Fascinating thoughts. The group (id) is just another npub. A shared private inbox.
I still marvel at the concept of nostr:nprofile1qqsryw70hw5qf38vcqddvuwc4kggzh8yty485gyv3qxh8zhyqg0tz4qpz4mhxue69uhhyetvv9ujuerpd46hxtnfduhszyrhwden5te0dehhxarj9ekk7mf0qy88wumn8ghj7mn0wvhxcmmv9u9nm47p
When many people know the same private key, they enjoy fully anonymous group DMs and group announcements.
People who know the key can sign and encrypt messages to it, which only the other group members can read, but even they don't know who actually signed the message. It's a refreshing change to not know the identity of a speaker, you focus on the message, not the messenger, and high quality ideas are generally promoted.
Likewise anyone in the group can sign a kind 1 and make public posts to the nostr, where again nobody knows which exact individual signed this message.
This is such a trivial solution, and it's amazing how well it actually works. Yet we can apply zero knowledge cryptography to have more secure access rights while still ensuring anonymity of the participants.
Discussion
A shared nsec could also be deterministically rolled forward (ratchet) in order to decorrelate the group msg npub(s). Then it becomes conceptually similar to nip 104 mls.
But I really like the simplicity of "shared npubs" as a building block to build other things than private chat rooms. It is already there, interoperable and supported by most clients.
Exactly.