Or Tim Cook talk about how iMessage uses encryption.
Till then keep exploring and stay updated to all the new features coming out!! You can make a group Chat on Facebook Messenger in case you want to reach a specific group of friends.
That means the number of possible combinations is about 1 googol 10 to the 100th power - more possible combinations than there are atoms in the known universe.
But there's an even easier way.
You could just securely share a text file containing the link to your secure chat room using Keybase or Signal if you want to set those up.
I'm going to lay out the tools I would use if I wanted to form a group around a sensitive topic, or from inside a country with an authoritarian regime.