They do, yes. It's certainly a requirement if channel binding is to work at all. Additionally there is this proposal to also detect attempted downgrade of the

They do, yes. It's certainly a requirement if channel binding is to work at all. Additionally there is this proposal to also detect attempted downgrade of the channel binding and SASL mechanism lists themselves: https://xmpp.org/extensions/xep-0474.html https://xmpp.org/extensions/xep-0474.html - which we're currently looking for expert eyes on, if you know any... :)