University of Massachusetts researchers have developed the world’s first covert communications system that hides a message, so someone listening into the conversation cannot determine if information has been sent or not.
The technique used uses a communication method called pulse position modulation. The method divides a unit of time into a number of time bands and each one of those bands corresponds to a symbol. The sender and receiver would have previously determined the band structure and corresponding symbols in private before sending messages. To further camouflage the messages, the team assumed the messages were sent using photons in a noisy environment and the messages cannot be distinguished from the noisy background.