Re: using PDFs as a VC container...

Thank you for the paper. That might allow anchoring PDF signed documents as
well. I will look into it in more detail !

Wrt "a standard approach for where/how to embed the VCs in the PDFs".. is
there something initiated on that already?  What would the next step be?



On Wed, Oct 21, 2020 at 4:03 PM Leonard Rosenthol <lrosenth@adobe.com>
wrote:

> Thanks – that helps!
>
>
>
> The iText library that you are using is fully capable of manipulating XMP
> and doing embedding and other techniques that I showed in my presentation.
> I haven’t looked at the state of Python PDF libraries in a while so I don’t
> know offhand which (if any) are XMP capable – though given that it has been
> part of PDF for almost 20 years and is now mandated for PDF 2.0 – I would
> hope they do!
>
>
>
> The approach you are using for hashing & verifying (with the post-hash
> addition and then removal) won’t work long term.  It happens to work with
> the tools that you are using – but it’s actually not a guarantee from a
> file format perspective.   The standard approach for embedding a signature
> into the thing you are signing (not just PDF but other formats) is a two
> pass approach involving the use of a “hole” in the file.  This is how PDF
> signatures have worked for 20+ years now.   Here is a good paper about it -
> https://www.adobe.com/devnet-docs/etk_deprecated/tools/DigSig/Acrobat_DigitalSignatures_in_PDF.pdf
>
>
>
> And yes, I agree that we need to come up with a standard approach for
> where/how to embed the VCs in the PDFs, how the signing & verification
> process works, etc.   Looking forward to it.
>
>
>
> Leonard
>
>
>
> *From: *Kostas Karasavvas <kkarasavvas@gmail.com>
> *Date: *Wednesday, October 21, 2020 at 3:26 AM
> *To: *Leonard Rosenthol <lrosenth@adobe.com>
> *Cc: *Credentials Community Group <public-credentials@w3.org>
> *Subject: *Re: using PDFs as a VC container...
>
>
>
> Hi Leonard and thank you for the comments!
>
>
>
> Please see inline.
>
>
>
> On Tue, Oct 20, 2020 at 9:13 PM Leonard Rosenthol <lrosenth@adobe.com>
> wrote:
>
> Very interesting, Kostas!   Thanks for sharing.
>
>
>
> I went to the repos below to see what you’ve done.  I peeked inside the
> PDFs and saw how you are storing data – while it works, it is definitely
> not a good approach.
>
>
>
> This is something that we would like to investigate further. Ideally, it
> would be improved as part of the VC-compatibility update that we want.
>
>
>
> Your knowledge would be very helpful on this. What approach would you
> recommend?
>
>
>
> And any python and JS libraries that can help insert/remove the metadata
> with the recommend approach?
>
>
>
>  What I didn’t see though is the actual source code for the hashing and
> embedding – because I am curious about the order of operations of those two
> operations since you couldn’t modify after hashing – yet that is what I see
> happening…
>
>
>
>
>
> Check
> https://github.com/verifiable-pdfs/blockchain-certificates/blob/5159a38d320280ab46092ab56450028435aaf6cb/blockchain_certificates/issue_certificates.py#L78
> <https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fverifiable-pdfs%2Fblockchain-certificates%2Fblob%2F5159a38d320280ab46092ab56450028435aaf6cb%2Fblockchain_certificates%2Fissue_certificates.py%23L78&data=04%7C01%7Clrosenth%40adobe.com%7C5c0d311ec8564d3ab9b808d87592ab9e%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C637388620093934005%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=QMluLJxeGvd0GYcNN4EUAg4cVLR%2FxalLm7G9rhvKsCM%3D&reserved=0>
>
>
>
> The documents are hashed and then their merkle root is constructed. The
> proof is inserted into the PDF at the end. During validation the proof is
> removed first, and then the document is hashed again to get the original
> hash that was anchored into the blockchain.
>
>
>
> We had thought of several alternative approaches but this seemed to be the
> best one.
>
>
>
> I see a lot of common ground. If it is of interest to you I would be happy
> to discuss further or even collaborate on this if it makes sense.
>
>
>
> Thanks again for the feedback!
>
> Kostas
>
>
>
>
>
> Thanks,
>
> Leonard
>
>
>
> *From: *Kostas Karasavvas <kkarasavvas@gmail.com>
> *Date: *Tuesday, October 20, 2020 at 11:42 AM
> *To: *Credentials Community Group <public-credentials@w3.org>
> *Subject: *using PDFs as a VC container...
> *Resent-From: *<public-credentials@w3.org>
> *Resent-Date: *Tuesday, October 20, 2020 at 11:40 AM
>
>
>
>
>
> Hi all!
>
> I would like to introduce the work that I have been involved with. I have
> been following the list/group for a while now and want to try to find the
> time to be more active   ... that, plus Leonard's presentation was a great
> opportunity/introduction :-)
>
>
> TL;DR:
> We have been using PDFs as a credentials' container and anchoring the
> document hashes on the blockchain. A blockchain proof (chainpointv2) is
> added in the PDF metadata which results in self-contained and
> self-verifiable PDF documents; the PDF is the only thing needed to view the
> credential and validate the credential*. There are open source validators
> that are trivial to use and/or host.
