Boffins show off light-speed encryption

US computer scientists are preparing to unveil details of a technique that sends secret messages over public fibre-optic networks by hiding the transmission in background interference.

Bernard Wu and Evgenii Narimanov of Princeton University will detail their technique for "inexpensive, widespread and secure" transmission of confidential and sensitive data at this week's annual meeting of the Optical Society of America.

The system is based on hardware-oriented encryption, using the properties of an optical-fibre network to cloak a message. The sender transmits an optical signal that is so faint that it is very hard to detect, let alone decode.

The method takes advantage of the fact that real-world fibre-optics systems inevitably have low levels of "noise", random jitters in the light waves that transmit information through the network.

The new technique hides the secret message in this optical noise. The sender first translates the secret message into an ultra-short pulse of light.

A commercially available optical device (called an optical CDMA encoder) then 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 fibre-optic network.

The intended recipient decodes the message by employing 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 very secure: even if eavesdroppers knew that 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 out amid the more intense public signal.

"As the method uses optical CDMA technology, which is still undergoing significant research, I do not think any government or corporation is implementing this technique yet," said Wu.