The Next Battleground In The War Against Quantum Hacking

Ever since the first hack of a commercial quantum cryptography device, security specialists have been fighting back. Heres an update on the battle.

Quantum hacking is the latest fear in the world of information security. Not so long ago, physicists were claiming that they could send information with perfect security using a technique known as quantum key distribution.

This uses the laws of quantum mechanics to guarantee perfectly secure communication. And perfectly secure communication is what you get, at least in theory.

The trouble is that in practice the equipment used to carry out quantum key distribution has a number of weaknesses that an eavesdropper can exploit to gain information about the messages being sent. Various groups have demonstrated how quantum hacking presents a real threat to perfectly secure communication.

So in the cat and mouse game of information security, physicists have been fighting back by designing equipment that is more secure. Today, Nitin Jain at the Max Planck Institute for the Science of Light in Erlangen, Germany, and a few pals show how the changes still leave the equipment open to attack but at the same time reveal how the next generation of quantum cryptography could be made better.

In quantum key distribution, Alice sends information to Bob encoded in the polarisation of single photons. So she might send a sequence of 0s and 1s as a series of photons polarised horizontally and vertically. Bob can then use this information as the key to a one-time pad for sending information with perfect security. Hence the name quantum key distribution.

An eavesdropper, Eve, can only see the information Alice sends if she knows the directions that correspond to vertical and horizontal. Physicists call this the base of the system.

Without knowing the base, the information the photons carry will seem random. So a key part of the security of quantum key distribution comes from keeping Alices base secret.

Just over 10 years ago, hackers found a way for Eve to discover Alices base. All Eve has to do is shine a light into Alices equipment and measure the polarisation of the reflected photons. These will have bounced off the optical components that determine Alices base and so will be polarised in the same way. That gives Eve the crucial information she needs to decode the transmissions without Alice being any the wiser.

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The Next Battleground In The War Against Quantum Hacking