Engineers hide messages in noise

There's a potential new form of steganography - the sending of messages in ways that leave no hint the messages even exists - that could lead to corporate data loss via CDs.

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There's a potential new form of steganography - the sending of messages in ways that leave no hint the messages even exists - that could lead to corporate data loss via CDs.

Steganography is just one application of technology being researched at Princeton University primarily to create instruments that can see through image noise to reveal hidden or obscured objects, says one of the researchers, Jason Fleischer, an assistant professor of electrical engineering at the school.

The engineers see the technology as potentially paving the way for improvements to radar systems, sonograms and stenography offering the possibility of allowing pilots to see through fog and doctors to look inside the human body without surgery

If the latest steganography application is brought to fruition, data could be stored on CDs in a way that renders it undetectable by conventional CD players. But with a specially designed player, the hidden data could be read.

In the case of steganography, if thieves could burn stolen data as hidden messages onto part of a CD, the rest could contain benign data that would lead corporate security professionals to think it was a run-of-the-mill CD containing unimportant data. Once the CD was outside corporate control, a special reader could reveal the stolen intellectual property.

The technology relies on a characteristic called stochastic resonance, the ability to refocus optical noise so it strengthens the optical signal that it is obscuring, Fleischer says. In the case of fog, images of objects are obscured because the water vapour diffuses the light bouncing off them.

The objects can be made clearer through the use of crystals whose refractive properties change depending on the amount of voltage flowing through them. Such a crystal sitting between an obscured object and the viewer can be tuned by applying a range of voltages until the optimal refractive property is found so the noise strengthens the signal enough to make it understandable.

This happens because when properly tuned, the crystal combines the energy of the light noise - the light diffused by the fog - with the weak energy of the signal - the light bouncing off the object obscured by the fog, making for a clear image of the object.

In the case of secret data on a CD, a coating on its surface would diffuse the signal from the data so a conventional CD player would interpret just noise and no signal. If a device containing a tunable crystal read the same CD, it could be adjusted to reveal the signal behind the noise, Fleischer says. "There could be a signal there, but unless you know it's there you wouldn't even know to look," he says.

In the lab, Fleischer and his colleague Dmitry Dylov used a ground-glass filter to simulate fog so they could control the statistical properties of the noise, but with refinement the same principles could be applied to natural environments, he says.

The researchers have filed for a patent on their discoveries and are looking to develop a proof of principle that a practical device could be developed from them. Their research was funded by the National Science Foundation, the US Department of Energy and the US Air Force.

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