Device pairing spike

Enrol a new device with no password: the new device makes an ephemeral keypair, an already-unlocked device wraps the master key to it, and only ciphertext crosses the gap. Proves the whole chain — the new device ends up able to read an encrypted note it has never seen the key for.

Open this page twice (two tabs, or two devices) and use the left panel on one and the right panel on the other. Payloads move by copy-paste here; production carries the public key in a QR code. Either way the fingerprint comparison is the security control, and that works identically.

Device A — already has the key

No master key yet.

2 · Paste Device B's public key:

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Send this to Device B:

Device B — being enrolled

Send this to Device A:

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2 · Paste the wrapped bundle from Device A:

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Verdict

Run Device B step 1, then work left-to-right.

What counts as success: Device B decrypts the note using a key it never possessed and that never crossed in the clear. What to watch: the fingerprints on both panels must match before you approve — that comparison is what stops a relay substituting its own key and receiving the master key. Worth running once in Firefox, since this is the path that supports it without PRF.