/vc-interview

Python SSI interview

A test project for a SSI Backend Developer position.

Overview

SSI movement yields a bunch of new buzzwords that are essential to understand in order to be able to smoothly walk around the technology underneath. This is also a pre-challenge task to accomplish.

SSI engages several parties (actors) to provide the truly decentralized and trustful network. Actually there at least a few approaches how to tackle the "trust" problem, but let's focus here on the classic model, where there are three essential roles: Issuer, Holder and Verifier and the Verifiable Data Registry that serves as a source of trust. See also https://www.w3.org/TR/vc-data-model/#roles .

A very well introduction to the concept can be found here: https://vimeo.com/459347107#t=520s .

Features / requirements

Let's try to mimic a part of this network and implement an Issuer and a Verifiable Data Registry. The basic features of this task would be to:

  • Get acquainted with the SSI core concepts to get the big picture;
  • Use LibSodium (you may use pysodium) in order to generate ED25119 key pair; Use py-multibase for Base58 encoding;
  • Use the generated public key and generate DID's and store its DID-document counterpart in a Verifiable Data Registry. Assume it is a HTTP service. Choose whatever storage method you will find suitable to store JSON documents (may be even a file on disk as long as you will be able to resolve DID document for given DID). The Verifiable Data Registry should expose two endpoints over HTTP protocol: GET /did/DID and POST /did with a body (DID document);
  • Assume DID-document has the following shape: https://www.w3.org/TR/did-core/#example-13-example-verification-methods;
  • Generate DID for the DID document -- here you may follow the did:sov rules;
  • Implement similar scenario to the one given here so there is an Issuer (who in this case is an University) that issues the Verifable Credential (saying that someone has graduated from this University);
  • Assume some DID for the Holder and use his DID in the VC above;
  • Sign Verifable Credential with the private key you have generated in the previous step;
  • Do not implement Holder, but instead, upload the VC from previous step into some place, ie. a gist or whatever you will find suitable for this purpose (this is essentially an oversimplification of the Holder role in this network, but let's keep the use case simple);

Caveats

Since it's more a concept app, it’s perfectly fine to make some compromises:

you can use whatever technology/framework is suitable for you (yet, please don't use a sledgehammer to crack a nut), the only interesing part is the enduser is able to run it and see the result; Don't be neither too generic nor too specific – don't polish it too much, but also keep focus on the code as well – your final product should be „just enough”.

If you don't feel prepared for the job, either get familiar with languages/technologies you'd consider useful here, or let us know you're not ready for it;

Your work should be available via GitHub as a public repository, commit often.

Value quality over quantity. And, finally, when in doubt – especially about the scope of the task – feel free to ask.