  Unconditional security of quantum key distribution protocol can be guaranteed
by the basic property of quantum mechanics. Unfortunately, the practical
quantum key distribution system always have some imperfections, and the
practical system may be attacked if the imperfection can be controlled by the
eavesdropper Eve. Applying the fatal security loophole introduced by the
imperfect beam splitter's wavelength dependent optical property, we propose
wavelength-dependent attacking model, which can be applied to almost all
practical quantum key distribution systems with the passive state modulation
and photon state detection after the practical beam splitter. Utilizing our
attacking model, we experimentally demonstrate the attacking system based on
practical polarization encoding quantum key distribution system with almost
100% success probability. Our result demonstrate that all practical devices
require tightened security inspection for avoiding side channel attacks in
practical quantum key distribution experimental realizations.
