# 09 — Pairing, Auth & Security

## 9.1 Threat model

- **Trusted domain:** a personal agent on the user's own machine; one owner, a
  few of their own devices (phone + desktop).
- **Primary risks:** (a) an unauthorized device connecting to the WS and
  reading/driving the agent; (b) eavesdropping on the WS in transit; (c) token
  leakage in logs; (d) arbitrary file read via media pull.
- **Not addressing (v1):** multi-tenant isolation, adversarial multi-user abuse,
  E2E encryption.

## 9.2 Pairing flow

1. **Generate a token.** `hermes gateway setup` (our `interactive_setup`) either
   uses an existing `ANDROID_TOKEN` or generates a fresh high-entropy token
   (e.g. 32 bytes → 64 hex chars) and stores it in `.env`.
2. **Present to the app.** Two options:
   - **QR code:** the setup prints a QR encoding
     `iris://pair?host=<lan-ip>&port=8790&token=<token>` (or a WSS URL). The
     phone scans it with the app's camera (or a system scanner) → pre-fills
     settings.
   - **Manual:** user types the server URL + token in the app's Connect screen.
3. **App connects.** First WS frame is `hello {token, device_id, device_name,
   caps, fcm_token?}`.
4. **Server verifies.** Constant-time compare of `token` vs `ANDROID_TOKEN`
   (`hmac.compare_digest`). Optionally check `device_id` against
   `ANDROID_ALLOWED_USERS` (if set) or `ANDROID_ALLOW_ALL_USERS`.
5. **On success:** register the device in `devices.db`, send `hello.ack`.
   **On failure:** send `error {code:"auth"}` and close.

`device_id` is a stable, app-generated UUID (persisted in the app's
secure storage). It identifies the device for routing + push, **not** as a
security principal (the token is).

## 9.3 Auth model

- **Token = the security principal.** Any connection presenting the valid
  `ANDROID_TOKEN` is authorized (it's the user's own token).
- **Allowlist (optional):** `ANDROID_ALLOWED_USERS` (comma-separated
  `device_id`s) restricts which *devices* may connect even with the token —
  useful if the token is shared. `ANDROID_ALLOW_ALL_USERS=true` disables the
  allowlist (dev only).
- **Per-device tokens (stretch):** mint a unique token per device at pairing
  (revocable) instead of one shared token. v1 uses the shared token + optional
  device allowlist.
- **Re-pairing:** rotating `ANDROID_TOKEN` invalidates all devices; they must
  re-pair. `hermes android pair` (stretch CLI) re-issues + prints a new QR.

## 9.4 Transport security

- **Default (LAN/dev):** plain `ws://` on the trusted LAN. Fine for a home
  network.
- **WSS (recommended for remote):** set `ANDROID_WS_CERT` / `ANDROID_WS_KEY`
  (self-signed or CA-signed). The app pins/accepts the cert (self-signed → user
  confirms fingerprint on first pair, like a SSH host key). 
- **Remote reachability options** (documented, user's choice):
  - **Tailscale / WireGuard** (recommended): gateway gets a stable tailnet IP;
    app connects over the private mesh. No public exposure.
  - **Reverse proxy / tunnel** (Caddy, Cloudflare Tunnel, ngrok): terminate TLS
    at the edge, forward WS to `127.0.0.1:8790`.
  - **Public bind** (`0.0.0.0`) + WSS + strong token — last resort.
- The app stores the server URL + (for self-signed) the pinned cert fingerprint
  in secure storage.

## 9.5 Secret & PII handling

- **Tokens/keys never logged.** Redact `ANDROID_TOKEN`, FCM tokens/keys, ntfy
  tokens in all log output (hermes PII policy; `agent/redact.py` patterns).
- **`device_id`** is a random UUID (not PII). `device_name` is user-chosen.
- **Media pull** is gated by hermes `validate_media_delivery_path` + delivery
  root/recency/denied-path checks (`gateway/platforms/base.py:1684`) — the
  plugin can only serve files hermes is allowed to deliver (no arbitrary file
  read).
- **Search** is local-only (user's own hermes home); no data leaves the machine.

## 9.6 Profile safety

- All plugin state lives under `get_hermes_home()/"android"` (profile-aware).
- Secrets are read with the scope-aware `_get_scoped_secret` pattern (see
  `plugins/platforms/irc/adapter.py:42`) so multiplexed profiles don't leak
  each other's tokens (fail-closed under `gateway.multiplex_profiles`).
- The WS bind uses a scoped lock (`gateway.status.acquire_scoped_lock`) so two
  profiles can't bind the same port/identity.

## 9.7 Hardening checklist

- [ ] Constant-time token compare.
- [ ] Bounded per-connection send buffer + rate limit on inbound frames.
- [ ] Reject oversized frames / uploads (`max_upload_bytes`).
- [ ] Verify media sha256 + re-sniff MIME (don't trust client).
- [ ] Redact all secrets in logs.
- [ ] WSS + cert pinning for remote.
- [ ] Outbox retention cap + prune.
- [ ] Fail-closed secret reads under multiplexing.