Comment by tomxor | Hacker News Reader

Comment by tomxor | Hacker News Reader

Yubico have a verification page for this purpose: https://www.yubico.com/genuine/

In theory this is enough to prove it's genuine because they are supposed to be tamper-proof, i.e even if you buy indirectly or it's intercepted in transit.

The only thing I can see this failing to detect is an intermediate layer that intercepts USB and has access to the physical button... e.g If an attacker embedded a genuine small form-factor key into a larger package that mimics a larger form factor. This would be useful to an attacker which could get a target to trust the key, believe it's genuine and start associating it with services, and then be able to remotely activate it once they have gained the users trust... still a tough challenge to pack all of that with wifi etc into a small enough package with a micro yubikey or something inside.

I don't think this is a very realistic possibility currently, but if you are concerned, you could simply buy the smallest possible yubikey form factor.

The attack you're describing doesn't require wifi. If the victim visits the attacker's page, the attacker page is free to request signatures (also non-presence-attesting signatures) from the key. This can be used to send data to the key (in the nonce) and from the key (the signature is nondeterministic). I don't know if this can be done without user's awareness in the new web api for security keys, though.

How can it protect from cloned hardware? Ie. they get keys, clone them, sell at discount - and sell shipment address + software/hardware backdoor on the side.

Whoever cloned the hardware would need to know the private key Yubico embed in it, and those aren't east to extract, although presumably feasible for cutting edge chip reverse engineering labs.

Or whoever manufactured the Yubico chip in the first place.

That's infineon for the latest generation:

http://www.hexview.com/~scl/neo5/

I wonder if you could mitigate that by manufacturing them without a private key and then have Yubico themselves program the keys (in one-time programmable memory) before shipping to the customer.

Here's an example from 2018 of someone trying to extract secrets from a Yubikey. https://duo.com/labs/research/microcontroller-firmware-recov.... Seems they don't get very far. Or it's at least very laborious. But as you say, who knows what a cutting edge lab can do. Skimming the web, it seems like people have had more success with things like Google Titan keys.

That's not a yubikey but a standard pic microcontroller not designed for security applications.

And as far as I understand he's now describing his methods there rather than particular attempts?

There's a bit about Yubikey at the very end of the article.

If you are interested in this topic, the physical security chapter of Ross Anderson's Security Engineering has a nice intro. The second edition is free online https://www.cl.cam.ac.uk/~rja14/book.html

Out of curiosity, why are keys not generated upon first run? Why is there something to extract out of a brand new YubiKey to begin with?

For FIDO, which was the main topic of the original post, the Yubikey has a symmetric key inside it.

Choosing a random new key invalidates all your existing credentials enrolled with that Yubikey, since your Yubikey will no longer be able to decrypt the identifier provided and sign proof that it knows the associated private key (in practice what it decrypted was your private key for that account, and now it can't do that)

This "reset" operation is supported on Yubikeys, and you perhaps should do it when you get the key (Don't do it now! It invalidates your credentials as I described!), although most users probably don't. However, even if you do this if your key is fake why would the initialisation actually work? The same adversary could modify it to just ignore this reset attempt and use a symmetric key they know. So there is no benefit from hypothetically requiring you to perform this initialisation step, nor from having the device do it when first used.

To do FIDO the Yubikey has a symmetric (typically called "secret" but here it isn't really functioning as a secret since nobody else knows what it is) key but not a private key baked inside it.

Hiding such symmetric keys (typically AES) from adversaries with fairly large budgets who have physical access to your device is already a thing. Would I bet my life on it if I was Edward Snowden? Maybe not. Am I comfortable with this for securing a bank account with my life savings in it? Yes.

Thanks for that link didn't know about that. Helpful since I got mine off Amazon which as we all know has occasional uhm issues

I like how you uhm issues, but not occasional.

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