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Getting a biometric security key right

yubico.com

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Re: Getting a biometric security key right

#31

Post by ryukafalz »

xaduha wrote: post #30
ryukafalz wrote: post #29

Earlier quoted context omitted.

How does gnupg interact with contactless cards? I know for a contact smartcard if I try to perform an operation with the card not present, I get a prompt to insert the card, and then I get a prompt to enter the PIN when inserting the card and continuing. A contactless card in a ring form-factor is unlikely to be on the reader for long, though... is gnupg aware of contactless readers and will it e.g. ask for your PIN…

If you have experience with contact cards, then it's all the same as far as end applications are concerned, it's abstracted away. > is gnupg aware of contactless readers and will it e.g. ask for your PIN without the card being present and then prompt you to tap the card? No, it will behave as if there's no card/ring if you don't have it around the reader. Software polish is a weak point, e.g things like `ssh-add -s /…

Ahh, interesting. I suppose then testing when it’s possible to insert/remove a contact card without disruption would give me a good idea of what to expect from a contactless card.

Thanks for the info!

EDIT: It seems like requesting a decryption, removing/inserting a Yubikey while the pinentry screen is up, then entering the PIN does not work. I suppose I've broken the session then. So I'm guessing to use a ring form-factor card, I'd have to keep the ring above the reader during the whole operation, which means I'd have to remove it to place on the reader and can't just keep it on/tap when needed.

Hm. That's a bit unfortunate.

(Also possible the Yubikey behaves differently as it's both reader and card in one... I don't have a dedicated reader set up to test with at the moment.)

EDIT 2: For anyone who comes across this later: no, a dedicated reader behaves the same way; once the pinentry prompt is open, you can't remove the card and reinsert without invalidating that request.

Re: Getting a biometric security key right

#32

Post by xaduha »

ryukafalz wrote: post #31
xaduha wrote: post #30

Earlier quoted context omitted.

If you have experience with contact cards, then it's all the same as far as end applications are concerned, it's abstracted away. > is gnupg aware of contactless readers and will it e.g. ask for your PIN without the card being present and then prompt you to tap the card? No, it will behave as if there's no card/ring if you don't have it around the reader. Software polish is a weak point, e.g things like `ssh-add -s /…

Ahh, interesting. I suppose then testing when it’s possible to insert/remove a contact card without disruption would give me a good idea of what to expect from a contactless card. Thanks for the info! EDIT: It seems like requesting a decryption, removing/inserting a Yubikey while the pinentry screen is up, then entering the PIN does not work. I suppose I've broken the session then. So I'm guessing to use a ring form-…

BTW if you decide to buy a contactless reader steer clear of acr122u, they pop up first in the search results and either fake or bad or both.

Research before you buy, don't look for NFC, looks for contactless PC/SC

https://ccid.apdu.fr/#readers

http://nfc-tools.org/index.php/Devices_compatibility_matrix

https://webshop.d-logic.net/nfc-rfid-device-comparison

Re: Getting a biometric security key right

#34

Post by tialaramex »

hpfr wrote: post #25
ecesena wrote: post #22

Earlier quoted context omitted.

FIDO2 supports password-less and username-less authentication, both as a single factor, i.e. no passwords. Password-less is like 2FA but without the first factor. You type in your username, next you use the security key. Username-less is done via resident keys, that can also store the username at registration. The whole experience is just authenticating with the security key. If you use FIDO without a password (not a…

If you have two, say, Microsoft accounts, can you use the same FIDO2-capable authenticator for both, and can Microsoft correlate the accounts by authenticator? I know keys are unique per-site, but are they per-account? edit: The spec[1] is vague on this, but it looked like a Relying Party can't correlate accounts directly via some kind of identifier for the authenticator. It looks like individual key pairs are genera…

Yes, all normal sites should allow you to use WebAuthn without attestation and should default to switching it off. Apple's guidelines recommend enabling it, but that's bad advice.

Attestation only makes sense if you'd actually reject authenticators you don't trust, which might make sense if you're the Foo Corp. Corporate System and you only trust genuine Important Security Inc. authenticators because you issued one to every employee and so that's another safeguard against attack (it prevents employees sidestepping security like those webcams showing an OTP key output). But for a public site and especially if you actually offer other less secure alternatives (like SMS or TOTP) it makes no sense to even ask what type of authenticator I'm using. I always tell Firefox to refuse to answer.

However, the attestation certificate in that x5c field isn't a unique identifier. So basically Microsoft learns that these two users have bought the same brand and maybe (if that brand sells enough volume to make it worth changing out the EPROM or whatever in batches) the same batch, but it's supposed to be at least 10 000 different authenticators sharing "your" attestation.

Re: Getting a biometric security key right

#35

Post by ecesena »

hpfr wrote: post #25
ecesena wrote: post #22

Earlier quoted context omitted.

FIDO2 supports password-less and username-less authentication, both as a single factor, i.e. no passwords. Password-less is like 2FA but without the first factor. You type in your username, next you use the security key. Username-less is done via resident keys, that can also store the username at registration. The whole experience is just authenticating with the security key. If you use FIDO without a password (not a…

If you have two, say, Microsoft accounts, can you use the same FIDO2-capable authenticator for both, and can Microsoft correlate the accounts by authenticator? I know keys are unique per-site, but are they per-account? edit: The spec[1] is vague on this, but it looked like a Relying Party can't correlate accounts directly via some kind of identifier for the authenticator. It looks like individual key pairs are genera…

You have to distinguish between resident keys and non-resident keys (that I'll just call "normal keys").

