&gt; impossible<p>Difficult perhaps, certainly not impossible, and quite feasible if someone helps you. But I am not suggesting OpenPGP as an alternative for chat-apps for everyone; only for those who understand how to use the technology properly.<p>I mention OpenPGP and XMPP OTR because they are examples of open standards that do fulfil the principles outlined above. That is, to illustrate that it is certainly not impossible or infeasible to create such a technology. What is missing is a technology that does that, and allows anyone (regardless of technological prowess) to use them safely. It is a tough problem though.