ИСТИНА

Differential phase-shift protocol quantum key distribution protocol uses tuples of coherent states with information encoded in phase difference between two successive states, so that blocking one particular state in the tuple causes errors on the receiver side. This configuration resists unambiguous state discrimination attack, a powerful attack that can be applied to a number of coherent-state QKD protocols. We will propose a new attack on this protocol based on the active beam-splitting attack. The key idea is that an eavesdropper tries to extract information from every state in the tuple, and in the case of fail they can send the unchanged part of original state. This makes the attack possible in the case when some of the states in the tuple were failed to measure, so the eavesdropper does not need to know every state in the tuple to perform this attack.