High-latency messaging via lego robot courier
Wireless doesn’t necessarily have to mean radio waves. If you’re worried about people listening in on your conversations, why not use a courier instead?
This is a solution I developed as part of my degree programme at the University of Aberdeen. At each end are two VT100 terminals, these connect to the robot through tin foil contacts at each end of the board. A switch on the robot lets it know that it’s hit the wall and (hopefully) docked with the contacts. The robot then spits out any message it was carrying and asks for another message by displaying a prompt on the terminal and then storing the input. Once the Enter key has been hit, it travels back again to the other terminal.
Remember though, no solution is truly secure, this is still open to man in the middle attacks and the robot can be easily confused by anyone with enough black tape.