# QPQ — quicproquo > End-to-end encrypted messaging over **QUIC + TLS 1.3 + MLS** (RFC 9420), written in Rust. The server never sees plaintext. Every byte on the wire is protected by a QUIC transport secured with TLS 1.3 (`quinn` + `rustls`). The inner **MLS** layer provides forward secrecy, post-compromise security, and ratcheted group key agreement across any number of participants. Messages are framed with **Cap'n Proto** for zero-copy, schema-versioned serialisation. ``` ┌─────────────────────────────────────────────┐ │ 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 or CA) | | Group key agreement | MLS `MLS_128_DHKEMX25519_AES128GCM_SHA256_Ed25519` | | Post-compromise security | MLS epoch ratchet | | Forward secrecy | Per-epoch key schedule | | Identity | Ed25519 (MLS credential + leaf node signature) | | Password auth | OPAQUE (password never sent to server) | | Post-quantum readiness | X25519 + ML-KEM-768 hybrid KEM envelope | | Local storage encryption | SQLCipher + Argon2id + ChaCha20-Poly1305 | | Message framing | Cap'n Proto (unpacked wire format) | --- ## Features ### Working - **Interactive REPL** — multi-conversation chat with auto-register, auto-login, slash commands, background polling, and message history - **1:1 DMs** — dedicated channels with server-enforced membership authorization - **Multi-party groups** — N-member MLS groups with Commit fan-out and epoch sync - **OPAQUE authentication** — password-authenticated key exchange (password never leaves the client) - **Encrypted local storage** — SQLCipher database + encrypted session tokens (Argon2id + ChaCha20-Poly1305) - **Persistent state** — server and client survive restarts; SQLite/SQLCipher or file-backed storage - **Self-DM notepad** — send messages to yourself (local-only, no server round-trip) - **Certificate pinning** — pass the server cert as `--ca-cert` to trust only that server - **18 CLI subcommands** — `register-user`, `login`, `create-group`, `invite`, `join`, `send`, `recv`, `chat`, `repl`, and more ### REPL slash commands | Command | Description | |---|---| | `/dm ` | Start a 1:1 DM with a peer | | `/create-group ` | Create a new group | | `/invite ` | Add a member to the current group | | `/join` | Join a pending group invitation | | `/switch @user` or `/switch #group` | Switch active conversation | | `/list` or `/ls` | List all conversations | | `/members` | Show group members | | `/history [count]` | Show message history (default 20) | | `/whoami` | Show identity and group status | | `/help` | Command reference | | `/quit` | Exit | ### Experimental / proof-of-concept - **Tauri 2 GUI** (`quicproquo-gui`) — foundational desktop app shell; not feature-complete - **Mobile FFI** (`quicproquo-mobile`) — C API for QUIC connection migration (wifi to cellular) - **P2P transport** (`quicproquo-p2p`) — iroh-based direct peer-to-peer messaging with NAT traversal (excluded from default build) --- ## Quick start ```bash # 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 --bin qpq-server # Run the two-party demo cargo run --bin qpq -- demo-group --server 127.0.0.1:7000 # Interactive REPL (auto-registers and logs in) cargo run --bin qpq -- repl --username alice --password mypass ``` ### REPL quickstart (two terminals) ```bash # Terminal 1 qpq repl --username alice --password secretA # Terminal 2 qpq repl --username bob --password secretB # In Alice's REPL: /dm bob Hello from Alice! # Bob sees: [alice] Hello from Alice! ``` ### Server configuration (TOML) ```bash cat > qpq-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 = "sql" # or "file" db_path = "data/qpq.db" db_key = "" # set for SQLCipher encryption EOF cargo run --bin qpq-server -- --config qpq-server.toml ``` > **Production:** set `QPQ_PRODUCTION=1`, use a strong `QPQ_AUTH_TOKEN` (not `devtoken`), and set `QPQ_DB_KEY` when using `store_backend = "sql"`. See the [full demo walkthrough](docs/src/getting-started/demo-walkthrough.md) for a step-by-step guide. --- ## Crate layout | Crate | Purpose | |---|---| | `quicproquo-core` | MLS group operations, hybrid KEM, OPAQUE auth, crypto primitives | | `quicproquo-proto` | Cap'n Proto schemas and generated RPC code | | `quicproquo-server` | QUIC server, NodeService RPC, storage backends | | `quicproquo-client` | CLI + REPL, session management, conversation store | | `quicproquo-gui` | Tauri 2 desktop app (experimental) | | `quicproquo-mobile` | C FFI for mobile connection migration (experimental) | | `quicproquo-p2p` | iroh-based P2P transport (experimental, excluded from workspace) | --- ## 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, OPAQUE login, 18 subcommands | | M5 | Multi-party groups | **Done** | N > 2 members, Commit fan-out, `send --all`, epoch sync | | M6 | Persistence + REPL | **Done** | SQLite/SQLCipher, interactive REPL, DM channels, encrypted local storage | | M7 | Post-quantum MLS | **Next** | Hybrid X25519 + ML-KEM-768 integrated into MLS ciphersuite | M7 note: the hybrid KEM envelope is already implemented and tested (10 tests passing). What remains is integrating it into the OpenMLS CryptoProvider so all MLS key material gets post-quantum confidentiality. --- ## Roadmap ### Next up - **Post-quantum MLS integration** (M7) — hybrid KEM into the MLS key schedule - **Full MLS lifecycle** — member removal, credential updates, proposal handling - **CI pipeline** — GitHub Actions (test, clippy, fmt, audit) - **Accounts & devices model** — per-account rate limits, multi-device support - **Client offline queue** — idempotent message IDs, gap detection, retry ### Planned - Server-to-server federation (mTLS relay, in progress) - CA-signed TLS / Let's Encrypt support - HTTP health endpoint for load balancers - Connection draining and graceful shutdown - Wire versioning and N-1 compatibility ### Research - Sealed sender (metadata resistance) — foundation exists - Traffic analysis resistance (padding + shaping) - P2P / NAT traversal via iroh — crate started - WebTransport for browser clients - Tor / I2P routing - Private information retrieval for message fetch --- ## Building without the GUI ```bash cargo build --bin qpq-server --bin qpq ``` Core and proto crates are built as dependencies automatically. --- ## Documentation Full documentation is available as an **mdBook** in [`docs/`](docs/): ```bash cargo install mdbook # once mdbook serve docs # http://localhost:3000 ``` - **[Architecture Overview](docs/src/architecture/overview.md)** — two-service model, dual-key design, crate layout - **[Protocol Deep Dives](docs/src/protocol-layers/overview.md)** — QUIC/TLS 1.3, Cap'n Proto, MLS, Hybrid KEM - **[Cryptographic Properties](docs/src/cryptography/overview.md)** — forward secrecy, post-compromise security, PQ readiness, threat model - **[Design Rationale](docs/src/design-rationale/overview.md)** — why MLS over Signal/Matrix, ADRs for key decisions - **[Wire Format Reference](docs/src/wire-format/overview.md)** — annotated Cap'n Proto schemas - **[Getting Started](docs/src/getting-started/prerequisites.md)** — build, run, demo walkthrough - **[Roadmap](docs/src/roadmap/milestones.md)** — milestones, production readiness, future research - **[Future Improvements](docs/FUTURE-IMPROVEMENTS.md)** — prioritised list of security, ops, and feature improvements --- ## Security This is a **research project** and has not undergone a formal third-party audit. See the [threat model](docs/src/cryptography/threat-model.md) and [security audit](docs/SECURITY-AUDIT.md) for details. - The server only routes opaque ciphertexts by recipient key — it never sees plaintext. - OPAQUE ensures passwords never leave the client. - Local databases are encrypted with SQLCipher when a password is provided. - Session tokens are encrypted at rest (Argon2id key derivation + ChaCha20-Poly1305). - **Certificate pinning:** pass the server cert as `--ca-cert` so the client trusts only that server. - **Dependency checks:** `cargo install cargo-audit && cargo audit` --- ## License MIT