Attacking a Measurement Device Independent Practical Quantum-Key-Distribution System with Wavelength-Dependent Beam-Splitter and Multi-Wavelength Sources

It is known that practical quantum key distribution system, because of the imperfect of devices, has sort of loopholes, so Eve can attack through these loopholes. The proposition of measurement device independent quantum key distribution protocol claimed to solve all the loopholes at the detector side. However the proof of MDI-QKD is based on the Hong-Ou-Mandel effect at 50:50 beam splitter. And with current experimental technology, a realistic beam splitter, made by fused biconical technology, has a wavelength-dependent property. Based on this fatal security loophole, the author propose a wavelength-dependent attacking protocol, which can be applied to practical MDI-QKD systems. Through this attacking protocol the author theoretical estimated that the eavesdropper could get 70% of the encoding information with a QBER of only 0.04.