On any given day, millions of e-commerce transactions send credit card and bank-account numbers zipping across the globe. To keep the bits of information private, companies such as PayPal use encryption software that employs mathematically intense algorithms. In a more advanced tactic, researchers now report sending a message embedded in light and masked by a wildly fluctuating laser beam. The message successfully traversed a commercial optical-fiber network.
In this new encryption strategy, a private message is converted into and travels as laser light. The information is hidden within a laser beam that undergoes chaotic intensity fluctuations. Such chaos-encrypted communication had already been mastered in laboratories. In the Nov. 17 Nature, an international team details how it sent such a message over 120 kilometers of fiber optics running throughout the city of Athens.
“The main achievement … is the fact that the transmission has been made over a commercially installed fiber network,” says Alan Shore of the University of Wales in Bangor. His team didn’t have to modify the optical lines. It was quite a “nice surprise” to see that the team’s lab setup translates well to a real-world setup, says Shore.
For the information transfer, the researchers used two virtually identical lasers as transmitter and receiver. The transmitter laser sent a chaotic signal along with the message to the receiver laser. Then, in a process called chaos synchronization, the receiving laser’s light output, which hadn’t been chaotic, synchronized with the chaotic signal from the transmitting laser.
“When two chaotic systems are coupled in a suitable way, they exert a form of control on each other,” explains Lucas Illing of Duke University in Durham, N.C., a researcher unaffiliated with the new study. Such synchronization also makes fireflies flash in unison and clock pendulums on the same wall match their swings.
Although scientists don’t understand why the receiver laser synchronizes with only the chaotic signal and not the embedded message, this synchronization permits the message to be extracted. To reveal the message, the researchers simply subtract the receiver’s output, which represents the chaotic signal, from its input.
The team transmitted roughly 1 gigabyte of chaos-encrypted information per second. This rate, Shore says, is comparable to those of most commercial transmissions of data. Moreover, the test transmission lost only about 1 byte in every 10 million, Shore notes.
The high transmission and low error rates are “what are so exciting about this research,” says Rajarshi Roy of the University of Maryland at College Park, who was not a member of the research team. Before this test, “nobody knew if [chaos communication] would work well” outside a lab, he adds.
The security offered by chaos encryption is currently no better than that of today’s standard software-cryptography schemes. However, the researchers suggest that it could be used in conjunction with security software to add another layer of privacy.
