Re: When to use pair-wise unique DIDs vs. just individual unique DIDs

On Sat, Apr 14, 2018 at 9:46 AM, Chris Boscolo <chris@boscolo.net> wrote:

> First, Adam, thanks for posting the "WebAuthn & DID" presentation that
> surfaced the discussion of using pair-wise unique DIDs.  And thank
> you, Drummond, for linking to the discussion taking place at Sovrin on the
> subject. (https://forum.sovrin.org/t/the-benefit-of-pairwise-dids/628/3)
>
> I decided to pull this one question out into its own thread to get
> clarification and to help inform how the WebAuthn protocol might be
> modified to support DIDs.
>
> I think the community would benefit if we had a clear understanding of
> when pair-wise unique DIDs should be used vs. when a per-user unique DIDs
> will suffice.
>
> In the example, where a user is creating a new account on a popular
> website it is clear to me that the user will want to use a unique DID for
> only that site.  But, I question whether it is a good idea for the website
> to create a unique DID to communicate with that one user.  In fact, I
> wonder if doing so will open the door to other unintended ways of
> correlating users with the site. (When these DIDs are in public ledgers.)
>

Chris, I just wanted to point out why your final parenthetical is important
to this discussion. In Sovrin architecture, pairwise pseudonymous DIDs *are
not written to the public ledger*.

It's true that a year ago, even as we started to use pairwise pseudonymous
DIDs, we assumed they were all being written to the Sovrin public ledger
because: a) they did not provide any correlate-able data, and b) we didn't
have an alternative.

We subsequently realized that, since the whole point of pairwise
pseudonymous DIDs is that they are only needed by the two parties
involved—and that each can maintain a copy of the other's DID
document—there was no reason to write them to a public ledger. Rather the
two parties could maintain them on their own private microledger.

This has several significant advantages:

   1. It is even better from a privacy perspective since neither the
   pairwise pseudonymous DIDs nor their DID documents needed to be public.
   2. It is wonderful from a scalability perspective since the microledgers
   add almost no load to the public ledger.
   3. It means the Sovrin public ledger can be optimized for public DIDs
   and other SSI infrastructure data that needs to be fully public and widely
   shared.

Should these considerations be added to the DID spec?
>

That's a very good question. I don't think the DID spec (or any other spec)
should be weighed down with lots of implementation guidelines and advice,
but we should probably mention the basic option that DIDs can be registered
on public ledgers, private ledgers, or microledgers.

What do you think?