Lasers Reveal Quantum Cryptography Flaw

By faking the quantum property of entanglement with the use of a laser, hackers managed to cheat the cryptography that was believed to be uncrackable.

According to Nature News, in theory you cannot intercept a quantum encoding without disrupting it, so the method of cryptography which uses the states of photons to encrypt data that's prepared for transmission should have been impenetrable.

It turns out that weaknesses in the machinery could allow hackers to bypass the security mechanisms, fact demonstrated by two independent groups in 2010.

"There have been some strong statements about quantum cryptography being robust against any attack. But it isn't that simple," reveals Christian Kurtsiefer, an expert on quantum optics at the Centre for Quantum Technologies of the National University of Singapore.

As a result, researchers tried to come up with better ways of protecting a transmission. Their latest attempt involves the incorporation of an impenetrable push-button test that should make sure the key is secure.

However, by shining a laser beam at the detector of one of the parties that share a quantum key, it can be tricked into registering somewhat normal values that cheat a standard entanglement Bell test that should clearly reveal if a quantum encryption key has been intercepted.

Due to equipment imperfections, lab-made Bell tests allow for a certain number of mismatches, this flaw being successfully exploited by hackers. If an ideal experiment should have been able to detect the fake correlations, the demanding machinery forbids such circumstances.

"These devices are so technologically demanding that to make building them more feasible, we sometimes think of sacrificing robustness," said Antonio Acín, a quantum physicist at the Institute of Photonic Sciences in Barcelona, Spain.

He claims that this last experiment proves that the loophole detection ignored so far by physicists must be looked at more seriously.