csuwldcat

Yes, this is true, however, that means an external actor is able to execute arbitrary code in your origin, so they could also trick the user into signing malicious payloads with even the native passkey itself. There's more downside to exfiltration here, but having arbitrary code from an external party executing in your page is a more general cause for concern you'd need to mitigate regardless.

Hmm, can you provide further details? I'm using it on Android in Chrome and Brave, and it works fine.

That would either mean you have arbitrary, malicious code executing in the bound origin (the origin was hacked and shipped malicious code), or you allowed random callers externally to take signatures out of the boundary - don't do either of these things, they are verboten. The whole point is that for the passkey you use as a PassSeed, you never do any signing other than locally for ECDSA recovery.

You can run the PassSeed code/mechanism on your own domain or localhost to ensure it's not subject to malicious host exfiltratuon. I agree that one should only trust a foreign host with low-security uses under this scheme.

A roaming authenticator does not have access to a CTAP mechanism to query the platform’s credential store. CTAP defines how the platform queries a roaming authenticator, in that direction. There is no CTAP command whereby an authenticator queries the platform for 'all passkeys you have' because the platform is the client in its protocol model. Platform / synced passkeys managed by the OS are not present on the roaming authenticator, so credential management APIs invoked from the roaming authenticator cannot enumerate them (it can only enumerate what it stores).

There's also the specific case of synced passkeys, which aren't exposed to CTAP management APIs for external parties, only to the OS/platform itself. You seem tied to a narrative where a user can install a native app that gets permission to call core OS/platform APIs that let the app get all the public keys of passkeys on the device, but no such permissions/APIs exist for apps, and providing them would be in explicit violation of the fundamental security model. In reality, only the platform/OS and highly trusted actors/components that are already within the existing trust model have such access for internal purposes, and if that's not a safe assumption, it would have broader implications beyond this concern.

It's not just about the WebAuthn API, you're talking about passkeys as if their key bundles are freely accessible to random userland actors, which is absurd. If that were the case, many assurances the platform makes would be out the window. The reality is that you are obviously already trusting the platform, hardware, its software/firmware, and the implementation's use of core key management APIs, which it doesn't just offer up to random callers. If you think any of those components/actors are not adhering to fundamental boundaries/limitations, like exposure of sensitive credential material to random callers on the device, it's a more far reaching indictment of passkeys in general.

The underlying CTAP implementations are only used by the platform to facilitate core activities, they are not used to expose key pairs to external parties. Please link to where any API offers up public keys to external userland actors, and any use of said APIs beyond core credential management. If this is assumed insecure/exposed, it would mean the system and its guarantees cannot be trusted as advertised, given both keys are supposed to be handled as a secure, opaque bundle, disclosed to no one beyond the bound origin at create time.

No need for the "oh dear"-ing before you provide evidence. I'm not aware of any command for fetch or enumeration of public keys in CTAP (was rather confident it doesn't provide any such thing). Care to link to what you were referring to?

It's a deliberate architectural decision that passkey authenticators not allow any retrieval or enumeration of key pairs - they don't even have internal APIs for it. This holds true for all known implementations, as it is a core principle of the system design.

The interesting thing about Passkeys is that they are only ever output in the client create() call, and the platform does not retain them for disclosure after that, so if you don't send them out of the origin boundary, they are treated like a virtually secret value by the platform. It's ironic, because the WebAuthn/Passkey authors (who I know some of) explicitly treat the public key as a sensitive value, and built system assumptions around that, which is what makes this possible. It's a rather gross hack, can't deny it that, but there are a group of use cases for which it is a better fit than any of the far more ugly flows many non-P-256 self-custodied key use cases are accomplished with today.