quicnprotochat
End-to-end encrypted group messaging over QUIC + TLS 1.3 + MLS (RFC 9420), written in Rust.
Every byte on the wire is protected by a QUIC transport secured with TLS 1.3
(quinn + rustls). 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.
┌─────────────────────────────────────────────┐
│ Application / MLS ciphertext │ <- group key ratchet (RFC 9420)
├─────────────────────────────────────────────┤
│ Cap'n Proto RPC │ <- typed, schema-versioned framing
├─────────────────────────────────────────────┤
│ QUIC + TLS 1.3 (quinn/rustls) │ <- mutual auth + transport secrecy
└─────────────────────────────────────────────┘
| Property | Mechanism |
|---|---|
| Transport confidentiality | TLS 1.3 over QUIC (rustls) |
| Transport authentication | TLS 1.3 server cert (self-signed by default) |
| 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) |
Documentation
Full documentation is available as an mdBook wiki in docs/:
# Install mdBook (once)
cargo install mdbook
# Build and serve locally
mdbook serve docs
# Open http://localhost:3000
Highlights
- Architecture Overview — Two-service model, dual-key design, crate layout
- Protocol Deep Dives — QUIC/TLS 1.3, Cap'n Proto, MLS, Hybrid KEM
- Cryptographic Properties — Forward secrecy, post-compromise security, PQ readiness, threat model
- Design Rationale — Why MLS over Signal/Matrix, ADRs for all key decisions
- Wire Format Reference — Annotated Cap'n Proto schemas
- Getting Started — Build, run, demo walkthrough
- Roadmap — Milestones, production readiness, future research
Quick start
# Prerequisites: Rust 1.77+, capnp CLI
brew install capnp # macOS
# apt-get install capnproto # Debian/Ubuntu
# GUI prerequisites (Linux only) — WebKitGTK + GTK3 for Tauri 2
# sudo apt install -y libwebkit2gtk-4.1-dev libgtk-3-dev libglib2.0-dev libssl-dev libayatana-appindicator3-dev librsvg2-dev patchelf
# Build and test
cargo build --workspace
cargo test --workspace
# Start the server (port 7000 by default)
cargo run -p quicnprotochat-server
# Or via a config file (TOML)
cat > quicnprotochat-server.toml <<'EOF'
listen = "0.0.0.0:7000"
data_dir = "data"
tls_cert = "data/server-cert.der"
tls_key = "data/server-key.der"
auth_token = "devtoken"
store_backend = "file" # or "sql"
db_path = "data/quicnprotochat.db"
db_key = ""
EOF
cargo run -p quicnprotochat-server -- --config quicnprotochat-server.toml
# Run the two-party demo
cargo run -p quicnprotochat-client -- demo-group \
--server 127.0.0.1:7000
# Interactive 1:1 chat (after creating a group and inviting a peer)
# Terminal 1: quicnprotochat chat --peer-key <other_identity_hex>
# Terminal 2: quicnprotochat chat --peer-key <first_identity_hex>
# Type messages and press Enter; incoming messages appear as [peer] <msg>. Ctrl+D to exit.
See the full demo walkthrough for a step-by-step guide.
Milestones
| # | Name | Status | What it adds |
|---|---|---|---|
| M1 | QUIC/TLS transport | Done | QUIC + TLS 1.3 endpoint, length-prefixed framing, Ping/Pong |
| M2 | Authentication Service | Done | Ed25519 identity, KeyPackage generation, AS upload/fetch |
| M3 | Delivery Service + MLS groups | Done | DS relay, GroupMember create/join/add/send/recv |
| M4 | Group CLI subcommands | Done | Persistent CLI (create-group, invite, join, send, recv), OPAQUE login |
| M5 | Multi-party groups | Done | N > 2 members, Commit fan-out, send --all, epoch sync |
| M6 | Persistence | Done | SQLite/SQLCipher, migrations, durable server + client state |
| M7 | Post-quantum | Next | PQ hybrid for MLS/HPKE (X25519 + ML-KEM-768) |
Security notes
This is a proof-of-concept research project. It has not been audited. See the threat model for a detailed analysis of what is and isn't protected.
License
MIT