>4. Using the hash of that handshake, the attacker interacts with the victim’s TPM and uses the extracted identity key to sign the handshake hash together with the assertion request

Huh? If you have this level of local privileges you can just read session cookies from the browsers store? I guess stealing all the keys is notable, but you can manipulate any password manager with this level of access right?

What's the threat model here, that synced passkeys should be secure in even in situations involving compromised clients? How?

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Gigachad 29 minutes ago | parent | next [-]

>that synced passkeys should be secure in even in situations involving compromised clients?

I think that is the idea actually. By using secure hardware features it is in theory possible to secure the passkeys even in the case of compromised clients. Like how the iphone uses a security coprocessor to store the decryption keys and face id info out of the reach of iOS.

But this isn't overly concerning since it's still at a minimum as secure as passwords in a local compromise situation.

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ted_dunning an hour ago | parent | prev | next [-]

It's not that simple. The stolen file has no clear text passwords and ideally, these passwords can only be decrypted on the right hardware with user confirmation. Of course, eternal and repeated confirmation requests are an anti pattern all their own, but the cloud attestation service not verifying the hardware sounds like a really glaring omission.

	▲	colemannugent an hour ago \| parent [-]
		It kinda is. If they use Chrome and it's cloud backed password manager, odds are they use GMail. That plus full access to a trusted device (which you have in this scenario) allows you to change their Google account password. Boom, full persistence. I can think of at least a dozen easier ways to do nefarious things with this level of access that are at least that simple. As an example, faking user attribution would be trivial. How could Google patch this? If the client is compromised and the attacker can manipulate the local TPM or it's equivalent there's no defense.

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vel0city an hour ago | parent | prev [-]

At least for accounts you want to keep very secure, session cookies are probably very time-limited. Stealing a passkey ensures persistent access in the future.

But I largely agree, if they're able to do this on your system you're already hacked and they can do a ton of very bad things.