ИСТИНА

The differential phase shift quantum key distribution protocol is of high interest due to its relatively simple practical implementation. This protocol uses trains of coherent pulses and allows the legitimate users to resist individual attacks. We propose new attack on this protocol which is based on the idea of information extraction from the part of each coherent state and then making decision about blocking the rest part depending on the amount of extracted information. It requires the ability to change the intensity of the states which reach Bob, and such type of attacks can be applied to other quantum key distribution protocols.