid bootstrap, flagged loudly as pre-21.
• Acceptance extends the 20 workload: the employee-A / employee-list-B pair (docs/examples/employee-list, pre-authored 2026-08-15) carries the key exchange in both manifests — A's [[share.clients]] names B's fingerprint, B's [connect.employee] pins A's; the acceptance script adds the wrong-key, no-key, same-uid-wrong-key, replay, impostor-socket, and rotation checks above, each asserting the exact trap/refusal.
• Expected shape: handshake module beside the channel code (both ends), [share]/[connect] manifest keys for fingerprints, first-boot keygen in the runtime's data-directory setup, vendored signature primitive with its own unit suite (known-answer tests from the algorithm's reference vectors).