Secure wire communicator development and results topic of plenary talk

May 10, 2007

COLLEGE STATION, Texas — His name is Kish. Laszlo Kish. And his invention could help 007 and other spies keep their communications secure and stealthy. Kish, a professor in the Department of Electrical and Computer Engineering at Texas A&M University, and his collaborators will discuss their recent work in secure communication during a plenary talk at the Fourth Annual SPIE Fluctuations and Noise Symposium May 20-24 in Florence, Italy. Kish has proposed that a simple pair of resistors on the ends of a communications wire such as a phone or computer line could keep eavesdroppers from intercepting secret messages. Added electronic disturbances (called "noise") or the natural thermal noise produced by the resistors (called Johnson noise) makes the scheme function, keeping the message unconditionally secret provided the bandwidth of the noise is kept sufficiently narrow. Picture the line connecting two telephones or computers. The sender and receiver at each end of the communication line each have two resistors of different resistance. Each randomly connects a resistor between their ends of the wire and ground, and then the sender begins transmitting the message. Using the natural thermal noise produced by the resistors provides stealth, making the communication difficult to discover. And building this unconditionally secure Internet-like network using this communicator is easy, Kish said. While the line of communication is open, both the sender and receiver monitor the electrical current and voltage fluctuations, or Johnson noise, in the line. While the sender and receiver use different resistances, an eavesdropper cannot determine the actual location of the resistors without injecting current into the communication channel and measuring the voltage and current changes in different directions. This added current gives the eavesdropper away, and the transmission is ended before the spy can extract more than a single bit of information. Then the eavesdropped bit is discarded. "The way the eavesdropper gets discovered is that both the sender and the receiver are continuously measuring the current and voltage and comparing the data," Kish said. "If the current and/or voltage values are different at the two sides, at any moment, that means that the eavesdropper has possibly broken the code of a single bit. Thus the communication has to be terminated immediately. "The same current/voltage monitoring method provides a natural defense against the so-called 'man-in-the-middle-attack,' which is another unique property of this system, because that type of attack hits other communication systems below the belt. The kind of man-in-the-middle attack we're talking about sets off the current/voltage alarm immediately even before the extraction of a single bit can be completed." Kish calls this the Kirchhoff-Loop-Johnson(-like)-Noise (KLJN) cipher, which he and his collaborators — Robert Mingesz and Zoltan Gingl of the University of Szeged (Hungary) — have designed, built and tested with the assistance of a Texas A&M Information Technology Task Force grant. The KLJN device can now be installed as a computer card similar to Ethernet network cards and has performed with 99.98 percent fidelity up to a range of 2,000 kilometers (1,250 miles) through a model line. This distance is about 12 times longer than the achieved range of direct quantum communication (160 km), Kish said. "Though there have been several theoretical attempts to break into the KLJN line," Kish said, "so far no proposed method has been able to challenge the total security of the idealized KLJN system. In the KLJN device we developed and tested, all measured security related parameters were superior to those of quantum communicators." Kish said that the dogma so far has been that only quantum communication can be absolutely secure and, according to some estimates, about $1 billion is spent annually on quantum communication research. But Kish has shown that classical communication measuring voltage and current can be more secure if done that wisely, and it can be done much more cheaply and more easily than quantum communication. And the KLJN communicator card is network ready. "Its security is superior to quantum communication, even at its idealized conditions, for several reasons," Kish said. "For example, the eavesdropper has to break a few thousands of bits to get discovered in an idealized quantum communication. In my idealized scheme, the eavesdropper can extract only zero bit without getting discovered." Kish directs the Fluctuation and Noise Exploitation Laboratory in the electrical and computer engineering department and is also a researcher in the Electrical and Computer Engineering Division of the Texas Engineering Experiment Station, the engineering research agency of the State of Texas and a member of The Texas A&M University System. TEES administers Kish's research.

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