What is DIAS?
DIAS is yet another identity mechanism. It aims at allowing people to use their JID as a universal login in login-based systems like web forums, mail servers, etc., thus avoiding to create accounts and remember passwords again and again. The XMPP network, so, is used as a central user database, while benefiting from its decentralized, independant nature.
The DIAS mechanism is a 3-way communication that allows you to prove that you own a particular JID without disclosing the password. The idea is that you first ask, via XMPP, a unique ticket to a third-party "agent" trusted by the other side, then you show the ticket to the other side when you have it. The other side only has, then, to access the ticket information shared by the agent, in order to trustfully know your JID.
Please read the paper if you wish to learn more.