Re: [webauthn] Device-bound key extension (#1658)

@timcappalli @agl Ah, I see, thanks for explaining. So what I missed is that `dpk` is not dependent on `synced cred` alone, but on `synced cred + context` - and that `context` may fluctuate in strength over time, so `dpk` can be a more reliable alternative to `synced cred + context`.

@equalsJeffH I wasn't actually thinking that a `navigator.credentials.create()` operation would be necessary for generating `AttObjForDevicePublicKey` - I reckon the authenticator could just as well construct that object during a `navigator.credentials.get()` operation. And the AAGUID is already included in the [attested credential data](https://www.w3.org/TR/2021/REC-webauthn-2-20210408/#attested-credential-data), so that would also be signed over in every attestation statement format.

But on that note, I suppose one complication with my suggestion is that `AttObjForDevicePublicKey.attObj.authData` would probably just be a copy of the top-level authenticator data for the "dpk registration" ceremony? Which was likely a `get()` - meaning you'd have a `get()` authenticator data with an `AT=1` flag and including attested credential data, which might end up breaking implementations more than the polymorphic verification procedure would. Unless the `AttObjForDevicePublicKey` gets its own, separate `authData` so that the top-level authenticator data can remain unchanged. But yeah, this idea might end up being a net increase in complexity.

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Received on Tuesday, 10 August 2021 17:06:00 UTC