"The idea of Switzerland (released in alpha under GPL 3.0) is simple. You install the client on two computers, and set up a Switzerland server on a third. The EFF is providing a public Switzerland server to get people started. Then you send traffic back and forth between the two client machines. Each of them sends a hashed summary of the traffic it sees to the server. If the server notices a difference, that's pretty good evidence that someone between point A and point B is tampering with the traffic."
