Re: [Cfrg] ZKP for proving ownership of a credential

[Tony Arcieri <[e-mail]>]

On Tue, Jun 2, 2015 at 7:18 PM, Manu Sporny <[e-mail]>
wrote:

> We have a subset of credentials, like proof of citizenship ("this person
> is a citizen of the United Kingdom") and proof of age ("this person is
> above the age of 21"), that we believe could be asserted without leaking
> information that could be used by colluding websites* to identify the
> individual with the credential.


Do you have more specific requirements than that? I know those are just
some contrived examples, but if those are really your only requirements,
the simple administrative solution in my mind is to simply only issue these
types of credentials to people who meet these criteria in the first place.
If you can solve the problem that way, I think you can use a simpler scheme
than a zero knowledge proof. I say this specifically because I don't think
getting any more fine-grained than citizenship and age is important to
solve this particular problem, and if that's the case, there are simpler
privacy-preserving systems that are easier to implement and reason about.

Here's a scheme I think fits into this general problem space and doesn't
require a zero knowledge proof. I should probably mention one of the chairs
name is on the paper:

https://eprint.iacr.org/2006/080.pdf

I'm not sure this is particularly well suited to your proposed problem, but
I'm wondering if your proposed problem could be simplified in such a way
that it would fit.

-- 
Tony Arcieri