Document transfer

[shujingliew]

Indication of how ICL transfer document, e.g. the document is stored in the repository and API will provide the link for document access.

[monkeypants]

I have a suggestion.

1. ICL messages make reference to a unique document ID (but we do not put the document itself onto a ledger)
2. The country that sent the message provides access to the document via an API (e.g. GET /documents/{document_id})
3. the fact there is a message referencing the document, sent from country A to country B is proof (to country A) that country B is entitled to access the document. So, any party who can authenticate as country B is granted access to that document.
4. the document ID could be a cryptographic hash of the contents of the document. So, anyone who access the document is able to be certain that they have been given the correct, unadulterated copy of the document.

This way, the ledger contains pointers to documents, but those pointers are "cryptographic pegs" that effectively notarize the document.

[onthebreeze]

I've put more about this in the spec - see sequence story