>
>
>
> The longer version:
> The University of Nicosia has been anchoring/issuing credentials (PDFs)
> for some of their courses on the Bitcoin blockchain since 2014. Back then
> the process was more manual/adhoc. In 2016 the solution was re-designed to
> (more or less) what we have today:
>
>
>
> - several PDFs are hashed and merklized, merkle root is anchored in the
> blockchain (bitcoin is used but it is blockchain agnostic)
>
> - merkle proofs, txid, etc. are stored in the respective PDF's metadata
> (using json format)
>
> - PDFs can be disseminated/stored as they always were
>
>
>
> Several companies already use PDFs so our solution fits into their
> workflows seamlessly. They had PDFs, they are anchored, and they still have
> PDFs**.
>
>
>
> A meta-protocol was designed to encode the data stored in the blockchain
> in a way that allows on-chain issuing/validation and revocation of the
> credentials. The process is described in detail in:
> https://ieeexplore.ieee.org/document/8525400
> <https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fieeexplore.ieee.org%2Fdocument%2F8525400&data=04%7C01%7Clrosenth%40adobe.com%7C5c0d311ec8564d3ab9b808d87592ab9e%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C637388620093944000%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=vh7Whif%2B5RCZq5AvEs5dmI68V2kFi8l%2F3M7ztZEBkOU%3D&reserved=0>
>
> (I can share if requested... not sure if the above is accessible to all)
>
>
>
> An open source implementation (with tools) can be found at:
> https://github.com/verifiable-pdfs/blockchain-certificates
> <https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fverifiable-pdfs%2Fblockchain-certificates&data=04%7C01%7Clrosenth%40adobe.com%7C5c0d311ec8564d3ab9b808d87592ab9e%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C637388620093944000%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=CWWrkf%2FMyjbsWgyg2bjs%2Bc9EzPZ7CuGfYbh0IcRukLk%3D&reserved=0>
>
> Validators at: https://github.com/verifiable-pdfs/validator-widget
> <https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fverifiable-pdfs%2Fvalidator-widget&data=04%7C01%7Clrosenth%40adobe.com%7C5c0d311ec8564d3ab9b808d87592ab9e%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C637388620093953999%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=hjPFeYBqaCj1UNpho%2B0WZxNrH3XfC%2FtVAlBPhtzuCrQ%3D&reserved=0>
> and  https://github.com/verifiable-pdfs/blockchain-certificates-validation
> <https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fverifiable-pdfs%2Fblockchain-certificates-validation&data=04%7C01%7Clrosenth%40adobe.com%7C5c0d311ec8564d3ab9b808d87592ab9e%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C637388620093953999%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=Cqq10SygqaGtlbk0kneOXujNmlc0eCZBWE2ZLcbB%2FXE%3D&reserved=0>
>
>
>
> From 2017 all of the credentials and diplomas issued by the University are
> issued using this platform. From 2019 the solution was commercialized
> (Block.co) to make it easier for potential clients (abstracting blockchain
> infrastructure, etc.). Several more clients/use cases came up rather than
> only educational credentials.
>
>
>
> We have looked into this in the past but it was frozen. Now we are again
> in the process of preparing/designing for VC-compatibility. We already use
> json format so using the VC format would be straight-forward in itself.
>
>
>
> However, I seem to be missing some parts, like how to formally define
> revocation mechanisms or how to formally include the blockchain proof. Is
> there a place where we can define our issuing / revocation mechanism so it
> can be reused/interoperable?
>
>
>
> Also it would be of great interest to see how we can properly use XMP that
> Leonard mentioned in a more standardized way in our solution.
>
>
>
> I would be happy to discuss further with anyone interested and thank you
> all for your time reading this.
>
>
>
> Regards,
>
> Kostas
>
>
>
> * Not unlike VCs other than the fact that the 'presentation'-layer is the
> verifiable container itself.
>
> ** The solution can apply to any file that supports custom metadata.
>
>
>
> --
>
> Konstantinos A. Karasavvas
>
> Software Architect, Blockchain Engineer, Researcher, Educator
>
> https://twitter.com/kkarasavvas
> <https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftwitter.com%2Fkkarasavvas&data=04%7C01%7Clrosenth%40adobe.com%7C5c0d311ec8564d3ab9b808d87592ab9e%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C637388620093963991%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=rZyucVKx%2FjqWxcKZZyU6F%2FrAHP0UpYyf7NdloVZs8p4%3D&reserved=0>
>
>
>
>
>
>
> --
>
> Konstantinos A. Karasavvas
>
> Software Architect, Blockchain Engineer, Researcher, Educator
>
> https://twitter.com/kkarasavvas
> <https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftwitter.com%2Fkkarasavvas&data=04%7C01%7Clrosenth%40adobe.com%7C5c0d311ec8564d3ab9b808d87592ab9e%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C637388620093963991%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=rZyucVKx%2FjqWxcKZZyU6F%2FrAHP0UpYyf7NdloVZs8p4%3D&reserved=0>
>


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