Think an SSH key protected by a passphrase. Your passphrase isn't the thing that actually logs you into the server, its just what you use to unlock your actual key material you use in your SSH handshake. Your fingerprint/face identity is just your local unlock of the actual key material stored in some other secure enclave.

Your face or fingerprint being out there isn’t a concern because that’s not, ultimately, the thing being used to generate the keys or anything.

It’s an ease of use function.

On iOS for instance, as I understand it, these are being stored in iCloud Keychain. Which has a password. The derived key for iCloud Keychain is stored in such a way that the system has access if you allow biometrics to be used.

Biometrics then simply allow access, in essence, not part of the encryption process. The password for iCloud Keychain is necessary to add those items on a new device. Your biometrics aren’t stored by Apple anywhere other than in the device.

Honestly I am blown away how few people on this site understand how this stuff works. It’s fascinating and I’m surprised more people aren’t interested in understanding it. But so many people assume the biometrics are being used in the encryption process and that if your face is somehow stolen your whole life is doomed. These features have been on Apple devices for what.. a decade almost at this point? More? The process for Face ID is the same as Touch ID. Developers make zero distinction between the two in code, as that whole process is passed off to the system and effectively results in a bool value (or access to the secure item requested). At no point does a developer ever get your biometrics data.

I don’t know how Android or Windows do it but it is similar enough I suspect.

The FUD around passkeys feels like some sort of propaganda campaign to discredit it.