W3C home > Mailing lists > Public > public-credentials@w3.org > June 2021

Re: Identifiers in Verifiable Credentials

From: Brent Zundel <brent.zundel@evernym.com>
Date: Mon, 7 Jun 2021 09:06:47 -0600
Message-ID: <CAHR74YWbDoJ6WdduQEfq=V9UbOcPNmJRNtnDp71A51GXgaSubg@mail.gmail.com>
To: David Chadwick <d.w.chadwick@verifiablecredentials.info>
Cc: Steve Capell <steve.capell@gmail.com>, "W3C Credentials CG (Public List)" <public-credentials@w3.org>
One comment to support some of the things that Oliver has already
mentioned. It is not the purpose of ZKP-supportive signatures such as BBS+
to remove all points of correlation for a VC, it is to put the ability to
determine a degree of correlation as fully into the hands of the users as
possible.
While there are mechanisms that support only full disclosure, or only some
level of selective disclosure, BBS+ signatures (and others like them) can
support the entire range of possible expression, from full disclosure down
to disclosure of nothing beyond the fact that a credential of a certain
type was issued by a certain issuer.

On Mon, Jun 7, 2021 at 8:51 AM David Chadwick <
d.w.chadwick@verifiablecredentials.info> wrote:

>
> On 07/06/2021 14:02, Steve Capell wrote:
>
> Ok thanks David
>
> By the way, I found this to be very helpful
> https://w3c-ccg.github.io/vc-lifecycle/
>
> Thanks, I wrote most of this.
>
>
>
> Although I’d question the last part of section 9 where the authors assert
> (correctly) that credential semantics are out of scope but then say
> revocation is semantics so out of scope
>
> Not quite. It is saying that the second aspect is out of scope, since VCs
> say nothing about the truth of the assertions that they contain. Thus they
> cannot revoke semantically something that they dont know is true and say it
> is false.
>
>
>
> The ability to revoke a credential seems like such a ubiquitous need that
> it seems to me that it’s appropriate to put in the protocol / standard
> lifecycle layer and not leave it only in the semantic content.
>
> It supports this in the first aspect. Have a close read again
>
> Kind regards
>
> David
>
>
>
> Steven Capell
> Mob: 0410 437854
>
> On 7 Jun 2021, at 9:58 pm, David Chadwick
> <d.w.chadwick@verifiablecredentials.info>
> <d.w.chadwick@verifiablecredentials.info> wrote:
>
> 
>
> There is delegation of authority in this case. ACME delegates to its
> customer and the customer is delegating to its chosen importer. So the
> verifier is able to verify a chain of trust if this is desired. But if you
> don't want to go to this level of protection then ACME can make its VCs
> bearer credentials (so anyone who possesses them is authorised to present
> them) and the subject properties would contain a description of the subject
> object along with their properties.
>
> Kind regards
>
> David
> On 07/06/2021 11:10, Steve Capell wrote:
>
> >> ACME provides that VC
>
> The ultimate verifier is the importing customs authority. the presenter is
> the customs broker selected by the importer (who is ACMEs customer).
>
> In this scenario the subject (ACME) has no relationship with the final
> holder/presenter (customs broker) and verifier (importing authority) so
> can’t possibly provide any delegated authority.   ACME is basically saying
> (to its customer the importer), “here is proof that I’m an Australian
> trusted trader - do whatever you want with it”
>
> I suppose acme is delegating a “show this to whoever you want” authority
> to the importer
>
> Steven Capell
> Mob: 0410 437854
>
> On 7 Jun 2021, at 7:59 pm, David Chadwick
> <d.w.chadwick@verifiablecredentials.info>
> <d.w.chadwick@verifiablecredentials.info> wrote:
>
> 
>
> Hi Steve
> On 07/06/2021 10:24, Steve Capell wrote:
>
> Sorry - in the middle case I meant to say the “subject is not the
> presenter” not “the holder is not the presenter “
>
> I think the general state will be that there is a linked data graph of
> verifiable claims.  The verifier follows the thread like pulling on the end
> of a piece of string and finding forks and joins and little gems as they
> pull.
>
> Maybe there’s even a VC about a whole graph so that verifiers don’t need
> to pull the string..
>
> Steven Capell
> Mob: 0410 437854
>
> On 7 Jun 2021, at 7:15 pm, Steve Capell <steve.capell@gmail.com>
> <steve.capell@gmail.com> wrote:
>
>  What about the case where there is a subject but the VC is also
