This prototype has not received an independent security audit. Deploy model services on loopback or a private authenticated link and expose only the gateway through HTTPS when remote viewers need access.

• Generate unique owner, guest, ASR, and TTS keys; do not reuse keys across roles.
• Keep .local/, environment files, model files, SSH keys, and personal ZIPs out of Git and public releases.
• The extension's manifest key is a public identity key. It is intentionally committed and is not a private signing key.
• Keep exact extension-Origin checks and the explicit server URL allowlist. A connection file must not be able to redirect a token to any arbitrary server.
• Treat fetched URLs, transcripts, model output, audio, and accent-service output as untrusted data.
• Cloud keys entered by viewers are stored in their browser profile and held in gateway session memory. The gateway is trusted with those keys. Use HTTPS remotely; never log request bodies or provider Authorization headers. Provider error bodies and validation inputs are not echoed to clients.
• The browser relay lets the gateway request only HTTPS YouTube hosts through the viewer's browser, without cookies; both the extension and the gateway enforce the host list, and the extension rejects redirects to other hosts. Only the key's own sessions use its relay.
• The desktop engine listens only on 127.0.0.1 with a random key per start; /api/file and custom provider addresses are enabled only with SYNCHRO_DESKTOP=1 and must never be enabled on a shared gateway. The desktop app stores the provider key in the user's %APPDATA%\Synchro\settings.json.
• Restrict any SSH gateway account to required forwarding ports and disallow interactive use.
• The optional CONNECT proxy accepts only HTTPS to validated public YouTube addresses and the three exact supported AI API hosts; never turn it into an unauthenticated public proxy.

The guest registry contains hashes, while connection files contain usable bearer keys. Revocation takes effect at the next authenticated request and cannot retract already delivered audio. Origin checks complement authentication; they do not replace secret keys. Anyone who has a valid key can make non-browser API requests.

For vulnerabilities, use GitHub's private vulnerability reporting if enabled, or contact the repository owner privately through their GitHub profile. Do not post exploit details, real keys, connection files, signed media URLs, or private video contents in a public issue. Describe the affected version, expected boundary, and a reproduction using dummy credentials.

If a key leaks, revoke it, rotate affected service keys, replace private connection files, and inspect your own server logs. Removing a credential from the latest commit does not remove it from repository history; avoid committing it in the first place.