VeilChat — Serverless P2P Messenger

VeilChat is my answer to a question I kept hearing: who knows that we are talking? Every mainstream messenger still needs infrastructure that can log who talked to whom and when. VeilChat removes that layer entirely — two peers open a direct TCP connection, run a mutually-authenticated key exchange, and talk over an encrypted channel that never touches a third party.

The cryptography

I implemented a Noise-inspired handshake from standard primitives — no homemade math:

• Long-term identity — an X25519 key at ~/.veilchat/identity.key, whose SHA-256 fingerprint humans compare out-of-band.
• Forward secrecy — every connection mixes three DH results (ee, es, se) through HKDF-SHA256 with fresh ephemeral keys, so later key compromise cannot decrypt past sessions.
• Mutual authentication — a transcript MAC over the handshake binds both static identities; a man in the middle cannot compute it.
• Frame sealing — ChaCha20-Poly1305 with per-direction keys, monotonically rising nonces and direction-bound AAD, plus a 4 MiB frame cap against floods.

pip install veilchat

# terminal 1 — announce on the LAN and wait
veilchat listen --name alice

# terminal 2 — find peers and connect
veilchat lan
veilchat connect 192.168.1.20 --name bob

Engineering notes

The interesting part was not the crypto — it was making asyncio behave: one listener accepts exactly one session, the handshake is written so both roles share one code path (with mirrored transcript ordering — the bug class that silently breaks handshakes), and the session layer multiplexes message/typing/ping/file frames to callbacks. UDP beacons handle LAN discovery, and the crypto, wire-format and transport layers are fully separated, so swapping TCP for WebRTC data channels touches no crypto code.

8 unit + integration tests cover key agreement, tamper detection, nonce discipline and a live two-peer exchange on localhost. MIT licensed.