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Review of OBI Badges vocabulary

From: Manu Sporny <msporny@digitalbazaar.com>
Date: Tue, 20 Jan 2015 00:27:23 -0500
Message-ID: <54BDE73B.4040604@digitalbazaar.com>
To: Credentials Community Group <public-credentials@w3.org>
I took an action[1] last week to review the OpenBadges spec at:

http://standard.openbadges.org/

Here's the first rough review:

> Open Badges Standard

I don't think we should be calling this a standard yet. I know the BA
wants to call it a standard, but that word means something special at
the W3C, IETF, ISO, OASIS, etc. I think we'll get significant and
unnecessary push-back from W3C comms and legal about this if we proceed
w/ any language that positions this document as a standard. I know there
is a disclaimer in the doc, but I don't think that'll convince W3C that
people will understand the nuance that statement is drawing.

> Portable digital credentials

Badges, credentials, microcredentials - we need to get our terminology
straight between the groups.

> embedding it into portable image files as digital badges

The image file thing is a non-goal for Digital Bazaar, maybe we can
reword it to "optionally embedding"? The important bit is the data
format, not where you can stuff the data format, no?

> JSON-LD context (v1.1)

Lots of thoughts on the context, but don't have time to delve into all
of them right now. Maybe that'll be a separate review. In general it
looks like class names (words starting w/ caps) are intermixed with
property names (lowercased names). The definition of 'type' is slightly
confusing, unless the OBI type subclasses rdf:type. obi:validation seems
like it might need to use JSON-LD framing to work for non-trivial examples.

> They are published as JSON for interoperability.

Why not as JSON-LD?

> Badge Baking Hosted Verification Signed Verification

This sort of content isn't usually found in a vocabulary document. It's
a part of a spec, like the Identity Credentials spec. I suggest moving
this stuff out to a separate document.

> Hosted Verification

I think we should be focusing solely on digital signatures for
verification. The whole hosted model is very problematic when you start
working with credentials that are mission critical.

> Signed Verification

-1 to JWS:

http://manu.sporny.org/2013/sm-vs-jose/

> Assertion

> uid

You don't need a UID if you follow Web Architecture principles. There is
just an identifier, which is a URL. That is both globally unique and the
identifier can be generated locally.

The question is whether to map this to @id, or to have a new 'id' value
that is a URL and relegate uid to "legacy" status.

> recipient

+1 for this language over credentialee

> badge

The fact that both recipient, badge, and a few other properties are both
machine-readable and change is bad news for deep validation of badges.
This is going to cause a huge problem for digital signatures on badges.

We're either going to need both 'badge' and 'badgeHash', or you're going
to need to deep nest the IdentityObject, BadgeClass, and
VerificationObject. If you don't do that, for example, the BadgeClass
could vary wildly over time w/o invalidating the digital signature
(which it should).

> verify

Again, I disagree with this approach to verification. The Hosted model
is not something that Digital Bazaar would be interested in supporting
in any other way than legacy support.

> issuedOn - DateTime - Either an ISO 8601 date or a standard 10-digit
>  Unix  timestamp.

no unix timestamps, they're incredibly difficult to read/debug and don't
really provide any benefit these days. Make the dates and times human
readable.

> This must be a PNG or SVG image, and should be prepared via the 
> Baking specification.

-1 to Badge Baking being in the vocabulary document, or a core
specification.

> IdentityObject

> identity

This should be an IRI or URL. Assigning badges to people's names is fine
for low-value badges, but again, Digital Bazaar doesn't really have an
interest in low-value badges.

> type

Could be confused with rdf:type and JSON-LD's @type. E-mail addresses
make bad long-term identifiers.

> hashed

-1 to hashed identifiers. Identifiers, especially in Linked Data, need
to be dereference-able.

> VerificationObject

Verification should be digital-signatures based. We could still support
this for legacy purposes.

> BadgeClass

+1 to the content of a BadgeClass, but why not move most of this up into
the top-level badge object? Doing so saves a great deal of headache wrt.
verifying the digital signature because you push developers to include
all of the important information in the badge itself (without requiring
an external dereference to figure out if the badge is valid).

> IssuerOrganization

> image

markup looks malformed.

> revocationList

If we used URLs to identify badges, just dereferencing the badge URL
would enable you to see if it was revoked or not.

> For example, if the issuer at example.org wants to add a foo
> property to the assertion, the property name should be example:foo,
> or preferably a dereferencable IRI describing the property, such as 
> http://example.org/foo.

"example:foo" would be dropped by a JSON-LD processor that doesn't have
"example:" mapped. The digital signature wouldn't cover the property. In
fact, things that don't map to the JSON-LD context are not going to be
signed and are thus not protected from tampering. This bit looks like it
needs more work as I think it creates a security hole in the spec.

> Signed Badges

Agree that signed badges are very important, disagree that JWS is the
best path forward.

In general I think the following changes need to be made to the
specification:

1. The vocabulary should be extracted out into a separate document.
2. Signing could just re-use the Linked Data Signatures specification.
3. Everything else should go into an OBI spec (hosted, structure of
   badges, extensions, etc.)

Unfortunately, there are a number of contradicting opinions above, so
we'll need some discussion to tease out where the group wants to go with
things like flat badges vs. nested information wrt. digital signatures.
Whether or not extensions need JSON-LD framing, or if we just require
extensions to do shallow nesting + JSON Schema checking against
compacted JSON-LD data for now. We may also want to talk about freezing
1.1 and ensuring that the entirety can be expressed in an Identity
Credential and then move to the Identity Credentials format for OBI 2.0?
Just some food for thought, talk w/ everyone on the call tomorrow.

-- manu

[1] http://opencreds.org/minutes/2015-01-13/#88

-- 
Manu Sporny (skype: msporny, twitter: manusporny, G+: +Manu Sporny)
Founder/CEO - Digital Bazaar, Inc.
blog: The Marathonic Dawn of Web Payments
http://manu.sporny.org/2014/dawn-of-web-payments/
Received on Tuesday, 20 January 2015 05:27:48 UTC

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