dc0a1438e6
Closes Tier 1 #4. Without this, a clean-room Link implementation that either always emits the signalling slot or always omits it will fail handshakes against the opposite-config peer because the LRPROOF signed_data either includes or excludes the 3 bytes — and the signature verifies against exactly one of those forms. §6.6 covers six sub-sections: §6.6.1 Wire layout. 24-bit big-endian packed value: top 3 bits of byte 0 = mode, low 21 bits = mtu. Citations to encoder at RNS/Link.py:147-151 and decoders at :154+, :171+. §6.6.2 Mode field. 3 bits, values 0..7. Currently only MODE_AES256_CBC = 0x01 is in ENABLED_MODES; six others are reserved (AES-128, AES-256-GCM, OTP, four PQ slots). Sender-side signalling_bytes() raises on disabled modes; receiver-side mode_from_lr_packet returns the raw integer without validation. handshake() at line 353 enforces. §6.6.3 MTU field. 21 bits, max 2,097,151. Forward-looking width; real interfaces are way smaller. Initiator emits its next-hop HW_MTU; responder clamps to min(its-view, requested) by rewriting the LINKREQUEST data buffer in place at RNS/Transport.py:2042-2051 BEFORE Destination.receive runs, so the eventual LRPROOF carries the clamped value. The clamp also leaves link_id invariant because §6.3's hashable_part strips trailing signalling. §6.6.4 Presence detection — purely by body length. Lengths 64 vs 67 for LINKREQUEST, 96 vs 99 for LRPROOF. No flag bit. §6.6.5 Signed_data inclusion rule (the interop break) — the LRPROOF signs over the signalling bytes when present. A peer that omits them when present (or includes them when absent) gets a signed_data mismatch and the link never establishes. §6.6.6 link_mtu_discovery = No config option. Disables emit on the initiator side; receivers don't need a parallel switch (length-dispatch handles it). §6.1 and §6.2 inline references updated to point at §6.6 for the bit layout instead of the previous "[signalling(3)]" placeholder. The existing §6.6 "Source" entry renumbered to §6.7. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com> |
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Reticulum Specifications
Byte-level interoperability specifications for the Reticulum Network Stack and LXMF — the parts that aren't in the upstream manuals but are needed to build a working client from scratch.
Upstream Reticulum has excellent operator-facing documentation (config, deployment, design philosophy). What's missing — and what every alternative implementation has had to reverse-engineer from the Python source — is an authoritative wire-level spec: header bit layouts, msgpack field types, signature input formats, the exact behavior of Transport.outbound, and the long list of "would never guess from reading the manual" gotchas that cost hours of debugging each.
This repo collects those findings in one place. The hope is that future client authors (Kotlin, Swift, Rust, Go, embedded C — pick your stack) can read this instead of re-deriving everything from RNS/Transport.py.
Status
Early days, contributions welcome. Current content was bootstrapped from the working notes of two reverse-engineering efforts:
- The web-based Reticulum client at
reticulum-lora-webclient - The native Android client at
reticulum-mobile-app
Each finding is grounded in upstream source citations (file + line) so it can be re-verified as RNS evolves.
What's here
SPEC.md— the single combined spec document, organized by protocol layerflows/— chronological end-to-end narratives (e.g. "send a message"), cross-referencing SPEC.md sectionstools/— self-contained Python verifier scripts that test SPEC.md claims against upstream RNS / LXMFtest-vectors/— known-good byte sequences each implementation should be able to round-trip (intent: grow into a compliance suite)
As content grows, SPEC.md will be split into per-layer files (packet header, identity, announce, token-crypto, LXMF, link, resource, transport).
Scope
In scope:
- Wire formats: byte layouts, field encodings, framing
- Signing inputs and what's hashed where
- Cross-cutting behaviors required for interop (path requests, ratchet rotation, retransmit semantics)
- "Gotchas" — things upstream code does that aren't obvious from the manual or RFC-style sketches
- Test vectors that any implementation must be able to round-trip
Out of scope:
- Operator/user documentation — see the official manual
- API design choices for any specific implementation
- Networking layer config (interfaces, transport modes) — already well documented
Source citations
Where a finding cites upstream Python code, the path is relative to a standard pip install rns lxmf installation, e.g. RNS/Transport.py, LXMF/LXMF.py. Where the bundled umsgpack is referenced, the path is RNS/vendor/umsgpack.py.
When upstream code changes such that a citation no longer matches, file an issue or PR — the goal is to track the de-facto wire spec as it actually behaves, not as it was at any single snapshot.
Contributing
If you've debugged a Reticulum interop problem and the answer wasn't in the upstream docs, please add it. Format:
### N.M Short description of the finding
**Symptom:** what you observed that prompted the investigation.
**What's happening:** the actual mechanism, ideally with upstream source citation (file + line).
**Implication / fix:** what an implementation must do to interop.
**Source:** upstream file paths and approximate line numbers.
Add a worked test vector to test-vectors/ if the finding is byte-level.
License
CC BY 4.0 — use freely, attribution appreciated.