Security of quantum key distribution protocols using two-way classical   communication or weak coherent pulses
  We apply the techniques introduced in [Kraus et. al., Phys. Rev. Lett. 95, 080501, 2005] to prove security of quantum key distribution (QKD) schemes using two-way classical post-processing as well as QKD schemes based on weak coherent pulses instead of single-photon pulses. As a result, we obtain improved bounds on the secret-key rate of these schemes. 
Barbara Kraus, Cyril Branciard, and Renato Renner