Hashed claim values #47

David-Chadwick · 2019-08-22T10:41:03Z

fixes #42

hashed claim values

TallTed · 2019-08-22T14:42:55Z

index.html

@@ -1642,6 +1642,18 @@ <h3>Selective Disclosure</h3>
 all of the credential's claims to be revealed.

          </li>
+          <li>
+<b> Hashed Values</b> - With this method, the <a>issuer</a> issue a single


 Hashed Values - With this method, the <a>issuer</a> issue a single
-> Hashed Values — With this method, the <a>issuer</a> issues a single

 Hashed
-> Hashed
was overlooked

TallTed · 2019-08-22T14:44:26Z

index.html

@@ -1642,6 +1642,18 @@ <h3>Selective Disclosure</h3>
 all of the credential's claims to be revealed.

          </li>
+          <li>
+<b> Hashed Values</b> - With this method, the <a>issuer</a> issue a single
+<a>verifiable credential</a> containing all the subject's <a>claims</a>.


all the subject's <a>claims</a>.
-> all the <a>issuer</a>'s <a>claims</a> about the <a>subject</a>.

TallTed · 2019-08-22T14:54:35Z

index.html

+<code>credentialSubject</code> contains the identifier of the hashing
+algorithm used to create all the hashed values. The holder includes the actual
+values of the <a>claims</a> that are to be revealed to the <a>verifier</a> in
+the <a>verifiable presentation</a>.


More rewording is needed. Perhaps replacing your "actual value" with "original
literal value" would work... as --

However, each <a>claim</a> value in the <a>verifiable credential</a> is created by hashing the original literal value with a different nonce. The value for the <a>claim</a> in the <a>verifiable credential</a> then comprises an object containing 1) the nonce and 2) the hashed value of the nonce concatenated with the original literal <a>claim</a> value. In addition, the <code>credentialSubject</code> contains the identifier of the hashing algorithm used to create all the hashed values. The holder includes the original literal values of the <a>claims</a> they intend to reveal to the <a>verifier</a> in their <a>verifiable presentation</a>.

I am a bit confused by the <code>credentialSubject</code> contains the identifier of the hashing algorithm. Does the <code>credentialSubject</code> here not contain the identifier of the subject of the credential? Or does it include both identifiers (making it an array, rather than a single value)? Or something else?

I think that 'actual value' is better than 'original literal value'

The credentialSubject comprises a whole set of attributes, including the id. This is a proposal to add another property to this set i.e. the hashing algorithm. I will clarify this.

Having a hashing algorithm as a property of a credentialSubject makes very little sense. It would mean, for example, that a VC about David Chadwick would state that David has a hashing algorithm of SHA-256.

It sounds like this information should be captured in the proof section somewhere instead.

The hashing algorithm is actually a property of the claim value e.g. the claim {name=David} is transposed into {name={hashID=SHA-256, nonce=123....9, value=a8clyga}}. But since the same hashing algorithm is used for all claim values, there is no point in repeating the hashing algorithm ID multiple times. So we move it up a level to the encapsulating object, which is the credentialSubject, and put it there.

Has this been resolved? I lean towards what @dlongley said above. The hashing algorithm, and all cryptographic attributes should be decoupled from the contents of the credentialSubject.

If we had a data model in which a credentialSubject contained an ID and a set of claims, and each claim contained an ID and a set of properties, then we could have explicitly placed the hashID in the claim object. But unfortunately the data model has not explicitly identified the claim object with a claim ID and so the fact that this exists is obscured (and has led to many previous misunderstandings and issues.) Thus you think (wrongly) that the hashID is a property of the credentialSubject, when in fact, it is a property of the (invisible) claim object.

@David-Chadwick, btw, (we don't need to mention this), but there has been other exploratory work in this area that involves reducing nonce storage via HMAC keys and that transforms the data to RDF quads prior to hashing -- and other work that uses URLs to store the hash values.

I think given that there are a number of ways to do the above scheme that we should perhaps just leave a note saying that it is up to the proof scheme to figure out how it's done -- like we do with ZKPs. We won't need to debate this further if we take that approach. It's worth just noting the nonce+hash method here as a means of redaction. We can also point to the CCG for further work in the area.

TallTed · 2019-08-22T14:56:37Z

fixes #42

(@David-Chadwick -- note that the line above, including the space before the #, associates this PR with that Issue, and if you include it in your initial post (and possibly in one of your comments), merging this PR will then auto-close that issue.)

