Re: Putting pdf data into VCs

Hi Kristina / all,

First off, to my knowledge there is no standardized way to do this.

Indeed this is different from using the PDFs as the container. This is
something we have been thinking and although I don't have any answers, here
are my thoughts.

1) The institutions that provide the PDFs could also provide the
machine-readable metadata (this is what we optionally do with the PDF
container as well). There are decentralized storage solutions that won't
introduce a centralized PoF (with the assumption that the storage solution
is self-sustainable to guarantee long-term usage) so the pointer idea could
be feasible without compromising decentralization. Although less practical,
several such solutions could be combined for an even more resilient
solution. We have frozen investigations on this though. Did not seem that
important for the clients.

2) Yes, this can be done but the PDF won't be identical to the PDF that the
institutions provide unless they are constructed in an identical way. This
is not practical since each institution uses their own methods for that and
a lot just scan the physical degrees!  If they are not identical I don't
see the point of creating the PDF in the first place. Why not display the
metadata in HTML?

That is one of the reasons we opted for the PDF as a container. It
represented a digital version of their physical degrees; and a lot of these
institutions were issuing the PDF degrees anyway. The physical degrees
typically have several mechanisms to secure the document validity (like
holograms). For the digital version we anchor it into a blockchain. When
validating the PDF you will see the PDF (identical to the physical one) and
the blockchain verification details. This approach has the benefit that the
integrity of the exact PDF document that the institution has created is
becoming tamperproof. The issuing institutions do what they always did wrt
storing/disseminating their certificates (with potential improvements).

We add certain information into the PDF to achieve this. The PDF itself
(the visual representation) becomes a self-verifiable document and while we
currently use an adhoc json format we do intend to move towards VCs. The
idea is that a (universal) VC wallet would look for the VC in the metadata
of the PDF and validate it accordingly.

Finally, what one could also do is include a base64 (or equiv.) of the
whole PDF inside the VC. Thus, VC is the container and a specific visual
representation is attached. I believe this beats the purpose of having a
PDF in the first place but I would be open to counter arguments. Maybe it
will work in your use case but from my experience that would be contrary to
the workflow that these institutions typically have.

Hope the above are of some help,
Kostas



On Wed, Oct 28, 2020 at 9:03 PM Kristina Yasuda <
Kristina.Yasuda@microsoft.com> wrote:

> Hi all!
>
> Many educational institutions issue credentials (transcripts, graduation
> certificates, etc.) in pdf format, and we have faced an question of how to
> create VCs using claims in pdfs. Reaching out to the community is anyone
> has faced a similar issue and if there are standardized way/best
> practices to:
> 1) put data from pdfs into VCs while keeping integrity without relian on
> centralized party​? One option could be storing pdf files in
> centralized/decentralized servers and including a pointer to a file in a
> VC, but that would introduce a certain level of centralization.
> 2)  to reconstruct pdfs from claims in VCs?
>
> For example Modeling Educational Verifiable Credentials report (
> https://w3c-ccg.github.io/vc-ed-models/#biblio-obs-are-vcs) in section
> 1.5.3.1 shows the example of including pdf format in a VC, but how can
> the verifier reproduce a pdf record from the set of values in
> payload.data?
>
> This is a little different from using pdfs as a container, rather
> including information from pdfs into VCs.
>
> Thank you very much!
> Kristina
>
>

-- 
Konstantinos A. Karasavvas
Software Architect, Blockchain Engineer, Researcher, Educator
https://twitter.com/kkarasavvas