Yeah. Basically Signal protocol over XMPP. It uses the XMPP server for the stored/delayed cryptographic state which is why you need a server that can do PEP (Pe

Yeah. Basically Signal protocol over XMPP. It uses the XMPP server for the stored/delayed cryptographic state which is why you need a server that can do PEP (Personal Eventing Protocol) if you want to do OMEMO. OMEMO has pretty much replaced OTR in the clients so if you want simple/stateless you are left with one of the two PGP flavours.