Paul HittandClaude Opus 5
430f167fc0
64/64 handshakes agree with lyrebird on KEY_SEED, AUTH and KDF output, from both the client and the server side. 23 tests. SipHash is the one primitive hand-written here despite BouncyCastle shipping one, and that is worth justifying because everything else in this module is BouncyCastle's. BC's SipHash is a Mac: doFinal RESETS. obfs4's DRBG writes eight bytes, finalises, writes eight more and finalises again -- without ever resetting. Emulating that with a resetting MAC means re-hashing the whole history per block, O(n^2) in the frames on a connection. So the state machine is written out, and `sum` finalises a COPY. The DRBG is checked ten blocks deep, not one. obfs4's comment says each block is a fresh H(K, previous); the code never resets, so blocks are cumulative. The two readings agree on block one and diverge afterwards -- an implementation built from the comment decodes the first frame of a connection perfectly and then fails. ntor carries the same trap the Swift port hit: the transcript is B | B | X | Y | PROTOID | ID, with B twice, while the comment directly above that code claims ID | B | Y | X | PROTOID. Both orderings produce a well-formed 32-byte KEY_SEED. Only one interoperates. HMAC via javax.crypto, HKDF via BouncyCastle's HKDFBytesGenerator, X25519 via the ladder from part 2. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Flamenet Messenger — Android
The Android app, and the two libraries under it.
engine/ the protocol: X3DH, Double Ratchet, sealed sender, safety numbers,
key transparency. Plain Kotlin/JVM — no Android in it at all.
client/ the relay transport: HTTP, auth, the §8 routes.
app/ the Compose app.
interop/ the cross-engine driver; not shipped.
engine and client are deliberately plain JVM libraries. The protocol has
nothing to do with Android, and keeping it off the platform means their tests
run anywhere a JVM does — no SDK, no emulator, no device, which is also what
lets them gate in CI on Linux:
./gradlew :engine:test :client:test
The app's own unit tests need the Android SDK but still no emulator (Robolectric):
./gradlew :app:testDebugUnitTest
Where it stands
PARITY.md is the definition of done for this app — read that, not this. Every row there names the iOS file it came from so it can be re-checked rather than trusted. Headlines as of 2026-08-28: messaging, groups, attachments, voice notes, stories, calls, sealed sender, key transparency and the encrypted vault are built and tested; a cross-platform round trip against iOS was verified on 2026-08-26.
⚠️ This file said "Nothing here is an app yet" until 2026-08-28, above a tree containing the finished app — the README described the repository as it was when the engine landed and nothing updated it as the app grew around it. If a claim here ever disagrees with PARITY.md or with the tree, believe those, and fix this.
Why the engine came first, and is held to the vectors
An Android client needs the protocol implemented a third time, and the 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 is held to
test/vectors/protocol-v1.json in
flamenet-e2e — the same file the
other two engines are checked against, read from that repository rather than
copied here, because a copied vector file drifts and a drifting vector file
stops being a check. PublishedVectorsTest looks for it beside this checkout
and fails loudly if it cannot find it; FLAMENET_VECTORS overrides the search.
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.
Contributing and security
- CONTRIBUTING.md — building (JDK 21,
JAVA_HOMEis not optional on a Mac), the test gate, and the platform traps that cost an hour each. - PARITY.md — what iOS does, what this does, and what is left. It is the definition of done for this app.
- SECURITY.md — threat model and where to send a vulnerability report. Not an issue tracker matter: security@flamenetmessenger.com.