Why your key never leaves your browser

When you create a configuration, the private key for it is generated inside your browser, using the browser's own cryptography (X25519 in Web Crypto). What leaves the page is only the matching public key — the half that cannot be turned back into the private one.

What follows from that, mechanically rather than as a promise:

• We cannot hand your key to anyone, because we never had it.
• We cannot leak it in a breach, for the same reason.
• We cannot rebuild your configuration — which is why the file is shown once and must be downloaded before you leave the page. Losing it is not a disaster: revoke the device and create a new configuration.

The one requirement: a browser with X25519 support in Web Crypto. Every current Chrome, Firefox, Safari and Edge has it. A browser that lacks it is told so plainly — the page refuses rather than falling back to generating the key somewhere weaker, because a fallback would silently break the property this page is named after.