# 文 fumi [![License: Apache-2.0](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](LICENSE) [![AI-DECLARATION: auto](https://img.shields.io/badge/%E4%B7%BC%20AI--DECLARATION-auto-ede9fe?labelColor=ede9fe)](https://ai-declaration.md) A Rust client for [Smol Mail](https://code.randogoth.com/randogoth/smolmail): a minimalist, end-to-end encrypted mail protocol over a Noise-secured TCP connection. `fumi` derives an identity from one 32-byte master secret, seals and opens mail, and talks to a mailbox; it is the counterpart to [bunshin](https://code.randogoth.com/randogoth/bunshin), the server. ## Status Both carriers are implemented: the TCP carrier (SPEC.md 1.1) and the Reticulum carrier of RNS.md (1.2), the latter behind the `rns` cargo feature (`nix build .#rns`). `fumi` interoperates in both directions with the reference stack — `smolmail.py`/`smolmaild.py` over TCP and `smolmail_rns.py`/`smolmaild_rns.py` over Reticulum — and with `bunshin` over both carriers, including the cross-transport case upstream section 15 promises: send over TCP, fetch over the mesh, one mailbox. ## Addressing ``` alice@example.org[:1961] short form, resolved via the server smol://alice@example.org/mfrggzdfzt... self-certifying, 52-char base32 identity smol+rns://alice@8f2c1d0a7b6e5f4c3d2a1b0e9f8c7d6a short form over Reticulum (rns feature) smol+rns://alice@8f2c1d0a7b6e5f4c3d2a1b0e9f8c7d6a/mfrggzdfzt... self-certifying over Reticulum ``` ## Usage One master per store, selected by the global `--key` and `--db` flags; a second identity is a second pair of files. ``` fumi [--key identity.key] [--db fumi.db] [--timeout 30] # identity fumi keygen [--force] create a master secret fumi whoami address, public key, fingerprint, rotation index fumi restore
recover local state from the master alone fumi rotate advance the rotation index, sign and push the certificate # servers and contacts fumi trust [--force] pin a server's Noise static key fumi register
[--invite TOKEN] bind this identity to a username fumi resolve
look up a contact's key, walk the chain, pin it fumi import add a contact from a self-certifying address fumi contacts known keys and how each was learned # accept tokens fumi accept
issue a token, admit to the main tier, sync the set fumi block
withdraw it, sync the set # mail fumi send
[--subject S] [--body TEXT | --file F | -] [--header K:V] [--reply-to ID] [--anonymous] [--no-pad] fumi fetch [--keep] [--reset] retrieve, verify, store, acknowledge fumi delete ... remove from the server explicitly fumi list [--sent] [--requests] fumi read [--sent] # RNS carrier (built with --features rns / nix build .#rns); addresses select # it by scheme, so these flags apply only to smol+rns:// dials: fumi --rns-udp --rns-udp-forward [--rns-storage DIR] ``` On the mesh the destination hash is the pin (RNS.md 13.4): there is no `trust`, no static key, and a client creates no Reticulum identity (13.8). The `--rns-udp-forward` target is effectively required for a client, which speaks first; it should point at an `rnsd` or at the server's UDP interface. Requests carry an explicit 30-second timeout (13.5), links are torn down when a session ends (13.10), and a resend is safe because ids are derived. Mail is stored sealed and opened on demand; there is no plaintext at rest. A first contact is learned by trust on first use and marked unverified when the server's key was not pinned; a key change is accepted only when a signed rotation chain leads from the key held to the one offered, and is surfaced rather than applied silently. ## Build ``` nix build # or: nix develop -c cargo build nix develop -c cargo test --workspace ``` The crate is a workspace: `core/` is the `fumi-core` library — everything but the command line — and `cli/` is the `fumi` binary. GUI hosts depend on `fumi-core` alone; it pulls no argument parsing, no logging globals, and no keyfile conventions. `bundled-sqlite` (default) vendors libsqlite3; embedders that link their own SQLite, as Android's NDK does, build with `default-features = false`. `bunshin` and the reference clients make a complete test rig: register against a local server, exchange mail in both directions, then rotate and fetch the mail that the superseded key still receives. ## Embedding `fumi-core` is the protocol core of a GUI client, not just this CLI's engine. The contract an embedder can rely on: - **Secrets stay bytes in the API, files stay in the CLI.