Scientists crack quantum cryptography

By Stuart Sumner
15 Aug 2011 View Comments
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Researchers in Singapore and Norway have teamed up to create a device that can crack quantum key distribution (QKD), a technique for securing digital communication originally designed to foil hackers.

QKD allows two remote parties to jointly create a shared secret key using the principles of quantum mechanics. Until recently, the process was thought to be virtually uncrackable.

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However, researchers at the Centre for Quantum Technologies (CQT) at the National University of Singapore, the Norwegian University of Science and Technology (NTNU), and the University Graduate Center (UNIK) in Norway changed that with the development of their device called Eve.

In the setup that was tested, the quantum key was created by two nodes sending light to one another one photon at a time. The key is developed using information taken from measuring the properties of the photons.

The principles of quantum mechanics dictate that the act of intercepting and measuring the photon in transit fundamentally changes its properties. In this way, the intended recipient of any message will know if it has been tampered with in any way.

However, Eve exploits a loophole in the technology and is able to invisibly intercept the key.

Eve intercepted the photons, then directed a laser at the photon detector, in effect blinding it. This meant that the detector was unable to tell that the photon it received had been changed, and accepted it as correct.

"This confirms that non-idealities in the physical implementations of QKD can be fully and practically exploitable, and must be given increased scrutiny if quantum cryptography is to become highly secure," said Vadim Makarov, a postdoctoral researcher at the University Graduate Center in Kjeller, Norway and a member of NTNU's Quantum Hacking group.

"We can not simply delegate the burden of keeping a secret to the laws of quantum physics; we need to carefully investigate the specific devices involved," added Christian Kurtsiefer, a professor at the Centre for Quantum Technologies at the National University of Singapore.

Eve, which has the appearance of an open suitcase full of wires and components, was built using purely off-the-shelf technology.

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