Paul HittandClaude Opus 5
4f15beb160
The retained-session fix was necessary and did not work, and a live two-peer
reproduction is what showed it: both second-exchange messages still vanished
with delivered:1, failed:0.
Cause. `DoubleRatchet` is a final class on iOS and `E2ESession` is a class on
Android, so the failed decrypt that PROVES the peer is on another chain mutates
the instance it was handed — skipped keys consumed, chain stepped. Both fixes
then archived that same instance. Storing a part-advanced chain is
indistinguishable from storing nothing: it cannot open what the peer sends. The
vault copy was never handed to a decrypt, so re-read it before retiring it.
Second cause, Android only. Which slot the winner belongs in is not the same
question as which chain opened it. When the retired chain opens an envelope it
has to be written back to the RETIRED slot; promoting it swaps the two and
discards the chain we are sending on. Each branch now writes back deliberately
instead of sharing one `if (session !== existing)`.
Verified against relay1, two peer accounts, no simulators:
before p1/p2 poll -> {"messages":[]} / {"messages":[]}
after p1/p2 poll -> second-from-Q2 / second-from-Q1
The repro is in PARITY.md and takes about two minutes.
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.