Pass the Passkey: A Novel Attack Surface in Passwordless Authentication

This is someone related to a major TPM pet peeve of mine: the TPM only really cares about global device state and has no concept that a device may be a multi-user system, have multiple processes with different security levels, have multiple tenants, etc.

For example, it really ought to be possible to seal a secret such that it can only be unsealed if PCRs have certain values (the usual TPM thing) and the requester of the unseal operation is tagged by the OS (software TCB) as having a certain identity. The latter part is entirely missing from the TPM spec. (The identity could be a hash of the process, just a UUID, or just about anything else as long as it was reasonably well associated with the process in question. Obviously there are subtleties here.)

If the TPM worked the way I wanted, an unprivileged process running alongside Chrome would be completely unable to use the TPM to pretend to be Chrome.

These are endpoint malware attacks, not attacks on Passkeys per se. This is already a game-over position for an attacker to be in.

>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?

Boy I’m so tired of people trying to make clever attack names. They don’t help remember things, there are too many.

So all 3 “pass-ta-key” attacks are not attacks on passkeys, they’re attacks on the Google vault.

And if you get access to the vault, then you get everything. OK. And if you get access to a synced traditional password vault, then you get everything.

So… meh. These are bugs, they will be fixed. Good on them for disclosing them. But this does not prove that passkeys are terrible. This does not make them less secure than random passwords.

If it wasn’t for the fact that they just happen to be getting passkeys, seems like this wouldn’t be worth a headline or discussing at all. And if they have this level of access, then they also get all the standard password credentials in the vault too, right?

"You must enable DRM to play some audio or video on this page" pops up in the strangest places...

It is hard to find the content for all of the glitzy ads on this site.

It seems like I have to trust more things that aren't very intuitive and are out of my control for passkeys to really be secure. For passwords, I only need to trust myself. I trust that I don't lose them, don't re-use them, and don't fall for phishing attacks.

Of course I also have to trust that whatever service I'm authenticating to does their part correctly, but that's the same either way.

I'm going to continue to use passwords.