Secret Notes — MVP

Zero‑knowledge note sharing. Encryption happens in the browser (AES‑GCM); the server stores ciphertext only. The URL looks like https://host/n/{id}#k=base64url(key) — the key stays in the URL fragment.

• Live demo: https://sn.1ccc.de/

Quick Start

1. Install dependencies

npm i

2. Run in dev mode

npm run dev

Open http://localhost:3000

3. Production build

npm run build
npm start

Architecture

• Client

  • Generates a random 256‑bit noteKey (WebCrypto).
  • Optional user password → PBKDF2(SHA‑256, 310k, 16‑byte salt) → passKey.
  • Final CEK = SHA‑256(noteKey || passKey), or just noteKey if no password.
  • Encrypts the note with AES‑GCM (12‑byte IV). Sends to server: ciphertext, nonce, optional salt, and metadata.
  • Shareable link: /n/{id}#k=base64url(noteKey). Password must be shared separately.

• Server

  • Stores notes table (SQLite via better‑sqlite3).
  • Endpoints:
    • POST /api/notes — create a note.
    • GET /api/notes/:id/meta — read metadata (does not consume a view).
    • POST /api/notes/:id/consume — get ciphertext and decrement views/burn.
  • Cleans up expired notes every 10 minutes.
  • Security headers: CSP, HSTS, Referrer‑Policy: no-referrer.
  • Rate limiting: 60 requests/min per IP for /api/*.

Parameters

• Expiration: default 24 hours, up to 30 days.
• Burn after read: delete on the first consume.
• View limit: if reached, note is deleted on consume.
• Extra password: client‑side only; server stores salt only.

Security Notes

• The server never sees the key or the password.
• URL fragment (#k=...) is not sent to the server; Referrer‑Policy prevents leaks.
• AES‑GCM with 96‑bit IV; key length is 256‑bit.
• PBKDF2 is used temporarily for the MVP. Argon2id is recommended long term.

Migrating PBKDF2 → Argon2id (post‑MVP)

1. Add Argon2id in the browser (e.g., argon2-browser or @noble/argon2 when stable).
2. In deriveCombinedKey:
   • passKey = Argon2id(password, salt, { t=3, m=64MB, p=1, hashLen=32 })
   • combined = HKDF‑SHA256(ikm = noteKey || passKey, salt = '' , info = 'secret-notes', len = 32)
3. Mind CSP: you may need wasm-unsafe-eval and/or a worker.

MVP Limitations

• “Burn after reading” happens at consume, not after successful decryption (the server cannot know decryption outcome).
• If the password/key is wrong, a view is still consumed. The user is shown an error.

Contributing

Feel free to submit a pull request or open an issue if you have any suggestions or improvements.