Swedish researchers reveal security hole

Swedish researchers reveal security hole

Quantum cryptography is considered a fully secure encryption method, but researchers from Linköping University and Stockholm University have discovered that this is not always the case. They found that energy-time entanglement – the method that today forms the basis for many systems of quantum cryptography – is vulnerable to attack. The results of their research have been published in Science Advances.

“With this security hole, it’s possible to eavesdrop on traffic without being detected. We discovered this in our theoretical calculations, and our colleagues in Stockholm were subsequently able to demonstrate it experimentally,” says Jan-Åke Larsson, professor at Linköping University’s Division of Information Coding.

Quantum cryptography is considered a completely safe method for information transfer, and theoretically it should be impossible to crack. Many research groups around the world are working to make quantum cryptography resistant to various types of disturbance, and so far it has been possible to handle the disturbance that has been detected. Quantum cryptography technology is commercially available, but there is much doubt as to whether it is actually used.

“It’s mostly rumours, I haven’t seen any system in use. But I know that some universities have test networks for secure data transfer,” says Prof Larsson.

The energy-time entanglement technology for quantum encryption studied here is based on testing the connection at the same time as the encryption key is created. Two photons are sent out at exactly the same time in different directions. At both ends of the connection is an interferometer where a small phase shift is added. This provides the interference that is used to compare similarities in the data from the two stations. If the photon stream is being eavesdropped there will be noise, and this can be revealed using a theorem from quantum mechanics – Bell’s inequality.

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