** `Account::new(master, index)` takes the master as bytes and `Store::open(path)` takes only mail and state; `identity.key` next to `fumi.db` is a CLI convention. A GUI keeps the master wherever its platform wants it (Android Keystore, OS keychain) and hands it over per operation. - **One shareable store handle.** `Store` is `Send + Sync`: every operation locks an inner mutex, and the database runs in WAL mode, so a host holds one `Store` behind an executor and reads it while a fetch writes. Each envelope is committed as it is verified — a concurrent reader listing the inbox sees fetch progress without any callback. - **Decisions, not prose.** `error::Error` is an enum: `NotPinned`, `PinMismatch`, `KeyChanged { address, known, offered }`, `NotRegistered`, `AuthFailed`, `RateLimited`, `QuotaExceeded`, `SchemaVersion`, ... — the distinctions a UI routes on. `Display` still produces the message the CLI prints. - **Long operations can stop.** `fetch_with` takes a `FetchOptions` with a cancellation token checked between pages; the cursor is saved per page, so a cancelled fetch resumes rather than repeats. - **Composable flows.** `restore` remains the one-call convenience, but its pieces are public: `connect` + `resolve`, `account::find_rotation_index`, then the `Store` setters — a wizard can hold the master and the address before it has connectivity, and show each step. Trust outcomes arrive as values: `TrustChange` from `trust_key` and `send`, `Session::unpinned_static` for the sec 4 warning. - **A versioned store.** The schema carries a `user_version`; a store written by a newer build is refused (`Error::SchemaVersion`) rather than misread, and within a version the schema is stable. The host, not the library, decides when to upgrade the binary. - **Binding from other languages.** The API is `Send`-friendly and free of CLI globals, so plain Rust bindings (flutter_rust_bridge, uniffi) work against it. `core/vectors.json` holds the reference vectors the unit tests pin — derivations, seals, a full envelope — so a port or FFI binding can verify itself end to end without the reference stack. The intended call graph: `Store::open` once, `Account::new(master, rotations)` per session, then `client::*` operations taking `&Store` and `&Account`. The store outlives accounts; nothing in the library caches between calls. ## Modules | File | Contents | |---|---| | `core/src/crypto.rs` | base32, HKDF, HMAC, SHA-256, the Ed25519→X25519 map with SPEC.md §2's checks | | `core/src/address.rs` | parsing for all four address forms, username validation, fingerprints | | `core/src/account.rs` | master, `seed_n` derivation, accept-key and tokens, rotation certificates, `find_rotation_index` | | `core/src/message.rs` | envelope seal/open (§5.1–§5.3), message id (§5.4), frontmatter (§5.5) | | `core/src/transport.rs` | `Transport` trait, bind values, operation and status constants | | `core/src/tcp.rs` | Noise_NX initiator, `len u32 \|\| op u8 \|\| body` framing, static-key pinning | | `core/src/rns/` | the Reticulum carrier behind the `rns` feature: FFI over `core/shim/`, path discovery, one link per session | | `core/src/client.rs` | the six operations, AUTH, chain walking, token sync, fetch pipeline with cancellation | | `core/src/store.rs` | SQLite: state, contacts, accepted, tokens, seen ids, inbox, sent; `Send + Sync`, WAL, versioned schema | | `core/src/error.rs` | the `Error` enum embedders match on, the status-code mapping | | `core/vectors.json` | the committed reference vectors, the tests' source of truth | | `cli/src/main.rs` | the command line: keyfile and `--db` conventions, hints, output | Unit tests pin every derivation against `vectors.json`, whose values were generated from `smolmail.py`, including a full envelope reproduced byte for byte. ## References - [SPEC.md](https://code.randogoth.com/randogoth/smolmail/src/branch/main/SPEC.md) — protocol 1.1 - [RNS.md](https://code.randogoth.com/randogoth/smolmail/src/branch/main/RNS.md) — the 1.2 Reticulum addendum - [bunshin](https://code.randogoth.com/randogoth/bunshin) — the server