Comment by OneDeuxTriSeiGo
5 days ago
> They are still susceptible to malicious enrollment. If a user is convinced a fake site is real, to the point that they are opening their password manager to copy the password to it, you should assume they will do the equivalent with a passkey (re-enroll attacker's key or register attacker's passkey).
This is only technically true because of the definition of what a passkey is is vague.
Hardware Attestation solves this problem and is "good actually". The issue with attestation is when site attempt to restrict which enclaves/sources can register keys. But if you don't restrict who/what can register keys, attestation is super useful for preventing this exact issue.
When you register your key initially you establish your hardware attestation parameters. The attacker cannot know those parameters unless they were the ones to initially register you for the site as the public attestation signature is unique per-key and the private one per-use with the public one verifying the private one.
So if you have remote attestation you can verify whether the source presenting the signature for auth is the same source that created the signature and trivially block MITM attacks. Likewise for more complicated custody/proxy chains.
This just by itself largely solves MITM key re-enrollment attacks but tech camps that support passkeys either ideologically oppose attestation (due to understandable enclosure fears) or enforce hardware attestation for enclosure purposes without bothering to address MITM/signature origin checks.
Can I do hardware attestation across several devices yet? My desktop, my phone, a console, my girlfriends phone of a different brand if I need to log into a shared account, etc?
It seems like one of those things that only works if you're sticking to one ecosystem.
Yes. You can register as many different passkeys as you want. Any limitation in passkeys registration quantity is a limitation of the website/app itself and not a limit of the spec, etc.
The spec doesn't matter. The implementation of the spec against users freedom matters.
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>Hardware Attestation solves this problem
Only in theory. Suppose you are a bank, which enclaves/sources/devices do you support vs. not support? What do you do for users on a desktop PC that don't have an enclave? Phishing sites will leverage your weakest enrollment option.
Strictly speaking it's mainly hardware attestation but it's technically "hardware based passkeys" and "remote attestation". So if you rely on attestation in general and don't restrict the attestation source it works just as well.
Software passkeys can be stolen if the client is compromised but they aren't vulnerable to MITM or phishing as long as attestation is used.
> which enclaves/sources/devices do you support vs. not support?
You support all of them and prefer the strongest configuration for the source available.
If you've registered a hardware based key with attestation and then an attack tries to intercept that via phishing or MITM, the key already has its capabilities established and if you try to use the key without attest it should fail.
If you register a key without attestation support then you may be vulnerable to MITM or phishing but you can't intercept a user/their passkey with a stronger set of capabilities and downgrade them.
Stealing passwords is already an incredibly rare attack nowadays. The attack is almost always on the cred reset path. Suppose a user loses their phone with the secure enclave and wants to login to your site using their laptop without a secure enclave.
Are you really going to block that cred reset on the grounds that it's a downgrade? You're going to have a lot of users calling your support asking why they can't login after switching devices.
So you allow it, then oops it was not a laptop, it was a phishing site.
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