> presented by a bearer
>
> The bearer is the holder. Always.
>
>
>
> For example
>
> Issuer (border agency) issues a VC about a subject (ACME) that asserts
> that ACME is an Australian Trusted Trader.
>
> I have a similar use case to this.
>
>
>
> ACME provides that VC
>
> It is not ACME that provides it, but an authorised official of ACME that
> provides it. This official will have his/her own key pair (Unless ACME has
> its own key pair and the private key is given to authorised officials by
> some internal company procedure). Which model are you suggesting?
>
>
> (together with several others like an IP rights ownership VC (about a
> product ) and a certificate of origin VC (about a consignment) with their
> export document bundle to their customer (importer) who gives some of them
> to a customs broker who passes them to the importing border authority
> (customs) who is the verifier of the trusted trader VC and the origin VC
> (but doesn’t care about the IP rights vc). The IP rights VC is a direct
> exporter (ACME) holder to verifier (importer) VC.
>
> This is pretty much business as usual in international trade - which
> comprises maybe 10 billion consignments (and hence VC bundles) per year
>
> We have a combination of
> - pure bearer VCs (eg the origin certificate where the subject is a
> consignment of goods)
>
> A bearer VC has no subject ID. So if the subject is the goods then it is
> not a bearer VC. The VC will be held by someone other than the subject
> (unless the goods has its own digital twin which can be the holder and the
> subject).
>
>
> - traditional holder VCs (eg the trusted trader status) - except that the
> holder is not the presenter so it’s kind of a holder VC used like a bearer
> VC
>
> This is the case where the subject NE holder. In this situation the holder
> has to prove to the verifier that it is entitled to present the VC on
> behalf of the subject. There are a multitude of ways of doing this.
>
>
> - pure holder is presenter (the scenario most often discussed in this
> group but the least common in cross border trade)
>
> The holder is ALWAYS the presenter. This is the model. There are only
> subjects and holders. No other roles
>
>
>
> Whet is the correct use of subject ID and VC assertion ID in each of these
> cases?
>
> The subject ID always refers to the subject of the VC about which the
> assertions are made. What do you mean by assertion ID? VC ID?
>
> Kind regards
>
> David
>
>
>
> Steven Capell
> Mob: 0410 437854
>
> On 7 Jun 2021, at 6:52 pm, David Chadwick
> <d.w.chadwick@verifiablecredentials.info>
> <d.w.chadwick@verifiablecredentials.info> wrote:
>
> 
>
>
> On 06/06/2021 22:57, Kerri Lemoie wrote:
>
> Hello all,
>
> I have a question about identifiers in verifiable credentials. The documentation states:
>
> "When expressing statements about a specific thing, such as a person, product, or organization, it is often useful to use some kind of identifier so that others can express statements about the same thing. This specification defines the optional id property for such identifiers. The id property is intended to unambiguously refer to an object, such as a person, product, or organization. Using the id property allows for the expression of statements about specific things in the verifiable credential."
>
>
> In the credentialSubject property it seems clear that the id can represent the subject that the claim is about but I’m not clear on the uses for the optional id in the vc assertion. It would be helpful to learn about some examples or suggested uses.
>
> The id is optional for the case where the VC is a bearer VC e.g. a ticket
> to an event. This means that the properties are not bound to a subject, but
> can be presented by anyone who possesses the VC.
>
> Kind regards
>
> David
>
>
> For some context: in VC-EDU, we’re discussing Open Badges as VCs. Open Badges have historically mostly been verified via issuer hosted URLs.  One of the reasons to move away from hosted URLs is to remove the dependence on the issuer for verification. However, there may continue to be use cases for when an Open Badge should still be verified through its hosted url.
>
>
> Thanks,
>
> Kerri
>
>
>
>

-- 
Brent Zundel, Evernym
Principle Cryptography Engineer
Received on Monday, 7 June 2021 15:08:35 UTC

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