David-Chadwick · 2019-08-22T19:14:13Z

fixes #42

TallTed · 2019-08-22T19:33:34Z

@David-Chadwick - I was wrong about putting it in a comment. If you edit your initial post/comment on this PR, and add fixes #42, you should then (after saving your edit) see that fixes is highlighted, and if you mouse over it, you'll see a tooltip from GitHub -- like what you can see here.

deiu · 2019-08-27T07:27:15Z

The issue autofix text can also be added during merge, don't worry too much about it.

dlongley

Left some spelling, etc. nits.

dlongley · 2019-08-27T15:14:19Z

index.html

@@ -1642,6 +1642,17 @@ <h3>Selective Disclosure</h3>
 all of the credential's claims to be revealed.

          </li>
+          <li>
+<b> Hashed Values</b> &mdash; With this method, the <a>issuer</a> issues a single


Suggested change

 Hashed Values — With this method, the <a>issuer</a> issues a single

Hashed Values - With this method, the <a>issuer</a> issues a single

@dlongley My original text had it your way, but @TallTed said I should change it to the current way. So can I suggest that the two of you agree between yourselves which way you want it to be. Thanks.

After reviewing the existing text I see that the two previous bullets already use -, so I have changed mine back to this (how it was originally).

dlongley · 2019-08-27T15:14:48Z

index.html

+about the subject.
+However, each <a>claim</a> value is created by hashing the actual value with
+a different nonce so that the <a>verifier</a> cannot determine the actual value.
+There are several different ways of modelling this, and


Suggested change

There are several different ways of modelling this, and

There are several different ways of modeling this, and

TallTed · 2019-08-27T20:55:36Z

index.html

-hashed values. The holder includes the actual
+a different nonce so that the <a>verifier</a> cannot determine the actual value.
+There are several different ways of modelling this, and
+no standard way is currently defined. The holder includes the actual


holder
->
<a>holder</a>

Update index.html

243023d

hashed claim values

TallTed reviewed Aug 22, 2019

View reviewed changes

TallTed mentioned this pull request Aug 22, 2019

Selective Disclosure #42

Closed

Update index.html

249b281

Update index.html

c491b00

dlongley approved these changes Aug 27, 2019

View reviewed changes

Update index.html

ab67ef2

TallTed reviewed Aug 27, 2019

View reviewed changes

David-Chadwick added 2 commits August 28, 2019 07:35

Update index.html

1385a14

Update index.html

288a262

deiu added the Ready for merge label Aug 28, 2019

deiu merged commit bf183a5 into gh-pages Aug 28, 2019

deiu deleted the Selective-Disclosure branch August 28, 2019 08:00

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Hashed claim values #47

Hashed claim values #47

David-Chadwick commented Aug 22, 2019 •

edited by pr-preview bot

TallTed Aug 22, 2019

David-Chadwick Aug 22, 2019

TallTed Aug 22, 2019

TallTed Aug 22, 2019

David-Chadwick Aug 22, 2019

TallTed Aug 22, 2019

David-Chadwick Aug 22, 2019

dlongley Aug 22, 2019

David-Chadwick Aug 23, 2019

deiu Aug 27, 2019

David-Chadwick Aug 27, 2019

dlongley Aug 27, 2019

TallTed commented Aug 22, 2019 •

edited

David-Chadwick commented Aug 22, 2019

TallTed commented Aug 22, 2019 •

edited

deiu commented Aug 27, 2019

dlongley left a comment

dlongley Aug 27, 2019

David-Chadwick Aug 28, 2019

David-Chadwick Aug 28, 2019

dlongley Aug 27, 2019

David-Chadwick Aug 28, 2019

TallTed Aug 27, 2019

David-Chadwick Aug 28, 2019

	<b> Hashed Values</b> — With this method, the <a>issuer</a> issues a single
	<b>Hashed Values</b> - With this method, the <a>issuer</a> issues a single

	There are several different ways of modelling this, and
	There are several different ways of modeling this, and

Hashed claim values #47

Hashed claim values #47

Conversation

David-Chadwick commented Aug 22, 2019 • edited by pr-preview bot

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

TallTed commented Aug 22, 2019 • edited

David-Chadwick commented Aug 22, 2019

TallTed commented Aug 22, 2019 • edited

deiu commented Aug 27, 2019

dlongley left a comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

David-Chadwick commented Aug 22, 2019 •

edited by pr-preview bot

TallTed commented Aug 22, 2019 •

edited

TallTed commented Aug 22, 2019 •

edited