Satellite Security: Quantum Cryptography Makes Dramatic Advance
 A significant leap has recently been made by a team of Northwestern University researchers working in collaboration with BBN Technologies to advance satellite security technology. Satellite security is an essential issue for the Department of Defense, which hopes within the next decade to launch its Transformational Satellite Communications System (TSAT), a network of military satellites that will enable every U.S. serviceperson on the planet to become a point in the Global Information Grid.
Until the TSAT is ready for implementation, however, the U.S. military reports that 80 percent of its communications are carried on commercial satellites. Hackers have attacked both military and commercial satellites in the past. Control of a British military satellite was commandeered by hackers, and satellite cable television service was interrupted by the political group Falun Gong in China. Many in the security industry see quantum cryptography as the greatest protection science has to offer to resist such intrusions.
Data encryption is ancient, older than Rome. But these are modern times, and the rise of computers and the availability of the Internet have made deciphering encrypted code much faster and easier. Standard encryption works by altering a packet of data and then sending it to a recipient who either already has the key or receives a dually coded key with the packet. The problem is the secret and safe distribution of the key.
Quantum cryptography eliminates this drawback. It codes and decodes zeros and ones at the level of an individual photon of light. The laws of quantum mechanics dictate that quantum particles are altered by mere observation, and therefore, if an intruder attempts to read or measure the code, the polarization state of the particle changes, creating errors that rat out the spy.
The research team is led by Prem Kumar, professor of electrical engineering and computer science at Northwestern’s School of Engineering and Applied Science, and the work is funded with a $5.4-million grant from the Defense Advanced Research Projects Agency (DARPA, famed for its gestation of the Internet). The researchers demonstrated the first quantum network in 2004, using the irreducible quantum noise in laser light to encode data, a technique called AlphaEta. This demonstration transmitted encrypted data between communicating parties, nicknamed Alice and Bob, who used a pre-shared encryption key.
Now, Kumar’s team has combined the AlphaEta technology with quantum key distribution to create the first truly quantum cryptographic data network. The interface of these two mechanisms allows super-high-speed optical transmission of encrypted data over long distances that is ultra secure, using a 1-kilobit key that refreshes every three seconds. The tests performed by the research team resulted in successful transmission from BBN headquarters to Harvard University in Cambridge, Mass., along a 5.5-mile SONET (Synchronous Optical Network) link. In another test, the signal was sent multiple times, eventually exchanging the key 300 times.
As the U.S. military moves forward to implement its plans for a completely integrated Network-centric force, quantum cryptography may prove to be a just-in-time answer to the question of satellite security.
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