# quicnprotochat > End-to-end encrypted group messaging over **Noise_XX + MLS** (RFC 9420), written in Rust. Every byte on the wire is double-protected: the outer **Noise_XX** channel authenticates both sides and provides forward secrecy for the transport, while the inner **MLS** layer provides post-compromise security and ratcheted group key agreement across any number of participants. Messages are framed with **Cap'n Proto**, keeping serialisation zero-copy and schema-versioned. --- ## Protocol stack ``` ┌─────────────────────────────────────────────┐ │ Application / MLS ciphertext │ <- group key ratchet (RFC 9420) ├─────────────────────────────────────────────┤ │ Cap'n Proto RPC │ <- typed, schema-versioned framing ├─────────────────────────────────────────────┤ │ Noise_XX (X25519 · ChaChaPoly · SHA-256) │ <- mutual auth + transport secrecy ├─────────────────────────────────────────────┤ │ TCP │ └─────────────────────────────────────────────┘ ``` | Property | Mechanism | |---|---| | Transport confidentiality | Noise_XX (ChaCha20-Poly1305) | | Transport authentication | Noise_XX static X25519 keys | | Group key agreement | MLS `MLS_128_DHKEMX25519_AES128GCM_SHA256_Ed25519` | | Post-compromise security | MLS epoch ratchet | | Identity | Ed25519 (MLS credential + leaf node signature) | | Message framing | Cap'n Proto (unpacked wire format) | --- ## Repository layout ``` quicnprotochat/ ├── crates/ │ ├── quicnprotochat-core/ # Crypto primitives, Noise transport, MLS group state machine │ │ ├── src/codec.rs # LengthPrefixedCodec — Tokio Encoder + Decoder │ │ ├── src/keypair.rs # NoiseKeypair — X25519 static key, zeroize-on-drop │ │ ├── src/identity.rs # IdentityKeypair — Ed25519 identity + MLS Signer │ │ ├── src/keypackage.rs# generate_key_package — standalone KeyPackage helper │ │ ├── src/noise.rs # handshake_initiator / handshake_responder / NoiseTransport │ │ └── src/group.rs # GroupMember — full MLS group lifecycle │ │ │ ├── quicnprotochat-proto/ # Cap'n Proto schemas + generated types + serde helpers │ │ └── schemas/ → # (symlinked to workspace root schemas/) │ │ │ ├── quicnprotochat-server/ # Authentication Service (AS) + Delivery Service (DS) binary │ └── quicnprotochat-client/ # CLI client (ping, register, fetch-key, …) │ └── schemas/ ├── envelope.capnp # Top-level wire envelope (MsgType discriminant + payload) ├── auth.capnp # AuthenticationService RPC (KeyPackage upload / fetch) └── delivery.capnp # DeliveryService RPC (enqueue / fetch MLS messages) ``` --- ## Services ### Authentication Service (AS) — port 7000 Stores single-use MLS KeyPackages so peers can add each other to groups. ``` uploadKeyPackage(identityKey: Data, package: Data) -> (fingerprint: Data) fetchKeyPackage(identityKey: Data) -> (package: Data) ``` Packages are indexed by the raw Ed25519 public key (32 bytes) and consumed exactly once on fetch, matching the MLS single-use KeyPackage requirement. ### Delivery Service (DS) — port 7001 A simple store-and-forward relay for MLS messages. The DS never inspects payloads — it routes opaque blobs by recipient public key. ``` enqueue(recipientKey: Data, payload: Data) -> () fetch(recipientKey: Data) -> (payloads: List(Data)) ``` `fetch` atomically drains the entire queue in FIFO order. --- ## MLS group lifecycle ``` GroupMember::new(identity) │ ├─ generate_key_package() → upload bytes to AS │ ├─ create_group(group_id) → epoch 0, sole member │ └─ add_member(kp_bytes)→ (commit_bytes, welcome_bytes) │ ↑ │ │ │ fetched from AS discard send to joiner via DS │ └─ join_group(welcome_bytes) → joined; ready to encrypt ├─ send_message(plain) → TLS-encoded PrivateMessage → DS └─ receive_message(ct) → Some(plaintext) | None (Commit) ``` The `OpenMlsRustCrypto` backend is **persistent across calls** on the same `GroupMember` instance — it holds the HPKE init private key in its in-memory key store between `generate_key_package` and `join_group`. --- ## Building **Prerequisites:** - Rust (stable, 1.77+) - `capnp` CLI — the Cap'n Proto schema compiler ```bash # Debian / Ubuntu apt-get install capnproto # macOS brew install capnp ``` **Build everything:** ```bash cargo build --workspace ``` **Run tests:** ```bash cargo test --workspace ``` --- ## Running **Start the server** (AS on :7000, DS on :7001): ```bash cargo run -p quicnprotochat-server # or with custom ports: cargo run -p quicnprotochat-server -- --listen 0.0.0.0:7000 --ds-listen 0.0.0.0:7001 ``` **Client commands:** ```bash # Check connectivity cargo run -p quicnprotochat-client -- ping # Generate a fresh identity + KeyPackage, upload to AS # Prints your identity_key (hex) — share this with peers cargo run -p quicnprotochat-client -- register # Fetch a peer's KeyPackage (they must have registered first) cargo run -p quicnprotochat-client -- fetch-key <64-hex-char identity key> # Run an end-to-end Alice↔Bob demo against live AS + DS cargo run -p quicnprotochat-client -- demo-group \ --server 127.0.0.1:7000 \ --ds-server 127.0.0.1:7001 # Persistent group CLI (stateful) cargo run -p quicnprotochat-client -- register-state --state state.bin --server 127.0.0.1:7000 cargo run -p quicnprotochat-client -- create-group --state state.bin --group-id my-group cargo run -p quicnprotochat-client -- invite --state state.bin --peer-key --server 127.0.0.1:7000 --ds-server 127.0.0.1:7001 cargo run -p quicnprotochat-client -- join --state state.bin --ds-server 127.0.0.1:7001 cargo run -p quicnprotochat-client -- send --state state.bin --peer-key --msg "hello" --ds-server 127.0.0.1:7001 cargo run -p quicnprotochat-client -- recv --state state.bin --ds-server 127.0.0.1:7001 ``` Server address defaults to `127.0.0.1:7000`; override with `--server` or `QUICNPROTOCHAT_SERVER`. Delivery Service defaults to `127.0.0.1:7001`; override with `--ds-server` or `QUICNPROTOCHAT_DS_SERVER`. State file notes: the persisted state stores your identity and MLS group state after you have joined. If you generate a KeyPackage (`register-state`) and then restart before consuming the Welcome, the join may fail because the HPKE init key is not retained; run join in the same session you register. --- ## Milestones | # | Name | Status | What it adds | |---|------|--------|--------------| | M1 | Noise transport | ✅ | Noise_XX handshake, length-prefixed framing, Ping/Pong | | M2 | Authentication Service | ✅ | Ed25519 identity, KeyPackage generation, AS upload/fetch | | M3 | Delivery Service + MLS groups | ✅ | DS relay, `GroupMember` create/join/add/send/recv | | M4 | Group CLI subcommands | 🔜 | Persistent CLI (`create-group`, `invite`, `join`, `send`, `recv`); demo-group already available | | M5 | Multi-party groups | 🔜 | N > 2 members, Commit fan-out, Proposal handling | | M6 | Persistence | 🔜 | SQLite key store, durable group state | | M7 | Post-quantum | 🔜 | ML-KEM-768 hybrid in Noise layer | --- ## Security notes - This is a **proof-of-concept**. It has not been audited. - The server Noise keypair is **ephemeral** — regenerated on every restart. Clients perform no server key pinning in the current milestone. - MLS credentials use `CredentialType::Basic` (public key only). A real deployment would bind credentials to a certificate authority. - The Delivery Service does no authentication of the `recipientKey` field — anyone can enqueue for any recipient. Access control is a future milestone. --- ## License MIT