There exist some secure schemes where keys are not exchanged, and those would be effectively outlawed. https://en.m.wikipedia.org/wiki/Three-pass_protocol http

There exist some secure schemes where keys are not exchanged, and those would be effectively outlawed. https://en.m.wikipedia.org/wiki/Three-pass_protocol https://en.m.wikipedia.org/wiki/Three-pass_protocol Nevermind that increasing the parties being attacked almost always makes the job easier not harder. See the TSA master key debacle for an example of how adding a third party master weakened the security and allowed statistical analysis to break the lock.