Advancements in Quantum-Based Encryption Technology

Can quantum cryptography provide secure encryption?

Almost 2 years ago, I wrote about a new type of encryption technology being developed that employs encryption techniques so strong that they might be virtually impenetrable. "Physics Today" magazine discussed the technology, quantum cryptography, which uses fundamental particles of light (photons) to establish random numbers at a transmitter and receiver. Those numbers can then be used as cryptographic keys to encode and decode data on a standard communications line. One of the companies involved in developing quantum cryptography, British company QinetiQ, recently announced an advancement in the technology.

Quantum encryption uses a photon's state as the key for encoding information. According to the Heisenberg uncertainty principle, it's impossible to discover both the momentum and position of a particle at any given instant in time. In theory, therefore, an intruder couldn't discover a cryptographic key based on particle state information; the intruder would need the actual particle to decipher any data encrypted with the key. If someone tried to intercept the digital key, the quantum state of the photon would change, alerting the intended recipient.

IBM scientists constructed the first working prototype of a quantum key distribution (QKD) system in 1989. At that time, they could transmit quantum signals only about 12.6" through open air. Today, fiber-optic cables can transmit the signals up to about 42 miles. Now, QinetiQ has successfully transmitted quantum encryption-based data over a distance of about 14.5 miles without fiber-optic cable.

Although photons aren't suited to carry an actual message, according to QinetiQ, quantum key technology works because photons can establish identical random numbers at both the transmitter and receiver. "These large random numbers can then be used as 'cryptographic keys' for encoding and decoding data on a standard communications link."

QinetiQ's testing took place in the mountains of Germany, where the company works in conjunction with Ludwig Maximilians University in Munich. Teams on two mountaintops successfully transmitted quantum encryption keys through the air, then decrypted the data successfully using the keys. They demonstrated that one can use the technology to send encryption keys over increasing distances without using fiber-optic cables.

The researchers used a green laser to accurately align the transmitter and receiver located on the mountaintops. The transmission setup involved a transmitter that sent a 10MHz beam of light between 1 to 2 yards in diameter. The receiver was a commercial telescope with a photon-counting module mounted on the end. Polarizing beam splitters in the module determined the polarization of the received photons, and thus, the bit value of those photons. The researchers then used the bit values to determine the quantum keys that encrypted and decrypted associated data transmitted over a separate traditional communication link.

QinetiQ's goal is to use earth-orbiting satellites to transmit keys around the globe. "Having demonstrated that it's possible to send a key through the air over long distances, it should soon be possible to send a message from the ground to an orbiting satellite," explained Professor John Rarity, leader of the QinetiQ team developing this technology. "We should then be able to relay quantum-encoded keys around the globe, providing absolutely secure communications ... using well established communications systems \[to move any associated encrypted data\]." To learn more about how QinetiQ structured its tests, read the press release on the company's Web site

The technology is intriguing, although we have much to learn about its capabilities and potential flaws. Currently, at least one company, Switzerland-based id Quantique, offers fiber-optic equipment based on the technology. For more about the current state of QKD development, plug the term into your favorite search engine.

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