offline-protocol-leaf
A constrained device that speaks the Offline Protocol as a real peer: a door lock, a sensor, a mains-powered relay. It parses frames, validates addressing, runs RFC 9420 MLS through mls-rs, and holds an end-to-end encrypted conversation with a phone under the same guarantees a phone gets. Same frames, same envelope, same trust gates, no second sealing path.
Provides:
LeafDevice, a frame-level state machine: hand it an inbound message, get back the frames to send and what happened- The never-committing member profile, where the phone creates the group and issues every commit and the device joins, opens, answers and persists
LeafStore, one blob-storage seam a device implements over its secure key storage, with persist-before-emit enforced rather than documented- Key package minting with the backdated
not_beforeand supplied timestamp a device needs to pair at all
Four obligations this crate cannot discharge for you: a time source at pairing (every entry point takes now_unix_secs, because a device that lets an MLS library read a clock it does not have stamps 1970 and is refused as expired), real entropy (this crate registers no getrandom backend on purpose; wire the symbol to the part's hardware source), durable storage (LeafStore must be atomic per entry, because a ratchet state rolled back by a power cut reuses an AEAD nonce), and authorization (a session proves who a peer is and never that the owner meant them, since any address in radio range can complete a pairing, so firmware decides when the radio accepts one and what a given peer may actuate).
Like offline-protocol-core and offline-protocol-sealed, this crate compiles for bare-metal targets with --no-default-features (add --features bare-metal-rng). CI builds and lints it for the first four of these:
| Chip family | Rust target | This crate compiles | Inside an esp-hal 1.2.2 firmware |
|---|---|---|---|
| Cortex-M33 (for example Silicon Labs xG24) | thumbv8m.main-none-eabihf |
Yes | Not applicable |
| ESP32-C6, ESP32-H2 | riscv32imac-unknown-none-elf |
Yes | Type-checks (checked by hand) |
| ESP32-C3, ESP32-C2 | riscv32imc-unknown-none-elf |
Yes | Refused: mls-rs and esp-hal select conflicting portable-atomic backends (checked by hand) |
| Cortex-M0 and M0+ (for example RP2040) | thumbv6m-none-eabi |
Yes | Not applicable |
| ESP32, ESP32-S3 | Xtensa, outside rustup | Not tried | Not tried |
| ESP32-S2 | Xtensa, outside rustup | Not tried | Not tried; expected to hit the same refusal, since it has no compare-and-swap and esp-hal selects the same backend for it |
The ESP32-C3, ESP32-C2 and Cortex-M0 targets have no atomic compare-and-swap, so on them the firmware must link a critical-section implementation. Build the store handle with shared_store, which works on every target.
The last column was checked once by hand, with a scratch firmware crate that depends on esp-hal 1.2.2 and on this crate, running cargo check. CI does not repeat it. The third column is what CI gates.
Compiling is all this table claims. Nothing here has been linked into a firmware image or run on a board, and a device still owes a radio, a flash driver behind LeafStore, a hardware entropy source behind getrandom, and a time source at pairing.
The crate also builds for a WebAssembly host, on the WASI target wasm32-wasip1, and CI gates both halves there: the no_std build with no bare-metal-rng, because on WASI getrandom reads the runtime's random_get and there is no symbol for the host to register, and the std build through examples/wasi_host_shim.rs, a shim that takes the time and the frames from the runtime over its standard streams. wasm32-unknown-unknown is not claimed: on that target the pinned mls-rs enables getrandom's js feature, which is selected ahead of a host-registered backend, so a green build there says nothing about a non-browser host. Entropy on WASI is the runtime's, and every key is exactly as strong as the runtime's source.
This crate is for firmware. Applications on a phone want the main offline-protocol crate instead, or the React Native or Python bindings.
License
Copyright © 2025-2026 Offline Protocol, Inc.
Dual-licensed: AGPL-3.0-only for open-source use, or a commercial license for proprietary use.