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Re: Identifiers in Verifiable Credentials

From: Steve Capell <steve.capell@gmail.com>
Date: Tue, 8 Jun 2021 08:41:08 +1000
Message-Id: <9E336E58-C939-4207-AD81-F64E3EBDEA09@gmail.com>
Cc: public-credentials@w3.org
To: David Chadwick <d.w.chadwick@verifiablecredentials.info>
You are welcome ;)

But I did read it carefully (pasted text below) and I still disagree.  The reason goes back to the same discussion I constantly seem have on this thread.  That the group thinks almost exclusively about VCs about people.  Whilst I think almost exclusively about VCs about things - and occasionally about businesses. 

Permits, licences, certificates issued about businesses or consignments  - almost always can (and must) be revocable - in a business sense, not just a technical / PKI sense.  Leaving that to the vagaries of different semantics seems to impose a big interoperability risk.  

Then again, I suppose there’s nothing to stop an issuer revoking a credential using the “technical protocol” even if the cause is that a non compliance demands that the export permit be revoked….?

Your text :

“ There are two aspects of revocation that are potentially of concern to VC stakeholders, in particular, to verifiers. The first is that which is typically referred to as revocation in the PKI world, and this means that the VC should not be trusted because either the cryptography is broken, or the private key of the issuer or subject has been stolen etc. In this first case, the underlying identity information is still valid e.g. the subject is still a citizen of the country, is still a member of the club etc. but the VC cannot be relied upon to verify this. For example, a thief might be able to use a cryptographically broken VC to masquerade as the subject, hence it needs to be revoked. The second aspect is that the underlying assertion is no longer valid e.g. the subject is dead or is no longer a member of the club etc. Since the VC working group is not interpreting the semantics of the VC attributes, then this latter aspect is out of scope of the working group (in just the same way that negative VCs are out of scope). Consequently we will only concentrate on revoking VCs as part of their life cycle, when the cryptography cannot be relied upon to verify the VC.”

Steven Capell
Mob: 0410 437854

> On 8 Jun 2021, at 12:48 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> 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> 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> 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> 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
>>>>>>>>> 
>>>>>>>>> 

Received on Monday, 7 June 2021 22:42:11 UTC

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