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Twente develops quantum method to safeguard data in multimode fibers

25 Feb 2020

Quantum Key Distribution security approach already established for singlemode systems.

Securing vulnerable computer systems and networks means paying constant attention to security to defend against cyber attacks. This vigilance also applies to the physical connections, the optical fibers connecting the computers.

By intercepting an optical signal passing through the fiber, a malicious hacker can access confidential data, or even take over a connection. But a new countermeasure, designed by researchers at the University of Twente, Netherlands, can defend against this type of attack.

The security method – developed for “multimode” glass fibers that can simultaneously carry multiple streams of data – is based on the quantum nature of light. The results are published in Optics Express.

Most glass fiber connections, especially long distance ones, are “single-mode”: they have one way in which light propagates through the fiber. “Multi-mode” fiber designs can, however, transport many wavelengths simultaneously, representing many channels and huge amounts of data transferred through a single fiber.

Multi-mode fibers (MMF) have a larger diameter and they transport various wave forms, for even higher data rates. Until now, they have been limited to being used at relatively short distances, in data centers, for example. Typical transmission speeds and distance limits of MMF are 100 Mbit/s for distances up to 2 km, 1 Gbit/s up to 1000 m, and 10 Gbit/s up to 550 m.

But the university says that these types of fiber “will be a good candidates for connecting the base stations of the new 5G standard telephone masts, for example. It is already possible to protect single mode fibers using the quantum properties of light.”

The UT researchers led by Professor Pepijn Pinkse have discovered a new quantum-based method of securing data transport through multimode fibers. The research was performed in the Complex Photonics Group, part of UT’s MESA+ Institute.

Programming light

Prof Pepijn explained, “A viewer looking inside a multimode fiber a would see a pattern of speckles of various intensities, caused by the different wave forms; the light is already scrambled.” The UT researchers add a new operation to this, known as “wavefront shaping”.

“The receiver can define a number of locations of light on the glass fiber at which the data has to reach him or her. The sender will program the light in such a way that it arrives exactly at the right spot. So, by shaping the light at the sender’s side, the receiver gets the desired pattern.”

In this way, one photon arriving at the right location is enough to deliver the message. As soon as the sender and the receiver agree, the data will be sent in this unique way. Using a mirror and a camera to pick up the light, somewhere along the fiber, doesn’t make sense: a hacker can do nothing with the patterns of photons at that location.

“Even if he is early and tries to intercept the agreement process,” said Prof Pinkse. “The negotiation phase between sender and receiver, may seem vulnerable. But for an interceptor, it remains unclear how the light will be programmed.” Sending a signal of his own to the receiver, would not help either: it would not be recognized.

UT’s approach is a new “multidimensional version” of the established Quantum Key Distribution technique used in singlemode fibers. Wave front shaping is a technology that was developed in Twente, for sending programmed light through a scattering medium like paint.

Its developers add that this approach “could lead to a credit card that is fraud-proof.” The strong scattering of light in paint resembles the scrambling of light in a multimode fiber. The researchers used the high level of unpredictability of scattering in their new method. Even in case of the doomsday scenario, in which quantum computers will be able to crack most of today’s security measures, this new approach will not be affected.

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