XEP-0116: Encrypted Session Negotiation
Please tell me, why this XEP state is deferred?
WARNING: Consideration of this document has been Deferred by the XMPP Standards Foundation. Implementation of the protocol described herein is not recommended.
Because we have the only implementation :(
Unfortunately other clients aren't interested in ESessions any more. It has been Decided that the official XMPP end-to-end encryption method will be TLS over IBB or Jingle. There's been a lot of discussion on the security and standards mailing lists about this.
XEP-0116 is not a bad protocol and we'll keep it in Gajim for now, but probably remove it when XTLS catches on and we implement it.