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by beagle3 1487 days ago
Does this also work for the WebAuthn / U2F / TOTP use cases, or just the PGP/PIV/SSH ones?
1 comments

No. There is no way to push a value for the symmetric key that probably makes the FIDO (thus U2F / WebAuthn) feature work. You can tell the Yubikey to pick a random new one, effectively wiping your key (and rendering any credentials previously minted with it now invalid) but you can't write one over USB and this was I believe intentional.
Thanks. I will wait until it’s actually possible to create back up webauthn keys (rather than enlisting two keys with every service).
There is actually at least one fido2 device that supports backing up (mostly), based on this spec from Dicekeys https://github.com/dicekeys/seeding-webauthn

Solokeys (https://solokeys.com/ - v1, don't think the newer v2 does) have a special firmware version that implements this and allows you to use a custom seed - and as such restore a key from it. It only works on non-resident credentials (most commonly used, as the number of RKs is usually very limited) though. The firmware is here https://github.com/conorpp/solo-dicekeys/releases/tag/5.0.0 But it's also shipped in the keys dicekeys sells and I think only their app implements the client side of seeding anyway: https://www.crowdsupply.com/dicekeys/dicekeys