W3C home > Mailing lists > Public > public-credentials@w3.org > February 2022

Re: CBOR-LD for VC

From: Manu Sporny <msporny@digitalbazaar.com>
Date: Tue, 15 Feb 2022 09:36:07 -0500
To: public-credentials@w3.org
Message-ID: <7316d008-4a26-6d83-acd2-f1e59156ab60@digitalbazaar.com>
On 2/14/22 12:48 AM, Anders Rundgren wrote:
> Continuing the CBOR thread but now with dedicated subject line. I'm not 
> much into "LD" but obviously you should be able to create a CBOR-LD.

For those of you that are not aware, Anders fought bravely at IETF for close
to a decade to get the JSON Canonicalization Scheme published as an RFC:


As he mentions elsewhere in the thread, there are people at IETF that are
strongly against doing any form of data canonicalization (taking input data
and formatting it into a standard format). Those same people tend to block any
progress on work of that nature in any IETF WG.

I was shocked (in a good way) when Anders became successful in publishing
RFC8785 becoming the first person to get a generalized canonicalization scheme
through IETF in 20+ years. I've been wanting to sit down with him for years to
hear the story about how he accomplished that:


... and that's for the simplest type of canonicalization scheme.

As many of you know, the Data Integrity work (was: Linked Data Signatures),
has two canonicalization schemes that are used... JCS (RFC8785) and URDCA2015
(RDF Dataset Canonicalization -- which uses JCS for canonicalizing JSON data).
The W3C is going to pick up standardizing that work in the next couple of
months (once the charter votes happen).

> The only real stumbling block I have found is that the "Guardians of CBOR"
>  consider URLs as type identifiers a bad thing because: - The intention
> was (and is) that you register application-specific nnn() tags with IANA -
> URLs open the possibility reading CBOR schemas in run-time which is a known
> XML foot-gun

Yep, that's the same centralized thinking that has been common at IETF for
well over two decades now. "Innovate through us." being the subtext. While it
has gotten the Internet to where it is today, it's not a good recipe for
decentralized innovation (which admittedly has it's own pitfalls).

Everything runs through centralized registries that have gatekeepers that stop
canonicalization work due to legitimate scars caused by XML Canonicalization
(which is a very different problem, but it's nearly impossible to have a
rational conversation about it at IETF).

> Decentralized URLs as type identifiers are (IMO) a necessity for a lot of 
> systems. Regarding reading schemas in run-time: there will always be people
> who do not understand how to write secure software but will do it anyway.

Yep. The solution there has always been simple: "DO NOT load schemas at
runtime in production systems. Ship software with the schemas locked down."

> As I wrote in another thread, using COSE signatures (or encryption) is 
> something I wouldn't do.  Using COSE public key and algorithm identifiers 
> is though perfectly workable.

I'd be interested in hearing more about why you think this, Andrews.

> Regarding possible COSE-LD signatures I would consider a solution where 
> signatures only protect the actual bytes transferred, and feature the LD 
> part as a hash.  That is, validation of LD canonicalization would be an 
> optional step.

Now there is a really compelling idea (for those working in CBOR). I wish I
had more time to chase that idea down. My instinct says that the problem with
that approach is that you have to fully commit to working in CBOR. The CBOR-LD
approach doesn't require you to commit to working in JSON-LD or CBOR-LD... you
can switch between the two w/o having to re-do all of your digital signatures.
There is now some work happening on YAML-LD[1], which is going to be able to
benefit from all the benefits/specs behind JSON-LD or CBOR-LD once it becomes
a thing in the world.

This means that people can losslessly convert graph-based data (Verifiable
Credentials, social networks, supply chain dependencies, etc.) between JSON,
CBOR, and YAML... including all the digital signatures w/o having to re-sign
the data. That's the real power of canonicalized forms.

-- manu


Manu Sporny - https://www.linkedin.com/in/manusporny/
Founder/CEO - Digital Bazaar, Inc.
News: Digital Bazaar Announces New Case Studies (2021)
Received on Tuesday, 15 February 2022 14:36:26 UTC

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