Re: [EXTERNAL] Re: [EXTERNAL] Re: Questions about ecdsa-sd-2023

Hi Manu,

On the subject of those predicates, I’ve noticed this example: https://www.w3.org/TR/vc-data-model-2.0/#fig-a-visual-example-of-the-relationship-between-credentials-and-derived-credentials-in-a-zkp-presentation transforms a VC with say `DateOfBirth` field into another derived VC with `isOver18` field in the presentation,

Is there such a solution existing at this time or is this just a wishful example?

From: Manu Sporny <msporny@digitalbazaar.com>
Date: Monday, 22 January 2024 at 16:57
To: Julien Fraichot <Julien.Fraichot@hyland.com>
Cc: W3C Credentials CG (Public List) <public-credentials@w3.org>
Subject: [EXTERNAL] Re: [EXTERNAL] Re: Questions about ecdsa-sd-2023
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On Mon, Jan 22, 2024 at 9:50 AM Julien Fraichot
<Julien.Fraichot@hyland.com> wrote:
> Thanks Manu for the detailed answer, I’ve also been having a conversation with Dave Longley on the github repo so everything is clearer now.

Good, glad it is starting to make sense.

>> Simple predicates can be done with static values. That is: "over age
>> 15", "over age 18", "over age 21".
>
> Can you elaborate on this? Is that a built-in feature of the spec/implementation – or is it by returning a piece of data such as the Date of Birth, the verifier has to implement a computational check?

Since we're talking about data structures that can be selectively
disclosed, one can imagine a verifiable credential with the following
selectively disclosable fields:

"credentialSubject": {
  ...
  "birthday": "1992-04-18",
  "ageOver15": true,
  "ageOver18": true,
  "ageOver21": true,
  "ageOver25": true,
  "ageOver65": false,
  ...
}

Using ecdsa-sd, the holder can choose to just disclose "ageOver18"
(arguably, a "predicate proof") instead of "birthday" (which would
reveal more identifying information about the subject).

-- manu

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