I assumed you need consent to receive PII, full stop. Again IANAL, but I assumed saying you don't do anything at all with the PII you receive doesn't exempt you from anything under GDPR. I may be wrong, though I hope not to be.
IANAL but European law is nuanced over whether IP addresses are PII. If I'm not mistaken it's been ruled they are for ISPs, rationale being they have enough other data points that once correlated with IP addresses allow to identify individuals. Whether the same applies to Google (I suppose) is definitely not clear to me.
> To be clear, the key can never leave the TPM (with how tpm-fido is implemented).
Yep sorry you're right you wouldn't get the actual keys to use elsewhere, you can just use them as if you had them on the "compromised" device only, my bad.
> But it doesn't really matter for the Webauthn threat model. An attacker with root access can steal your browser sessions directly.
If you're using WebAuthn to authorize the emission of session tokens you're absolutely right, just get root and steal them from the browser :) but WebAuthn is more versatile than that. You could e.g. require a WebAuthn assertion to authorize a payment. In that case root access still doesn't help you with a secure enclave, but is sufficient to trick your server in believing the user has authorized the operation with tpm-fido, right? Again I absolutely don't mean to detract from tpm-fido, just pointing out that, very sadly, I don't think a TPM+fingerprint reader+software can really replace integrated solutions like Apple's secure enclave, or a yubikey, etc.
In general unless I'm mistaken, it's not a tpm-fido shortcoming specifically.
Isn't this approach significantly less secure than Apple's though? As far as I understand the secure enclave coprocessor in Apple devices stores key material and implements user verification (TouchID etc.), right? Instead software like tpm-fido bridges (in software) a user verification mechanism (maybe even a fingerprint reader) and the system's TPM. But such a system can be interposed with mere root access, and the TPM tricked in giving out its secrets, no? Please correct me if I'm getting it wrong, but Apple's approach is instead resistant even to full kernel compromise, precisely because the communication between TouchID/FaceID and the secure enclave cannot be interposed.
I'm a tpm-fido user myself by the way, thank you psanford!