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Add interoperable way for holder-asserted claims in a VP #1186

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Add interoperable way for holder-asserted claims in a VP #1186

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7490cfb
add section on holder-derived creds in VP
brentzundel Jul 5, 2023
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soften requirement for 'type', clarify two methods for VC.
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add paragraph clarifying subjects of self-asserted VCs
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bef11ba
re-phrase normative considerations, add example
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Merge branch 'issue-860' of github.com:brentzundel/vc-data-model into…
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Update title for holder-asserted example.
msporny Jul 14, 2023
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remove controversial recommended 'type'
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change example title
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modify example 2 with Joe's language
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Expand Up @@ -2030,6 +2030,111 @@ <h4>Presentations Using Derived Credentials</h4>
</figcaption>
</figure>
</section>
<section>
<h4>Presentations Including Holder Claims</h4>
<p>
A <a>holder</a> MAY use the <code>verifiableCredential</code> <a>property</a> in
a <a>verifiable presentation</a> to include <a>verifiable credentials</a> from
any <a>issuer</a>, including themselves. When the <a>issuer</a> of a
<a>verifiable credential</a> is the <a>holder</a>, the <a>claims</a> in that
<a>verifiable credential</a> are considered to be <em>self-asserted</em>.
Such self-asserted claims can be secured by the same mechanism that secures
the <a>verifiable presentation</a> in which they are included or by any
mechanism usable for other <a>verifiable credentials</a>.
</p>
<p>
The <a>subject(s)</a> of these self-asserted <a>claims</a> are not limited, so
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these <a>claims</a> can include statements about the <a>holder</a>, one of the
other included <a>verifiable credentials</a>, or even the <a>verifiable
presentation</a> in which the self-asserted <a>verifiable credential</a> is
included. In each of these cases, the <code>CredentialSubject</code> would
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included. In each of these cases, the <code>CredentialSubject</code> would
included. In each of these cases, the <code>credentialSubject</code> value would

have an <code>id</code> <a>property</a> that matches the <code>id</code> of
the <a>subject</a>, just as it is done in <a>verifiable credentials</a> that
are not self-asserted.
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</p>
<p>
A <a>verifiable presentation</a> that includes a self-asserted
<a>verifiable credential</a> that is only secured using the same mechanism as
the <a>verifiable presentation</a> MUST include a <code>holder</code>
<a>property</a>.
</p>
<p>
All of the normative requirements defined for <a>verifiable credentials</a>
apply to self-asserted <a>verifiable credentials</a>. Some additional
considerations follow:
</p>

<dl>
<dt><var>type</var></dt>
<dd>
It is RECOMMENDED that <code>SelfAssertedCredential</code> be included as an
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I agree with @selfissued and @dlongley that this is not necessary. You can just check to see if the key used to sign a VC belongs to the holder. For Data Integrity, you check to see if the proof.verificationMethod is associated with holder using the algorithm defined in https://w3c.github.io/vc-data-integrity/#retrieve-verification-method. I expect VC COSE JOSE would define the same sort of mapping. IOW, just because someone asserts this, doesn't mean it's true, you need to verify it... and if only a subset of the ecosystem is doing it, you can't really count on it as a dependable mechansim.

This feedback is non-blocking, just thinking out loud.

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I expect VC COSE JOSE would define the same sort of mapping. IOW, just because someone asserts this, doesn't mean it's true, you need to verify it... and if only a subset of the ecosystem is doing it, you can't really count on it as a dependable mechanism.

This describes "Verifiable Presentations" as a whole... And I agree... its not very helpful.

We seem to have to do a lot of work for "holder" and "VerifiablePresentation"... when they are really just special cases of "issuer" and "VerifiableCredential"....

I continue to assert there is a better solution to this, but I don't think we can turn this boat at this point.

additional <code>type</code> value. For example,<br>
<code>"type": ["VerifiableCredential", "SelfAssertedCredential", "ExampleTypeCredential"]</code>
</dd>
<dt><var>issuer</var></dt>
<dd>
For self-asserted <a>verifiable credentials</a> that are secured using the same
mechanism as the <a>verifiable presentation</a>, the value of the
<code>issuer</code> <a>property</a> MUST be identical to the <code>holder</code>
<a>property</a> of the <a>verifiable presentation</a>.
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</dd>
</dl>
<p>
The example below shows a <a>verifiable presentation</a> that embeds a
self-asserted <a>verifiable credential</a> that is secured using the same
mechanism as the <a>verifiable presentation</a>.
</p>

