Gajim

Install

sudo apt install python-cryptography gajim

This includes the OMEMO plugin (I didn't need to go here.)

Plugins

• This first
• Then use it to add the image preview plugin.

More download options (including Windows) are here.

Configure

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

TODO

XMPP mobile client

There's a mobile client that is supposedly capable of OMEMO. It's not free.  :-( But at least it's open source.

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.

• https://www.kode.im/
• jabber.calyxinstitute.org