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New storage scheme

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This commit is contained in:
mirai
2026-01-06 21:42:50 +08:00
parent 264d19e932
commit 467d942877
9 changed files with 1287 additions and 23 deletions
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README.MD
+37 -10
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@@ -29,37 +29,66 @@ every "secure" messenger still stores metadata somewhere. this doesn't. it's jus
│ │─────── POST /srp/init {username, A} ───────► │ │
│ │ (A = client public ephemeral) │ │
│ │ │ │
│ │◄────────── {user_id, B, salt} ────────────── │ │
│ │◄──── {user_id, B, salt, room_salt} ───────── │ │
│ │ (B = server public ephemeral) │ │
│ │ (room_salt = E2E key derivation) │ │
│ │ │ │
│ │ [client derives room_key via HKDF: │ │
│ │ room_key = HKDF(password, room_salt)] │ │
│ │ │ │
│ │ [both sides compute shared session key │ │
│ │ [both sides compute SRP session key │ │
│ │ using password + ephemeral values] │ │
│ │ │ │
│ │ │ │
│ │─────── POST /srp/verify {user_id, M} ──────► │ |
│ │─────── POST /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] │ |
│ │ [MITM can't derive session key] │ │
│ │ │ │
├──────────────────────────────────────────────────────────────────┤
│ ENCRYPTED CHAT │
│ E2E ENCRYPTED CHAT │
├──────────────────────────────────────────────────────────────────┤
│ │ │ │
│ │═══════ WebSocket /ws/chat?user_id ═════════► │ │
│ │ (authenticated session) │ │
│ │ │ │
│ │◄═══════════ AES-encrypted messages ════════► │ │
│ │ (Fernet = AES-128-CBC + HMAC) │ │
│ │ │ │
│ ┌─┴─┐ ┌──┴──┐ │
│ │ C │──── encrypt(msg, room_key) ───────────►│ S │ │
│ │ L │ │ E │ │
│ │ I │◄─── ciphertext (broadcast) ────────────│ R │ │
│ │ E │ │ V │ │
│ │ N │ decrypt(ciphertext, room_key) │ E │ │
│ │ T │ │ R │ │
│ └─┬─┘ └──┬──┘ │
│ │ │ │
│ │ [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 │ │
│ │ │ │
│ │ [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.
@@ -67,8 +96,6 @@ every "secure" messenger still stores metadata somewhere. this doesn't. it's jus
## install
```bash
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
```