LXMF Protocol Specification

This appendix is an exact, English specification of the LXMF messaging protocol, derived from and proven against the vendored Python reference (vendor/LXMF, v0.9.6, commit 8499729) running on Reticulum (vendor/Reticulum, RNS 1.3.5, commit d5e62d4). It is the contract the libreticulum lxmf crate is built and tested against.

LXMF (Lightweight Extensible Message Format) is the store-and-forward messaging layer of Reticulum. It defines how a message is structured, signed, encrypted, sized, and delivered (opportunistically as a single packet, directly over a link, via a propagation node, or on paper), plus the anti-spam stamp and ticket mechanisms. It moves opaque bytes over Reticulum primitives; it carries no media processing of its own.

How to read this specification

• Normative statements use RFC 2119 keywords (MUST, SHOULD, MAY) and specify behaviour an interoperable implementation has to reproduce. Every normative fact carries either a file:line citation into the reference, a derivation with the arithmetic shown, or a labelled test vector [VEC-...].
• Informative sections describe internal reference behaviour (router scheduling, queues, persistence) that an implementation MAY diverge from without breaking wire or semantic compatibility.
• Test vectors are the genuine byte output of the reference, regenerated by vectors/gen_vectors.py and pinned to the submodule commits. A citation proves “the code says this”; a vector proves “these are the bytes”.

Sections

• Introduction and scope
• Cryptographic primitives
• Identifiers and sizes
• Message binary format
• Fields
• Delivery methods and sizing
• On-air sequences
• Stamps and proof-of-work
• Tickets
• Announce application data
• Propagation
• Router internals (informative)
• Constants reference
• Coverage ledger
• Test vectors
• Symbol inventory (frozen)