Security system for quantum cryptography keys demonstrated

Science : Quantum cryptography applies principles of public-key cryptography to communications systems that transmit information encoded on individual photons. However, in 2010 it was found that the key-sharing signals could be intercepted and reproduced in such a way that the security was compromised without the sender or receiver knowing. Last year, Hoi-Kwong Lo of the University of Toronto and his colleagues proposed a system that prevents the interception: The sender and receiver send randomly polarized signals to a third party. The third party indicates whether the polarizations are at right angles. If they are, the receiver adjusts their polarization to align with the sender, forming the key. Neither the sender nor the receiver needs to measure polarizations on future messages, so any interception that measures the polarization would corrupt the signal. And now two independent groups led by Wolfgang Tittel of the University of Calgary in Canada and Jian-Wei Pan of the University of Science and Technology of China have demonstrated the third-party system’s viability. Other solutions to signal interception have also been developed, but the fact that Lo’s proposal is usable gives quantum cryptography systems another option to ensure their security.