sudo apt install python-cryptography gajim gajim-omemo gajim-plugininstaller gajim-urlimagepreview
- gaim-plugininstaller: Make sure you have this so you can then easily add more plugins from within gajim.
- urlimagepreview: You want this - you might have to turn it on in the plugin settings
More download options (including Windows) are here.
Free server with secure group chat via OMEMO
You want to find a free XMPP server that is current enough to support OMEMO.
- Register on the website of this xmpp.social server.
- Add an account for it to Gajim, and connect.
- Create a new room! Set a password. Check members-only. You should be able to then turn on OMEMO!
Run your own server
XMPP mobile client
There's an android client that is really nice, and capable of OMEMO. It's not free. :-( But at least it's open source.
Also found an iphone client (untested).
Incabable XMPP servers
On these (older?) servers, Gajim always says "group must be non-anonymous and member-only" even though I'd set it that way.