<pre class="example nohighlight" title="A secured verifiable presentation relying on an embedded proof, including a self-asserted verifiable credential">
{
"@context": [
"https://www.w3.org/ns/credentials/v2",
"https://www.w3.org/ns/credentials/examples/v2"
],
"type": ["VerifiablePresentation", "ExamplePresentation"],
"holder": "did:example:12345678",
"verifiableCredential": [{
"@context": "https://www.w3.org/ns/credentials/v2",
"type": ["VerifiableCredential", "SelfAssertedCredential", "ExampleFoodPreferenceCredential"],
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"issuer": "did:example:12345678",
"credentialSubject": {
"favoriteCheese": "Gouda"
},
{ <span class="comment">...</span> }
}],
"proof": [{ <span class="comment">...</span> }]</span>
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}
</pre>
<p>
The example below shows a <a>verifiable presentation</a> that embeds a
self-asserted <a>verifiable credential</a> that holds <a>claims</a> about the
<a>verifiable presentation</a>. It is secured using the same mechanism as the
<a>verifiable presentation</a>.
</p>

<pre class="example nohighlight" title="Verifiable presentation with a self-asserted verifiable credential about the verifiable presentation">
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@OR13 OR13 Jul 14, 2023 •
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<pre class="example nohighlight" title="Verifiable presentation with a self-asserted verifiable credential about the verifiable presentation">
<pre class="example nohighlight" title="A secured verifiable presentation, relying on an embedded proof, including a self-asserted verifiable credential about the verifiable presentation">

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for consistency with https://github.com/w3c/vc-data-model/pull/1186/files#r1264100438

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@msporny as an aside, I suspect your PR to fix credential vs verifiable credential will be some version of these changes... over and over again... until you go mad.... : )

Basically replacing credential with unsecured verifiable credential or secured verifiable credential depending on the context... looking forward to that one : )

Maybe we can be clever and do that once in terms, and not have to be so verbose everywhere....

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@msporny msporny Jul 14, 2023 •
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until you go mad....

That happened long ago... during v1.0... :)

I'll see if we can be clever wrt. terminology, as you mention above... but at this point, I'm leaning toward NOT making the change (as it sounds like it's going to be a lot of trouble, and result in a confusing outcome for readers).

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@OR13 OR13 Jul 14, 2023 •
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I don't see how we can avoid fixing it, given what it currently normatively states:

It makes the interpretation of <a>verifiable credential<a> and VerifiableCredential inconsistent.

The reader learns that embedded or external proof is required for <a>verifiable credential<a>.... and optional for VerifiableCredential... Seems like we will have to fix that... The same applies to presentations... This PR is digging the hole deeper.... but sometimes a tunnel is necessary to escape.

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changed in 8590bc1

{
"@context": [
"https://www.w3.org/ns/credentials/v2",
"https://www.w3.org/ns/credentials/examples/v2"
],
"type": ["VerifiablePresentation", "ExamplePresentation"],
<span class="highlight">"id": "http://example.com/presentation/5223"</span>,
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"holder": "did:example:12345678",
"verifiableCredential": [{
"@context": "https://www.w3.org/ns/credentials/v2",
"type": ["VerifiableCredential", "ExampleTimeLimitCredential"],
"issuer": "did:example:12345678",
"credentialSubject": {
<span class="highlight">"id": "http://example.com/presentation/5223"</span>,
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"validUntil": "2024-01-01T19:23:24Z"
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@msporny msporny Jul 17, 2023 •
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"validUntil": "2024-01-01T19:23:24Z"
"validUntil": "2024-01-01T19:23:24Z"

Huh... this is valid, and proposes the question: Why not just put validUntil on the presentation itself? We might want to have an example of someone putting a self-asserted claim on the VP itself... possibly in another PR, we don't want to complicate this one further.

IOW, do we want to enable validFrom and validUntil onto the Presentation too? I think we do want to enable that. At present, it's only allowed on a VerifiableCredential. Historically, this was because presentations were expected to always be short lived... but the short-lived-ness being determined by the verifier and the created/iat date on the proof, not explicitly stated by the holder.

This comment is non-blocking.

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@msporny I think you're probably right, but I don't want that conversation to derail this PR. I think a better example is probably be what's needed here.

This example came out of my attempt to address @jandrieu 's desire for a normative way for a holder to make claims about the VP. As I constructed the self-asserted VC, I had a hard time coming up with a claim the holder would want to make about the VP.
This is just to say that there is probably a better example of the sort of claims a holder would want to make about the VP, but I couldn't think one up. Looking to @jandrieu for suggestions.

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@msporny msporny Jul 17, 2023 •
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Agreed, we don't want to derail this PR with trying to find the perfect example. I defer to @jandrieu to suggest a use case. I'll try to think of a use case (with markup) as well (for a future PR).

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I've updated the example based on Joe's comment here: https://github.com/w3c/vc-data-model/pull/1186/files#r1268305835

},
{ <span class="comment">...</span> }
}],
"proof": [{ <span class="comment">...</span> }]</span>
}
</pre>
</section>
</section>
</section>

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