That's not a backup, that's just another secret. If I can't record the secret onto paper that I can put in a safe deposit box at a bank (or several), then it ain't backed up.

It’s an equivalent key. It unlocks the same door. It doesn’t matter if it’s the same bits, because the only thing we care about is whether it unlocks the door.

Two different combinations for the same lock serve as backups for each other for practical purposes.

They could even be entirely different methods of access, like a Yubikey or backup codes. What matters is that you have independent ways to get in.

I understand the semantic difference but wouldn't you be able to say add a "backup" Yubikey and lock it in a safe?

Quite convenient when you need to create a new account...

No. How do you use it if it's in a safe? The only way this works is if you use the yubikey to log into google or some other auth provider and then use that auth provider for everything. But you are even worse off then as that auth provider now is a single point of failure... get that account revoked for any reason and you've lost access everywhere.

Why do that, though?

Figure out which doors you need to unlock and make sure you have at least two independent ways to get through each door. Some doors support Yubikey, so that counts as one, for those doors.

But why do THAT when what were asking for is control over our own data, our own secrets? Because it's imagined to be "less secure"?

Actually backing up keys, as in duplicating them and physically securing them, makes it simple, clear, and understandable to all involved what recovery looks like. TOTP is a great example in a similar space; my nontechnical spouse doesn't need to know "how TOTP works" to know that in case of my incapacitation she only has to read a packet of paper and follow instructions in order to perfectly recover all my accounts with zero chance of some 3rd party provider (e.g. Passkey stores like 1password/Google) having a political/technical glitch that'd get in the way of that.

Passkeys are like passwords with landlords added in. Just like with landlords for services provided, Passkeys seem very convenient for day-to-day but nightmarish in the margins and on the 5+ year scale.

My doors don’t change every other week. My set of passkeys does.

If you need (and therefore have) access to your safe every other week, chances are it’s not actually very secure.

I don't think that's really a workable solution.