5 ms·

Excellent question. More generally, what prevents me from copying the credential and giving it to somebody else? The currently favored approach works like thi

Excellent question. More generally, what prevents me from copying the credential and giving it to somebody else? The currently favored approach works like this. The DOCUMENT contains a device public key DPK. The corresponding secret key is stored in some secure hardware on the phone, designed so that I (or malware or whatever) cannot extract the secret key from the secure hardware. Think of it as a yubikey or something, but embedded in the phone. Every presentation flow will demand that the secure element produce a signature of a random challenge from the RP under the secret key of the secure hardware. In the ZKP presentation, the ZKP prover produces a proof that this signature verifies correctly, without disclosing the secret key of the secure hardware. In your example, the parent could give the phone to the kid. However, in current incarnations, the secure hardware refuses to generate a signature unless unlocked by some kind of biometric identification, e.g. fingerprint. The fingerprint never leaves the secure hardware. How does the issuer (e.g. the republic of France) know that DOCUMENT is bound to a given fingerprint? This is still under discussion, but as a first bid, a French citizen goes to city hall with his phone and obtains DOCUMENT after producing a fingerprint on the citizen's phone (as opposed to a device belonging to the republic of France). You can imagine other mechanisms based on physical tokens (yubikeys or embedded chips in credit cards, or whatever). Other proposals involve taking pictures compared against a picture stored in DOCUMENT. As always, one needs to be clear about the threat model. In all these proposals the biometric identification unlocks the secure hardware into signing a nonce. The biometrics themselves are not part of the proof and are not sent to the relying party or to the issuer.

parineum 9mo ago
So adults are required to own a phone to prove their age? Can I log into an age gated service at a library without a phone?
- MatteoFrigo 9mo ago
  Another excellent question. The current answer in the EU seems to be "you need a phone". My preferred answer (despite being one of the Google guys who designed the ZKP mechanism) would be that the government sends you some sort of plastic card with a chip that does not tie you to a phone. Still fighting that battle.
  - parineum 9mo ago
    Thanks for answering, I appreciate it.
  - fsflover 9mo ago
    I guess owning some computer should be fine as a requirement? It just should not be tied to the US megacorps. A web app perhaps?
    - MatteoFrigo 9mo ago
      Yes. However, at some point there needs to be some unforgeable piece of hardware that prevents copying the document. I am a big fan of yubikeys and I wish everybody used them, but the reality is that people lose them way more often than they lose their phone.
donmcronald 9mo ago
> How does the issuer (e.g. the republic of France) know that DOCUMENT is bound to a given fingerprint? This is still under discussion, but as a first bid, a French citizen goes to city hall with his phone and obtains DOCUMENT after producing a fingerprint on the citizen's phone (as opposed to a device belonging to the republic of France). Are you saying that someone goes to city hall, shows ID, and gets a DOCUMENT that certifies age, but doesn't link back to the person's identity? And it's married to a fingerprint in front of the person checking ID? Is there a limit on how many times someone can get a DOCUMENT? If not, it'll become a new variation of fake id and eventually there's going to be an effort to crack down on misuse. If yes, what happens if I get unlucky and lose / break my phone limit + 1 times? Do I get locked out of the world? The only way I can imagine limiting abuse and collateral damage at the same time is to link an identity to a DOCUMENT somehow which makes the whole ZKP thing moot. I'd be more worried about the politics though. There's no way any government on the planet is going to keep a system like that limited to simple age verification. Eventually there's going to be enough pretense to expand the system and block "non-compliant" sites. Why not use the same DOCUMENT to prove age to buy beer? Sanity for guns? Loyalty for food? What happens if the proof gets flipped to run the other direction and a DOCUMENT is needed to prove you're a certified journalist? Any sources without certification can be blocked and the ZKP aspect doesn't matter at that point because getting the DOCUMENT will be risky if you're a dissenter. Maybe there's an interview. Maybe there's a background check. Has your phone ever shown up near a protest? It's just like the Android announcement that developers need to identify themselves to distribute apps, even via side loading. The ultimate goal is to force anyone publishing content to identify themselves because then it's possible to use the government and legal system to crush dissenting views. Big tech caused most of the problems and now they're going to provide the solution with more technology, more cost, and less freedom which is basically what they've been doing for the last 2 decades so it's not a surprise.
- cycomanic 9mo ago
  I somewhat understand your argument about how to prevent misuse, but I'd say one could do that by embedding the key in an ID card and someone will have to connect the ID card to the phone/computer (e.g. via NFC). So obviously you can pretend you lost your ID card and get a new one, but I would say that you can only do that so often until someone will get suspicious, just as if you would ask for a new passport every couple of months someone would start asking you some serious questions. Regarding using the document to buy beer, that's already done, you need to provide ID. I also hope you being asked to provide ID for buying guns, but then again I'm not from the US, so I have quite a different opinion on gun ownership. All that said though, we are currently watching some of the most significant civil rights abuses by authorities, all without any ID system and people are worried about age verification? If the government wants to abuse their power they don't need an ID system, they just look at your social media profile at the border.

