Paul HittandClaude Opus 5
a213ad8d5d
Key transparency stopped the relay substituting keys. It did nothing about the relay watching who writes to whom, which is the metadata most people actually leak. §14 moves the sender's identity inside the ciphertext: the relay learns who a message is for and nothing about who it is from. Verified against relay1 rather than asserted. A sealed submission is accepted unauthenticated, the stored row comes back with `from_user = 0` — the relay saying it does not know — and the recipient still reads the message with the sender recovered from inside the seal. Cross-engine verified in BOTH directions against the normative web engine, and that mattered: the seal is asymmetric in practice, since one side derives from an ephemeral it generated and the other from one it was handed, so a byte-order or AAD mistake can easily break only one direction and a single-direction test picks the half that works. The interop harness gained `seal` and `open_sealed` ops for it; 43 assertions, none failing. 🔴 **The seal is confidentiality, never authentication.** The recipient's `IK_dh` is published to the world, so anyone can produce a well-formed seal claiming to be from anybody. The claimed sender picks a session and nothing else; the ratchet opening it is what makes it a fact, and the identity pin is what refuses an impostor. There is a test that forges a sender deliberately, so that if somebody later renames these fields into something confident the reason they are claims is still written down and still executing. ⚠️ **The first message to a new contact cannot be sealed.** Sealing needs the recipient's delivery key and that key travels inside an E2E message, so a prior exchange is required. `Sent.sealed` reports which happened rather than leaving the UI free to imply anonymity that was not achieved — a silent fall back to an unsealed send is exactly what §14.5 warns about. ⚠️ **Rotation is blunt, and the copy says so.** There is no sender to block, so the only lever is replacing the delivery key, which cuts off every contact until the next time they are written to. Reachable from Account, asserted by `CrudSurfaceTest`, and live-tested: a submission presenting a retired key is refused by the relay. The relay stores only `SHA-256(key)`. The key itself never passes through the relay from its owner, which is the only reason an unauthenticated sealed submission can be authorised without naming who is submitting. Tested: 108 engine, 67 client, 43 interop, none failing, live suites enabled. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Flamenet Messenger — Android
Nothing here is an app yet. This is the engine, and it is deliberately first.
An Android client needs the protocol implemented a third time. That third
implementation is the one that finds the places where the specification says
less than the two existing engines quietly agreed on — but only if it is
written against the spec and the published vectors rather than against a
reading of our own Swift and JavaScript. So the engine comes first, it is a
plain Kotlin/JVM library with no Android in it at all, and it is held to
engine/test/vectors/protocol-v1.json — the same file the other two engines
are checked against, read from that one location rather than copied here.
./gradlew :engine:test
No Android SDK, no emulator, no device. It runs anywhere a JVM does, which is also what lets it run in CI on Linux.
What the engine covers today
| Area | Spec | State |
|---|---|---|
| Safety numbers | §7 | Done — fingerprints and conversation ordering match the published vectors |
| Key transparency verification | §19 | Done — RFC 6962 leaf/node hashing, unbalanced split, bottom-up audit paths |
| Byte helpers | — | Unsigned comparison, constant-time equality |
What it does not cover
Listed rather than left to be discovered, because a table of green ticks with the hard parts quietly missing is worse than no table:
| Area | Spec | State |
|---|---|---|
| X25519 / Ed25519 | §3 | Not started — needs a provider that works on both JVM and Android |
| X3DH key agreement | §4 | Not started |
| Double Ratchet | §6 | Not started |
| Sealed sender | §12 | Not started |
| ML-KEM-768 hybrid | §11 | Not started |
| ML-DSA-65 identities | §20 | Not started |
| Relay client | §8 | Not started |
| The app itself | — | Not started |
Until those exist, Android is honestly marked "not started" on the website, and a conversation gets the protocol's guarantees only when both ends are iOS.
Why the vectors matter more than the code
Two implementations that agree may both be wrong in the same way, especially when one was written while reading the other. The audit-path ordering in §19 is the worked example: a top-down reading of a bottom-up path produces the correct root for every left-spine index, so it passes any test that only checks index 0. The vector file pins a right-descending index for that reason, and the Kotlin tests assert both that the published path verifies and that the same path reversed does not.
If this engine ever disagrees with the file, the interesting question is which of the three is wrong — not this one by default.