Now, researchers Prof. Holger Boche and Dr. Rafael Schaefer from the Technical University of Munich (TUM) have devised a scheme that wrings provably strong security out of the otherwise vulnerable physical layer. This approach can prevent a would-be eavesdropper from even receiving the transmitted information. The starting point seems counter-intuitive: 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.
Normally, there is nothing to be gained by combining two channels with zero capacity: Zero plus zero equals zero. "But in this case", Rafael Schaefer explained, "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."
Similar results have been reported before, but only in studies of so-called quantum communications, and are not directly applicable to present-day technology. "To the best of our knowledge", Holger Boche stated, "this is the first example of super-activation - where zero plus zero is greater than zero - in classical communication scenarios." Holger Boche and Rafael Schaefer have also determined how to calculate the "secrecy capacity" of physical-layer channels designed to defeat active wiretappers. In addition, they have characterized the code structure and optimal transceiver design for implementing this scheme, a further step toward practical applications.
In recognition of this research, the Frankfurt-based Association for Electrical, Electronic and Information Technologies (VDE) has just awarded the prestigious Johann Philipp Reis Prize to Rafael Schaefer. The prize, named for the German inventor of the telephone, honours researchers under 40 for outstanding contributions to communications technology. Beginning in December 2013, Rafael Schaefer is continuing his work at Princeton University as a postdoctoral researcher with Vincent Poor, professor of electrical engineering and dean of the School of Engineering and Applied Sciences.
The following papers have been published:
This work was supported in part by the German Ministry of Education and Research (BMBF) and the German Research Foundation (DFG).