Passkey is some sort of specific unique key to a device allowing to use a pin on a device instead of the password. But which won’t work on another device.
Now I don’t know if that key can be stolen or not, or if it’s really more secure or not, as people have really unsecure pins.
Per Yubico’s specs on the Yubikey 4, it does not support FIDO 2 resident credentials, meaning it does not support Passkeys.
Compare to the specs of the Yubikey 5C NFC or Yubico Security Key C NFC, which both have this section:
See also Yubico blog post with an FAQ about passkeys:
I wouldn’t run out right now and buy a Yubikey to store Passkeys given the 25 key limit and the likelihood that Yubico releases a new key that supports storing far more of them, but if you do, the $25 Security Key series is the cheapest option.
Interesting, I’ll probably just have to wait till either Bitwarden supports Passkeys, or wait till Firefox on Linux supports cross-device Passkeys (so, my phone for example) as yeah a 25 key limit is not likely to be worth purchasing an upgrade for just yet.