Very complicated but it's the only option for large (100+ppl) encrypted private groups. In theory, it requires two centralized services, which we don't have in Nostr. But I think nostr:nprofile1qqspwwwexlwgcrrnwz4zwkze8rq3ncjug8mvgsd96dxx6wzs8ccndmcpz4mhxue69uhhyetvv9ujuerpd46hxtnfduhszrnhwden5te0dehhxtnvdakz7qg3waehxw309ajhjetn9enrw73wd9hsqwhj0h found a way around these restrictions. It would be great if it worked. I am still unsure what relays, the public and users can track from one another over time. But it will likely require a Tor-like IP hiding system to make sure relays can identify keys when the app is doing REQs with multiple filters.