Use of PRF extension
Hi,
I've tried out the beta to unlock 1Password with a passkey, and it seems to work well, but I'm surprised that passkeys only serve the purpose of authentication. According to the white paper, the actual encryption key is stored on the already logged in clients, wrapped by a key provided by the server when the authentication succeeds.
This is different from the way Bitwarden has released its passkey unlock beta. The encryption key is directly derived from the passkey using the FIDO2 PRF extension. This allows the use of security keys as passkeys. I know that 1Password does support physical tokens as passkeys too, but it is not of much use, since you need a trusted device to transfer the encryption key anyway, which means you can not rely on your key as a backup method. The absence of PRF also means that users can not take advantage of the passkey backup offered by Google Password Manager and iCloud Keychain.
I think that the ability to set up PRF with supported authenticators would be a great addition to the system. It would allow a much more consistent experience and would probably prevent some account losses due to the recovery code not being saved (or access to the associated email being lost, e.g. because it was stored within 1Password). I know that not all platforms currently support PRF, but it is already quite widespread, as from what I have tried, at least Android, Chromium and YubiKeys do support it. Even users of unsupported browsers would benefit this feature since they could temporarily use a supported platform to regain access when needed.
By the way, based on my test with Bitwarden, 1Password as an authenticator (for third-party websites) doesn't seem to support PRF. This would be a great addition too, because it's the most practical way to use zero-knowledge encryption with passkey login, so we can probably expect more and more websites to implement it.
Thanks a lot for your work!
Guillaume
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