Is it possible to do revocable private messages in a decentralized system. My understanding it that the Zot protocol (used by Hubzilla) deals with this by keeping private data on the hub of the user sharing it, while public message can be mirrored to the hubs of any users receiving it. "Sending" a private message (or media file) to another user actually sends a notification to that user that they have permission to access it. When the receiver wants to access the message, their hub has to correctly identify them to the sender's hub, using credentials sent as part of that notification. But all of that is handled in the background, not a painful, confusing manual process users have to know about. See:
https://github.com/friendica/friendica/issues/2894#issuecomm...From what I understand of SSB,it works by distributing messages to receiving users as part of a blockchain, making all messages effectively public, even if not published with the goal of giving the public access. But maybe similar functionality could be added by setting up private "clubs" - pub servers set up by groups of users who know and trust each other - which would play the same role as a Hubzilla hub, storing private messages and displaying them to users who can authenticate correctly.