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0 pointsabhv8mo ago0 comments

(1) in this case, an identity issuer provides the source of truth identity information. Examples include state DMV, your passport (you can try "Id pass" in Google wallet), etc.

(2) One of the goals of this project was to layer ZK on top of current identity standards that DMVs already issue, so that gov orgs don't have to change what they currently do to support the strongest user privacy. One example format is called Mdoc.

(3) The user holds the identity information on their device only. No other copies. The user's device makes the zkp proof on-device. This was one of the major technical challenges.

(4) The relying party (eg a website) runs the zk verification algorithm on the proof that is produced by the device to ensure soundness.

(5) Yes, the user can use any compatible implementation to produce the proof. We have open-sourced our implementation and we have a spec for the proof format that others can also reimplement.

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miki1232118mo ago

If you can achieve RCE on the chip and run arbitrary code without invalidating signatures, does the protocol still stay secure?

If so, what's the point of requiring your implementation to run on a verified secure element? If not, the protocol seems only as strong as the weakest chip, as obtaining just a single private key from a single chip would let you generate arbitrary proofs.

MatteoFrigo8mo ago

The role of the secure element is only to "bind" the credential to the device, so that if you copy the credential somewhere else then the credential is useless. Concretely, the secure element produces a ECDSA signature that must be presented together with the credential. This is the normal protocol without ZKP. Concretely, the SE is in the phone, but could be a yubikey or something else.

The ZKP library does not run on the secure element. It runs on the normal CPU and produces a proof that the ECDSA signature from the SE is valid (and that the ECDSA signature from the issuer is valid, and that the credential has not expired, and ...) If you crack the ZKP library, all you are doing is producing an incorrect proof that will not verify.

tzs8mo ago

Am I correctly understanding that I'd get the credential from say my state DMV once, and then later whenever I want to prove my age to a website the proof protocol is just between that website and my device? The DMV gets no information about what websites I use the DMV credential with and they get no information about when I use the credential even if the website and the DMV decide to cooperate? All they would be able to get was that at time T someone used a credential on the site that came from the DMV?

I tried to sketch out a design an age verification system, but it involved the DMV in each verification, which made timing attacks a problem. Briefly the website would issue a token, you'd get a blind signature of the token from the DMV's "this person is 18+" service, and return the token and unblinded signature to the website. I think that can be made to work but if the site and DMV cooperated they would likely be able to unmask many anonymous site users by comparing timing.

Getting the DMV out of the picture once your device is set up with the credential from them nicely eliminates that problem.

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nixpulvis8mo ago

Would something like this be considered a ZK proof? https://crypto.stackexchange.com/questions/96232/zkp-prove-t...

MatteoFrigo8mo ago

No. ZK has a technical definition I don't want to get into, but note that the described system is deterministic and it always produces the same proof for Alice on a given day, and the proof for a later day can be derived from the proof for an earlier day. So two proofs can be linked back to Alice, and thus the system is not ZK. You need some kind of randomness for ZK.

nixpulvis8mo ago

Makes sense.

coldpie8mo ago

Thanks for the reply. So in theory, I could get this MDOC file and store it on my desktop computer, and use an open-source library whose behavior I can verify, to provide the proof to the website via my web browser. Yeah? This sounds good to me.

MatteoFrigo8mo ago

No. Using the MDOC requires a signature from a hardware security key in the phone, and a lot of the complexity is how to avoid leaking the private key, which would identify you.

coldpie8mo ago

Well, that's not great. My phone is closed-source and its software is provided by an ad company. I do not trust it to always behave in my interests.

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doctorpangloss8mo ago

Are you trying to say that there’s a signed blob called an MDOC, that happens to have the age and name of the user, and this library allows a website to prove that the provided age belongs to the person with the MDOC, but not also see the name?

JoshMandel8mo ago

But to be clear, mdoc already accounts for this through its selective disclosure protocol, without the need for a zero knowledge proof technology. When you share an mdoc you are really just sharing a signed pile of hashes ("mobile security object") and then you can choose which salted pre-images to share along with the pile of hashes. So for example your name and your birth date are two separate data elements and sharing your MSO will share the hashes for both, but you might only choose to share the pre-image representing your birthday, or even a simple boolean claim that you are over 21 years old.

What you don't get with this scheme (and which zero knowledge proofs can provide) is protection against correlation: if you sign into the same site twice or sign into different sites, can the site owners recognize that it is the same user? With the design of the core mdoc selector disclosure protocol, the answer is yes.

MatteoFrigo8mo ago

Yes

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miki1232118mo ago

If you can achieve RCE on the chip and run arbitrary code without invalidating signatures, does the protocol still stay secure?

MatteoFrigo8mo ago

tzs8mo ago

Getting the DMV out of the picture once your device is set up with the credential from them nicely eliminates that problem.

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nixpulvis8mo ago

Would something like this be considered a ZK proof? https://crypto.stackexchange.com/questions/96232/zkp-prove-t...

MatteoFrigo8mo ago

nixpulvis8mo ago

Makes sense.

coldpie8mo ago

MatteoFrigo8mo ago

No. Using the MDOC requires a signature from a hardware security key in the phone, and a lot of the complexity is how to avoid leaking the private key, which would identify you.

coldpie8mo ago

Well, that's not great. My phone is closed-source and its software is provided by an ad company. I do not trust it to always behave in my interests.

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doctorpangloss8mo ago

JoshMandel8mo ago

MatteoFrigo8mo ago

Yes

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