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Eavesdroppers begone: New quantum key distribution technique is impervious to noise

Posted June 12, 2014
Principle behind the proposed quantum cryptography protocol
Principle behind the proposed quantum cryptography protocol. The final single bit value is calculated from many bits through a pair of numbers {i,j} announced by the receiver, Bob. The upper panel corresponds to the actual scheme, in which Bob measures the wave-like nature of the received light sent by Alice to learn the final bit value. Notice that the value of {i,j} might be controlled by an eavesdropper (Eve) through the signal (II) fed to Bob’s measurement process M, so looking at this panel alone, the security is ambiguous. If Bob now measures the particle-like nature of the received light, he no longer learns the final bit but can still exactly produce the same pair {i,j} Lower panel: Here it is seen that {i,j} is directly randomized by the random number generator. Therefore, the possibility that Bob could have measured the particle-like nature of the received light ensures that the randomness of {i,j} is not rigged by Eve. Credit: Toshihiko Sasaki

Cryptography – the art and science of providing secure communications – typically employs three methods to authenticate users and prevent data theft: secret key (symmetric) cryptography, which uses a single key for both encryption and decryption; public key (asymmetric) cryptography which uses different keys for encryption and decryption; and hash functions, which employs a mathematical transformation to irreversibly encrypt information. That being said, quantum cryptography relies on the laws of quantum mechanics to secure private information exchange, specifically through quantum key distribution (QKD) of a random bit sequence, in which an attempt to eavesdrop on the encoded quantum states causes a detectable disturbance in the communications signal. Historically, high-precision monitoring of the disturbance decreases efficiency – but recently, scientists at The University of Tokyo, Stanford University and National Institute of Informatics (Tokyo) proposed a QKD protocol based on an entirely different principle.

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