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