For your eyes onlyKeeping messages over the Internet secure by making them faint

Published 11 October 2006

Wireless and Internet communication is vulnerable to eavesdropping and theft; traditional methods of keeping messages secure — encryption and scrambling — may be expensive to implement; two Princeton researchers suggest a new technique to keep transmissions safe, a technique which relies on the properties optical-fiber networks

Wireless communication and the Internet have many beneficial effects, but from the beginning both have been dogged by one concern: Security. It is not an accident that cyber crime and identity theft have grown apace with the increasing reliance on digital records and wireless transmission of business and other transactions. Now there is a new technique to send secret messages under other people’s noses without the messages being detected. This may sound futuristic, but it is available now and may be implemented instantly using existing equipment and infrastructure. The annual meeting of the Optical Society of America is taking place this week in Rochester, New York, providing Bernard Wu and Evgenii Narimanov of Princeton University with the occasion to present a method for transmitting secret messages over existing public fiber-optic networks, such as those operated by Internet service providers. If adopted, the new technique would allow inexpensive, widespread, and secure transmission of confidential and sensitive data by governments, businesses, and individuals.

Wu and Narimanov’s technique does not rely on encryption and scrambling, the traditional ways to keep communication secret. Rather, they suggest a more hardware-based form of encryption, a method which relies on the properties of an optical-fiber network to conceal a message. The key is for the sender to transmit an optical signal which is so faint that it is very difficult to detect, let alone decode. The method exploits the fact that fiber-optics systems have low levels of noise, that is, random jitters in the light waves which transmit information through the network. The new technique hides the secret message in this optical noise.

Here is how it works: The sender first translates the secret message into an ultrashort pulse of light. Then, a commercially available optical device (an optical CDMA encoder) spreads the intense, short pulse into a long, faint stream of optical data so that the optical message is fainter than the noisy jitters in the fiber-optic network. The intended recipient decodes the message by using information on how the secret message was originally spread out and using an optical device to compress the message back to its original state. The method is highly secure: Even if eavesdroppers knew a secret transmission was taking place, any slight imperfection in their knowledge of how the secret signal was spread out would make it too hard to pick the secret signal out from amidst the more intense public signal.

Wu believes that government and businesses would have the greatest use for this technique, but consumer applications are possible as well. Consumers, for example, may transmit sensitive data through fiber-optic lines for a banking transaction. “This would not be a primary transmission scheme one would employ 24/7, as the price for enhanced security is a lower transmission rate,” Wu adds. Yet, since consumers send encrypted information to banks only intermittently, “the stealth method is practical” for that purpose, he says.

-read more in Bernard Wu and Engenii Narimanov, “A Method for Secure Communications over Public Fiber-optical Network,” Optic Express 14, no. 9 (1 May 2006): 3738-51