parineum 9mo ago

So adults are required to own a phone to prove their age? Can I log into an age gated service at a library without a phone?

MatteoFrigo 9mo ago
Another excellent question. The current answer in the EU seems to be "you need a phone". My preferred answer (despite being one of the Google guys who designed the ZKP mechanism) would be that the government sends you some sort of plastic card with a chip that does not tie you to a phone. Still fighting that battle.
- parineum 9mo ago
  Thanks for answering, I appreciate it.
- fsflover 9mo ago
  I guess owning some computer should be fine as a requirement? It just should not be tied to the US megacorps. A web app perhaps?
  - MatteoFrigo 9mo ago
    Yes. However, at some point there needs to be some unforgeable piece of hardware that prevents copying the document. I am a big fan of yubikeys and I wish everybody used them, but the reality is that people lose them way more often than they lose their phone.

donmcronald 9mo ago

> How does the issuer (e.g. the republic of France) know that DOCUMENT is bound to a given fingerprint? This is still under discussion, but as a first bid, a French citizen goes to city hall with his phone and obtains DOCUMENT after producing a fingerprint on the citizen's phone (as opposed to a device belonging to the republic of France). Are you saying that someone goes to city hall, shows ID, and gets a DOCUMENT that certifies age, but doesn't link back to the person's identity? And it's married to a fingerprint in front of the person checking ID? Is there a limit on how many times someone can get a DOCUMENT? If not, it'll become a new variation of fake id and eventually there's going to be an effort to crack down on misuse. If yes, what happens if I get unlucky and lose / break my phone limit + 1 times? Do I get locked out of the world? The only way I can imagine limiting abuse and collateral damage at the same time is to link an identity to a DOCUMENT somehow which makes the whole ZKP thing moot. I'd be more worried about the politics though. There's no way any government on the planet is going to keep a system like that limited to simple age verification. Eventually there's going to be enough pretense to expand the system and block "non-compliant" sites. Why not use the same DOCUMENT to prove age to buy beer? Sanity for guns? Loyalty for food? What happens if the proof gets flipped to run the other direction and a DOCUMENT is needed to prove you're a certified journalist? Any sources without certification can be blocked and the ZKP aspect doesn't matter at that point because getting the DOCUMENT will be risky if you're a dissenter. Maybe there's an interview. Maybe there's a background check. Has your phone ever shown up near a protest? It's just like the Android announcement that developers need to identify themselves to distribute apps, even via side loading. The ultimate goal is to force anyone publishing content to identify themselves because then it's possible to use the government and legal system to crush dissenting views. Big tech caused most of the problems and now they're going to provide the solution with more technology, more cost, and less freedom which is basically what they've been doing for the last 2 decades so it's not a surprise.

cycomanic 9mo ago
I somewhat understand your argument about how to prevent misuse, but I'd say one could do that by embedding the key in an ID card and someone will have to connect the ID card to the phone/computer (e.g. via NFC). So obviously you can pretend you lost your ID card and get a new one, but I would say that you can only do that so often until someone will get suspicious, just as if you would ask for a new passport every couple of months someone would start asking you some serious questions. Regarding using the document to buy beer, that's already done, you need to provide ID. I also hope you being asked to provide ID for buying guns, but then again I'm not from the US, so I have quite a different opinion on gun ownership. All that said though, we are currently watching some of the most significant civil rights abuses by authorities, all without any ID system and people are worried about age verification? If the government wants to abuse their power they don't need an ID system, they just look at your social media profile at the border.