This is an attempt to take a step back and summarize all proposed approaches to private messages (DMs, group chats, and general-purpose nostr-within nostr, including for large groups of people) for the purpose of building a secure, feature-complete, interoperable solution.
This topic has come up repeatedly over nostr's history, and has entered the limelight again because of HRF's e2e encrypted group chats bounty. The hope here is to get everyone on the same page and hammer out one or more NIPs that can incorporate the best parts of all proposed solutions so we can finally get secure messaging on nostr.
Please comment with thoughts, criticisms, missing proposals/implmentations, and I will update the gist as we go along.