Ask HN: Resources on Building a Syncing Engine?

Hi everyone, I'm building your standard CRUD app as a toy project to explore some fields I'm interested in.

My goal is to make the app local-first with the option to synchronize to a central server and other devices. The data should also be E2E encrypted, meaning that users should input their passwords in order to decrypt the data downloaded from the server.

What I'm asking in this question are resources on how to learn anything relevant to the problem at hand. Good resources on CRDTs, distributed systems, etc., you name it.

I'm also not looking for finished products themselves (e.g. Couchbase or CouchDB), as my goal is to learn this stuff and implement myself a sync engine specific to my app. However I'd love to read resources about the implementation behind these products.

Thanks!