Scientists Overcoming Quantum Encryption's Distance-Related Hurdles

Scientists have hoped for years that quantum encryption would become an unbeatable method for transmitting encrypted data. The problem has been making it work over long distances. Now that hurdle is showing signs of falling.

For the most part, the cryptographic battlefield has taken place in mathematics, with senders of data trying to create encryption algorithms too complex for the snoopers to crack. Quantum encryption, however, could shift the struggle to the field of physics and lead to encryption that's more secure than the public key cryptography technology often used today.

Quantum encryption's chief impediment has been its inability to send infor- mation great distances. Scientists at the National Institute of Standards and Technology, Los Alamos National Laboratory, and Albion College in Michigan revealed last month that they generated and transmitted secret quantum keys over 115 miles of fiber-optic cable during an experiment last year--the farthest such information has traveled.

Scientists at NIST, Los Alamos, Northwestern University, and IBM have been trying to solve the same problem for decades. The first experimental quantum encryption prototype, created in 1991, was able to send information a mere 32 centimeters.

With quantum encryption, the sender encodes information on an individual quantum particle, such as a photon or electron. The recipient has information about this quantum particle's characteristics, its size, or level of polarization, which lets the recipient interpret the information. Quantum encryption is resistant to eavesdropping by a third party because, according to the laws of physics, a photon can't be intercepted without changing its quantum state. Any attempt to eavesdrop on encrypted data would be detected immediately.

The technology would resist "all future kinds of attacks," says Carl Williams, coordinator of the NIST quantum information program.

NIST's photonic sensors, developed by NIST physicist Sae Woo Nam, were the key to the experiment's success. The distance light can travel over fiber-optic cable depends on the quality of the glass fibers in the core of the cable. NIST's photon sensors were 45% more efficient than commercial ones.

Still, challenges remain for quantum encryption. It isn't compatible with public key encryption systems. It also still needs to stretch across greater distances in order to be practical for most businesses.