🤐 CMD-CHAT

encrypted terminal chat. no servers. no logs. ram only.

---

peer-to-peer encrypted chat that runs in your terminal. you host, you control. close the window — everything's gone.

why

every "secure" messenger still stores metadata somewhere. this doesn't. it's just two terminals talking over an encrypted tunnel. nothing written to disk, ever.

how it works

┌──────────────────────────────────────────────────────────────────┐
│ SRP AUTHENTICATION │
├──────────────────────────────────────────────────────────────────┤
│ │
│ CLIENT SERVER │
│ │ │ │
│ │══════════════ TCP CONNECT ══════════════════►│ │
│ │ │ │
│ │─── {"cmd":"srp_init","username","A"} ──────► │ │
│ │ (A = client public ephemeral) │ │
│ │ │ │
│ │◄──── {"user_id","B","salt","room_salt"} ──── │ │
│ │ (B = server public ephemeral) │ │
│ │ │ │
│ │ [client derives room_key via HKDF: │ │
│ │ room_key = HKDF(password, room_salt)] │ │
│ │ │ │
│ │─── {"cmd":"srp_verify","user_id","M"} ─────► │ │
│ │ (M = client proof) │ │
│ │ │ │
│ │◄──────── {"H_AMK","session_key"} ─────────── │ │
│ │ (H_AMK = server proof) │ │
│ │ │ │
│ │ [password never transmitted] │ │
│ │ [MITM can't derive session key] │ │
│ │ │ │
├──────────────────────────────────────────────────────────────────┤
│ E2E ENCRYPTED CHAT (same socket) │
├──────────────────────────────────────────────────────────────────┤
│ │ │ │
│ │◄─────── {"type":"init","messages","users"} ─ │ │
│ │ │ │
│ ┌─┴─┐ ┌──┴──┐ │
│ │ C │─ {"type":"message","text":encrypted} ─►│ S │ │
│ │ L │ │ E │ │
│ │ I │◄── {"type":"message","data":{...}} ────│ R │ │
│ │ E │ │ V │ │
│ │ N │◄── {"type":"user_joined",...} ─────────│ E │ │
│ │ T │ │ R │ │
│ │ │◄── {"type":"user_left",...} ───────────│ │ │
│ └─┬─┘ └──┬──┘ │
│ │ │ │
│ │ [server stores ONLY ciphertext] │ │
│ │ [server CANNOT read messages] │ │
│ │ [all clients with same password │ │
│ │ derive identical room_key] │ │
│ │ │ │
│ │ Encryption: Fernet (AES-128-CBC + HMAC) │ │
│ │ Key derivation: HKDF-SHA256 │ │
│ │ Protocol: newline-delimited JSON over TCP │ │
│ │ │ │
│ │ [on disconnect: keys wiped from RAM] │ │
│ │ │ │
└──────────────────────────────────────────────────────────────────┘
┌──────────────────────────────────────────────────────────────────┐
│ KEY HIERARCHY │
├──────────────────────────────────────────────────────────────────┤
│ │
│ password ──┬──► SRP ──► session_key (per-user, auth only) │
│ │ │
│ └──► HKDF(password, room_salt) ──► room_key (shared) │
│ │
│ room_salt: generated once at server start │
│ room_key: deterministic, same for all clients with same pwd │
│ │
└──────────────────────────────────────────────────────────────────┘

SRP (Secure Remote Password) — password is never sent over the network. both sides prove they know it via zero-knowledge proof, then derive identical session keys.

install

git clone https://github.com/emilycodestar/cmd-chat.git
cd cmd-chat
python -m venv venv &&source venv/bin/activate && pip install -r requirements.txt

windows:

python -m venv venv ; .\venv\Scripts\activate ; pip install -r requirements.txt

usage

start server:

python cmd_chat.py serve 0.0.0.0 3000 --password mysecret

connect:

python cmd_chat.py connect SERVER_IP 3000 username mysecret

features

• ram only — nothing touches disk
• pure sockets — no http, no websocket, just raw tcp
• srp auth — password never sent over network
• e2e encryption — Fernet (AES-128-CBC + HMAC)
• zero dependencies on web frameworks — only asyncio

license

MIT