Paul HittandClaude Opus 5
fc93df24e6
The seventeen Kotlin tests that landed with X3DH and the ratchet prove the engine agrees with itself. That is not the property anyone needs. Two engines written by the same person agree about the same misreadings of the spec, and every one of those shows up months later as "the message will not decrypt" on someone else's phone. So this wires the Kotlin engine up against the web engine, which is normative, in both directions. 23 assertions, all passing: v1 X3DH both ways, identical associated data, alternating ratchet turns past the handshake, out-of-order and permanently lost messages, a drained one-time prekey pool, tamper rejection, safety numbers, and the canonical transparency-log leaf. Three things worth recording. Ed25519 was missing, and the engine could derive an account address but never sign a claim for one. The JCA offers no route from a private EdDSA key to its public half, so the RFC 8032 keygen is done here -- and verified against the RFC 8032 test vectors, not against a round-trip through our own code. A round-trip proves only that the file agrees with itself, and every wrong clamp, endianness and sign convention agrees with itself perfectly. The scalar multiplication uses BigInteger and is therefore not constant-time; it runs once at sign-in, in the user's own process, and signing deliberately stays with the platform provider. The harness reports a build failure as a failure, never a skip. The Swift harness beside it once printed "skipped" -- which reads as green -- while silently building a different checkout. Only a missing JDK skips here, and the resolved path is printed either way. Each section is wrapped so a divergence is a named failure rather than a crash. That was not theoretical: breaking the Kotlin message-key derivation on purpose crashed the process with a stack trace and skipped every later section. It now reports four failing sections and finishes the run. The negative control is how this was checked at all -- a suite that passes on its first run and has never been seen to fail is not evidence of anything. 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.