Resident keys are stored on the device, so today you can only have a limited number of RKs. This said it's a temp limitation. As usage will increase, devices will allow for more RKs. For example, if I'm not wrong, yubikeys support 25 RKs, solokeys 50. (But the only sites where you can use RKs are basically Microsoft or demos.)

For each account on a given site, you'll have an independent RK. (I don't believe you can have 2 RKs for the same account on the same device, but that's an implementation detail.)

Normal keys, instead, are generated on the fly. They are not stored, so a single device can support unlimited sites and accounts. When you enroll a device in, say, your primary Google account, trying to enroll the same device again produces the same cryptographic key. So, in fact, for each account you can only have one key per device. But you can have unlimited accounts times unlimited sites on a single device.

If you have 2 accounts on the same site on the same device, you're correct in saying that the site can't link the 2 accounts to the same device. In addition, on the device there's nothing stored, so even someone with access to the device (say, border control) can't see what sites you used the device with. Important: this is only for non-resident keys.

I can't predict the future, but my expectation is that we'll see adoption of RKs for username-less login, and non-RKs for 2FA. I personally don't particularly like RKs for privacy reasons, but the specs seem to prefer them (and the UX seems much better). See also this: https://twitter.com/0x0ece/status/1160627435668480000

Re: Getting a biometric security key right

#36

Post by xaduha »

With Yubico I always get a feeling that if they could breakaway from all this legacy smartcard stuff and lock everyone in, they would. But they can't yet, so they distanced themselves from it and were keeping it on the down-low ever since.

I would really like if they made a wearable without any ports like a NFC ring, but that would mean either keeping it tied to phones only with an app or selling their own NFC/contactless reader, most likely with some proprietary bent.

Re: Getting a biometric security key right

#38

Post by nullc »

Ottolay wrote: post #10
dheera wrote: post #5

A true biometric key would allow authentication from any key and not just a registered key, otherwise it just degrades into a possession authentication factor. A true biometric key would allow you to walk around with absolutely nothing, and doing 2FA using only what you know (password) and what you are (your finger). Is that possible with this? Could I e.g. pass 2FA on my accounts on a friend's computer using their k…

The problem is that your fingerprint is really just a set of information attached your body, similar to a long static password. Not very secure and you can't change it if it was compromised. The fingerprint on the yubikey is really just a possession check for the yubikey in case it was stolen. The main protection comes from the asymmetric cryptography inside the yubikey.

> The fingerprint on the yubikey is really just a possession check for the yubikey in case it was stolen.

And one that only depends on the tamper-resistance of the hardware.

It's possible to use error correcting codes to extract deterministic secrets from fuzzy data like fingerprints, but no one (virtually no one?) implements that.

Instead, the fingerprinte reader has some cleartext fingerprint fingerprints that it compares the fingerprint to and just makes an accept/reject decision. Extract that data and you can make an acceptable input, or glitch the processing and you can just bypass it.

Presumably it's better than the button that literally any touch activates, but I think a conservative security analysis would pretty much just treat it like a button.

Re: Getting a biometric security key right

#39

Post by tialaramex »

ecesena wrote: post #35
hpfr wrote: post #25

Earlier quoted context omitted.

If you have two, say, Microsoft accounts, can you use the same FIDO2-capable authenticator for both, and can Microsoft correlate the accounts by authenticator? I know keys are unique per-site, but are they per-account? edit: The spec[1] is vague on this, but it looked like a Relying Party can't correlate accounts directly via some kind of identifier for the authenticator. It looks like individual key pairs are genera…

You have to distinguish between resident keys and non-resident keys (that I'll just call "normal keys"). Resident keys are stored on the device, so today you can only have a limited number of RKs. This said it's a temp limitation. As usage will increase, devices will allow for more RKs. For example, if I'm not wrong, yubikeys support 25 RKs, solokeys 50. (But the only sites where you can use RKs are basically Microso…

> When you enroll a device in, say, your primary Google account, trying to enroll the same device again produces the same cryptographic key.

That's not correct. The keys are random so of course there would be statistically no chance to get the same one.

However, if you actually try to do this it simply doesn't work, it says you already enrolled this authenticator, which is true. How does it know? During enrollment the site presents a list of identifiers it already knows for your account, and your browser shows this list to all your authenticators, they won't re-enroll if they recognise an identifier as their own.

This delivers a nice UX. If you have several authenticators you don't need to unplug ones that were already enrolled to enroll more. Likewise you don't need to unplug the ones that don't know, say, Facebook credentials, to log into Facebook, the browser will see OK, this authenticator can't help me, let's try the others.

If you own the backend (I have a test system for this) you can just not provide that list of existing identifiers and if you do that the authenticator will cheerfully generate a fresh key pair (different from the first one) and complete enrolment again for the new key pair. A real site should never do that.

Re: Getting a biometric security key right

#40

Post by NiceWayToDoIT »

Does it worth repeating that "fingerprints are usernames, not passwords"?

It is straightforward to copy someone's fingerprint. If technology does not include some additional biometric property (blood vessel arrangement, unique capacitance?!, unique heat signature that will not change over time?! ...) that is hard to obtain, it is pretty much useless, especially if someone is really keen to hack you ...

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