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)

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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, Noise_XX, 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

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Quick start

# Prerequisites: Rust 1.77+, capnp CLI
brew install capnp          # macOS
# apt-get install capnproto # Debian/Ubuntu

# 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 Alice/Bob demo
cargo run -p quicnprotochat-client -- demo-group \
  --server 127.0.0.1:7000 --ds-server 127.0.0.1:7000

See the full demo walkthrough for a step-by-step guide.

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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	Next	Persistent CLI (create-group, invite, join, send, recv)
M5	Multi-party groups	Planned	N > 2 members, Commit fan-out, Proposal handling
M6	Persistence	Planned	SQLite key store, durable group state
M7	Post-quantum	Planned	PQ hybrid for MLS/HPKE (X25519 + ML-KEM-768)

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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.

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License

MIT