Mars

Well, it’s a full keypair being stored: Authenticators like Bitwarden need to first provide the public key to the relying party (RP) so the RP can issue the encrypted auth challenge. The challenge then is handed back to the authenticator, user verification happens, then the challenge is signed by the private key and sent back to the RP for verification to complete the auth ceremony.

Article links to 1Password’s directory of passkey supported sites/apps.

You’re thinking about “device-bound passkeys”. Bitwarden and any other third-party credential manager leverages “synced passkeys” because they don’t control the hardware.

Synced passkeys are actually called out in the FIDO Alliance’s FAQs as preferred since they more closely align with the desired replacement of traditional passwords.

It’s an interesting thought to consider that without access to centralized distribution platforms like app stores, something incredibly similar is created in its place: The so-called “super-app” (e.g. WeChat, Alipay).

This is the way