Nature.com posted an article describing that a hacking team around Vadim Makarov at the Norwegian University of Science and Technology in Trondheim have now cracked two commercial quantum cryptographic systems.Vadim Makarov said

Our hack gave 100% knowledge of the key, with zero disturbance to the system (..)

The Norwegian team attacked one system by ID Quantique (IDQ) based in Switzerland and another one by MagiQ Technologies from the U.S. It took two months to develop an unnoticable hack.

The Theory behind

Usually in cryptography the sender of a message is called “Alice”, the receiver is called “Bob”, and and evesdropper is named “Eve”. In quantum cryptography the message is consisting of photons. And according to the theory of quantum cryptography an evesdropper “Eve” trying to apply a man-in-the-middle attack leaves disturbances on the properties of the photons, sent by “Alice”, thus corrupting the message. But a corrupted message is easily detected by comparing parts of the message.

In Makarov and colleagues’ hack, Eve gets round this constraint by ‘blinding’ Bob’s detector — shining a continuous, 1-milliwatt laser at it. While Bob’s detector is thus disabled, Eve can then intercept Alice’s signal.
(..) That means that every time Eve intercepts a bit value of 1 from Alice, she can send a bright pulse to Bob, so that he also receives the correct signal, and is entirely unaware that his detector has been sabotaged. There is no mismatch between Eve and Bob’s readings because Eve sends Bob a classical signal, not a quantum one. As quantum cryptographic rules no longer apply, no alarm bells are triggered, says Makarov.

“We have exploited a purely technological loophole that turns a quantum cryptographic system into a classical system, without anyone noticing,” says Makarov.

Enjoy the whole article on Nature.com…