"Researchers at the Technische Universität München (TUM) have proven that wireless communications can be made more secure through a novel approach based on information theory," announced TUM Monday. Eavesdroppers can currently listen into wireless and mobile phone data without disturbing either the message or the channel. "Thus the last line of defense today is encryption, aimed at making the intercepted message difficult if not impossible for anyone other than the intended recipient to decipher. But cryptographic techniques are being rendered less and less secure by advances in computing."
Now, however, researchers Prof. Holger Boche and Dr. Rafael Schaefer have demonstrated provable security obtained from the physical layer of communication. The method is counter-intuitive and involves information theory and zero capacity channels. "The scheme uses two physical channels – that is, frequency bands in a wireless system – that are inherently useless, each being incapable of securely transmitting a message," says TUM.
Intuitively, combining one zero-capacity with another zero-capacity should result in zero capacity. “But in this case,” Schaefer explains, “it’s as if we’re getting a positive result from adding zero to zero. We find that we are able to ‘super-activate’ the whole system, meaning that combining two useless channels can lead to a positive capacity to transmit confidential messages securely.”
Superactivation is not unknown in quantum theory. It's the combining of zero capacity quantum channels to produce a channel with positive capacity; but is not yet applicable to current technology. But what Boche and Schaefer have achieved "is," says Boche, "the first example of super-activation – where zero plus zero is greater than zero – in classical communication scenarios.”
The research brings the development of provably quantum-like secure wireless communications that do not rely on encryption much closer. For his part in the research, Schaefer has now been awarded the Johann Philipp Reis Prize (named after the German inventor of the telephone) awarded for outstanding contributions to communications technology.