Re: A simpler approach to DID services and content-addressing

Manu,

Here's simpler solution using the Hyperonomy did-uri-spec specification and grammar.  See the attached "Page 47" slide where I've tried to:

  1.  capture your 3 use cases, then
  2.  create a did-uri-spec compliant an example did-uri for each use case, and finally
  3.  added a description of the output.

I've also attached a copy of the did-uri-spec grammar (defined using ABNF notation).  See attached image with a black background.

RE: "resolution algorithms"

This is a little more difficult to explain but for the most part, the "resolution algorithms" you describe are actually "parsing algorithms". When using a grammar defined using ABNF notation, the pattern matching, etc. that takes place in the automatically generated parser (automatically generated from the ABNF description of the grammar) as it processes a did-uri is automatic. i.e. there's not need to describe it English if you have a description using ABNF notation.  I hope this makes sense.

Best regards,
Michael




________________________________
From: Manu Sporny <msporny@digitalbazaar.com>
Sent: March 31, 2019 1:38 PM
To: W3C Credentials CG
Subject: A simpler approach to DID services and content-addressing

Apologies for missing the last DID spec call, some of us thought it had
been cancelled due to KNOW2019 and travel. I was reading the minutes
from the last meeting[1] and was happy to see two use cases identified
as driving factors for the DID URI scheme syntax (aka, ABNF) discussion.
I'm also attempting to build on the work that Drummond and Ken did
during RWoT8 (so you two may see some stuff that's familiar in here).

Let me try and summarize the use cases that seem to be driving the DID
URI scheme syntax:

1. Pat wants to publish blogging content in a way where they can switch
   service providers, but the relative URLs don't change. For example,
   <PORTABLE_SERVICE_PROVIDER_URL>/2019-03-01/lunch-in-barcelona
   ... which would be transformed to:
   <CURRENT_SERVICE_PROVIDER_URL>/2019-03-01/lunch-in-barcelona

2. Yael wants to publish content in a way that ensures the content
   integrity of the content. For example,
   <CONTENT_URL><SEPARATOR><CONTENT_INTEGRITY_CHECK>
   ... which would be transformed to:
   <PROTECTED_CONTENT_URL> (which returns tamper-evident data)

Now, let's narrow that down to the specification we're talking about,
which is the DID Specification. The pattern would change to something like:

<START_OF_DID><MAGIC><PATH>

and

<START_OF_DID><MAGIC><CONTENT_INTEGRITY_CHECK>

Much of this discussion has been around the <MAGIC> bit above. We know
what we want at the end, but there are many things that could go in the
middle. I should also note that these are two totally different use
cases and the group is probably thrashing because you're attempting to
solve both of them simultaneously. In this case, though, I think there
is at least one simple answer that doesn't require overly-complicated
microsyntaxes. So, here goes:

Use a colon-delimited keyword that you tack on to the end of a "bare DID".

That's it. Here's how it looks in practice for the two use cases above.

For the "Portable URL":

did:example:12345678:path:blog:/2019-03-01/lunch-in-barcelona

... which would be transformed to:

https://example.org/2019-03-01/lunch-in-barcelona

For the "DID with Content-addressing" (example assumes a Sovrin-like
requirement to get a content addressed schema):

did:example:schema:hl:z3aq31uzgnZBuWNzUB

... which would enable you to fetch things from that particular DID
Registry using content-based addressing.

The general matching pattern for the syntaxes are:

For the "Portable URL" use case:

did:<did-method>:<method-specific-id>:path:<service-id>:<service-path>

and for the "DID with Content-addressing" use case:

did:<did-method>:<method-specific-id>:<hashlink>

Note how the use cases are handled with things that you put *at the end*
of the DID URI syntax? This is on purpose for two reasons:

1. It ensures that DID Method authors have very broad control over what
   happens in <method-specific-id>, and
2. It enables decentralized innovation to occur while providing a clear
   adoption path into the core DID spec. (I think this is a nuance that
   many people might not get right now, but that's ok).

Here are two potential resolution algorithms for both use cases:

For the "Portable URL" use case:

1. Search for ":path:" from the end of the DID URL.
2. Split on the first two colons, you should have a 3-tuple:
   ("path", service-id, service-path).
3. Search the DID Document "service" property for a service
   with an "id" ending in "#<service-id" and save this value
   as "service-prefix".
4. Concatenate "service-prefix" with "service-path" and return
   this value.

For the "DID with Content-addressing" use case:

1. Search for ":hl:" from the end of the DID URL.
2. Split on the first colon, you should have a 2-tuple:
   ("hl", hashlink-value).
3. Dereference the DID URL and cryptographically hash
   the content.
4. Compare the hash of the content against the value
   of the hashlink. If the hashes match, the content is
   secure.

I believe the proposal above addresses all of the use cases raised by
Evernym and Sovrin. I also think it's compatible with Veres One and
IPFS-based DID Methods. The benefits of this approach are:

1. It ensures that DID Method authors have very broad control over what
   happens in their <method-specific-id>, and
2. It enables decentralized innovation to occur for these sorts of
   DID URI syntax extensions while providing a clear adoption path into
   the core DID spec, and
3. It doesn't require microsyntaxes more than what we have in the
   specification right now, and
4. The grammar parsing rules are extremely simple, and
5. It only requires one type of separator character for the DID URI
   syntax, the ":" character.

What did I miss? Why doesn't this work? I checked this against all the
current use cases (but did not elaborate on every one as this email is
long enough as it is). Would this work for your use case?

-- manu

[1]https://raw.githubusercontent.com/w3c-ccg/meetings/gh-pages/2019-03-28-did-spec/2019-03-28-irc.log

[2]https://github.com/WebOfTrustInfo/rwot8-barcelona/blob/master/draft-documents/did-spec-refinement.md#feature-refinement

--
Manu Sporny (skype: msporny, twitter: manusporny)
Founder/CEO - Digital Bazaar, Inc.
blog: Veres One Decentralized Identifier Blockchain Launches
https://tinyurl.com/veres-one-launches