W3C home > Mailing lists > Public > public-credentials@w3.org > June 2016

Re: Proof of possession

From: Manu Sporny <msporny@digitalbazaar.com>
Date: Tue, 14 Jun 2016 09:50:00 -0400
Message-ID: <57600B88.3030207@digitalbazaar.com>
To: public-credentials@w3.org
On 06/14/2016 03:13 AM, David Chadwick wrote:
> Having read the latest architecture document
> 
> http://w3c.github.io/webpayments-ig/VCTF/architecture/v4/
> 
> I note that there is no explicit mention of proof of possession
> (PoP).

PoP is an implementation detail based on the "Subject Identifier" and
the contents of the "Digital Signature of Issuer":

http://w3c.github.io/webpayments-ig/VCTF/architecture/v4/#verifiable-claim

We have tried very hard to not inject implementation details into the
architecture diagram. Implementation details are what the Verifiable
Claims Working Group are supposed to determine.

> Is this because the group has not discussed this topic, or has
> already decided to recommend or prohibit the use of
> 
> bearer tokens, public keys of subjects, or subject identifiers

None of those have been "prohibited from use" in phase I of the
Verifiable Claims Working Group charter work. Phase I is about
establishing a data model and set of syntaxes for expressing verifiable
claims.

One deployment may choose bearer tokens (for the purposes of
implementation ease or pseudo-anonymity), another may use public keys of
subjects (if Subject and Holder are the same), another may use public
keys of holders (if Subject and Holder are different).

> I tend to get the impression that subject identifiers seem to be the 
> implicit way of providing PoP. Is this correct?

Yes, more or less. This is what an entry in the Identifier Registry
looks like today:

https://authorization.io/dids/did:76d0cdb7-9c75-4be5-8e5a-e2d7a35ce907

"id" is the Subject Identifier
"publicKey" is the Subject Identifier's public key

One way the registry could be implemented in the long term is storing
this information in a Kademlia+ hardened DHT with a
Blockchain/Generalized Ledger storing the history for each Subject
Identifier. Note that I said ONE way that it could be implemented, there
are many - each with their benefits and drawbacks.

Also note that this is an implementation detail and we don't need to
solve this problem for the Phase I work. It's discussed in the
architecture so that folks have a better idea of the type of system that
we're trying to build.

-- manu

-- 
Manu Sporny (skype: msporny, twitter: manusporny, G+: +Manu Sporny)
Founder/CEO - Digital Bazaar, Inc.
blog: The Web Browser API Incubation Anti-Pattern
http://manu.sporny.org/2016/browser-api-incubation-antipattern/
Received on Tuesday, 14 June 2016 13:50:28 UTC

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