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Comment by perching_aix | Hacker News Reader

Wouldn't those "documents" need to be code for that to happen?

Let's say the usecase is to prove that you're 21+ to enter a bar in the US. I don't want to have to hand over my ID with my personal information on it.

On my phone, I could have the "proof", which can be validated by the door guard with a simple NFC device (ie: another phone) that is compatible with that proof.

I really doubt any cryptographic primitive can solve this; what's stopping me from lending my "proof" to my little brother?

If you have digital id signed with government keys (like passport) you would prove that person has ID where the age is above 18, attached to this photo and that all the info comes from a single government sanctioned id.

You don’t need to conceal all the data. Just the bits you don’t want to leak.

If you're going with a "digital id signed with government keys", then we don't need a ZKP, we can just use digital signatures. A certificate from the government that says "the holder of this id is 18+" is all the information that needs to be contained in the certificate.

That is a moving target. I could be 17 today and 18 tomorrow. Also it is not feasable to make all the different variations of ID but they do give out single one with all the info.

[1]https://ethresear.ch/t/zero-knowledge-proofs-of-identity-usi...

Part of the problem is that "normal" digital signatures create correlation factors that can be used to track/profile users, whereas a zero knowledge proof (over knowledge of a valid signature) could prevent this.

The app shows your face on it and says it is 21+.

How is this different from showing a non-digital driver's license that says you're 21+? Underage kids borrow each others' driver's licenses, so they can borrow each others' phones.

I'm failing to parse your argument here. We're talking about an example usecase of zkProofs as a way to better explain the technology. We're not trying to solve the problem with every different random way to sneak into a club that you can think of.

I actually was a club owner in San Francisco at one point in time. Even went through the ABC training. Got sued at one point by the ABC cause they snuck someone in under age. No system is perfect.

But, I'll tell you that having someone show me a cell phone with my picture on it, nicely large and backlit and saying I'm 21, is a great solution to requiring people to present an ID that could come from one of 1000 places.

> But, I'll tell you that having someone show me a cell phone with my picture on it, nicely large and backlit and saying I'm 21, is a great solution to requiring people to present an ID that could come from one of 1000 places.

I agree, but I already have a California DMV app that does this. It doesn't need a ZKP.

> I'm failing to parse your argument here. We're talking about an example usecase of zkProofs as a way to better explain the technology.

Indeed my argument is that ZKP seems unnecessary in this example, and yes it's extremely hard for me to appreciate the usefulness of a ZKP with an example where it seems useless.

> I agree, but I already have a California DMV app that does this. It doesn't need a ZKP.

What happens when you aren't in California? Or what happens when someone from outside of California comes to a bar.

> Indeed my argument is that ZKP seems unnecessary in this example, and yes it's extremely hard for me to appreciate the usefulness of a ZKP with an example where it seems useless.

Then go find better examples if you're this interested.

The door guard needs to validate your face matches your ID. In you example you provide the door guard with proof that you are in real-time communication with a real ID, not that it's yours.

A challenge response would be the door guard provides you with a picture of yourself, and then you run their verification code with the picture and your ID.

However, you would also want to take into account multi-venue barring lists, which would require you to provide that you're not on a list of people (that you don't have access to).

In reality, this gets complicated very fast, and I would much prefer to just show the door guard my ID rather than involve computers in any way shape or form, let alone ZK systems.

The app shows your face on it and says it is 21+.

That isn't a challenge/response flow, that's the app on your device asserting something in isolation.

The challenge is from the security guard who won't let you into the club without proof that you're 21+.

Those documents would need to be cryptographically signed machine readable data, json, a pdf (difficult).

Getting governments, banks, and other trusted third parties to sign documents is very difficult, but is happening in some cases.

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