Device calibration impacts security of quantum key distribution
  Characterizing the physical channel and calibrating the cryptosystem hardware are prerequisites for establishing a quantum channel for quantum key distribution (QKD). Moreover, an inappropriately implemented calibration routine can open a fatal security loophole. We propose and experimentally demonstrate a method to induce a large temporal detector efficiency mismatch in a commercial QKD system by deceiving a channel length calibration routine. We then devise an optimal and realistic strategy using faked states to break the security of the cryptosystem. A fix for this loophole is also suggested. 
Nitin Jain, Christoffer Wittmann, Lars Lydersen, Carlos Wiechers,   Dominique Elser, Christoph Marquardt, Vadim Makarov, Ger...
quant-ph