  In this paper, we present sufficient conditions for states to have positive
distillable key rate. Exploiting the conditions, we show that the bound
entangled states given by Horodecki et al. [Phys. Rev. Lett. 94, 160502 (2005),
quant-ph/0506203] have nonzero distillable key rate, and finally exhibit a new
class of bound entangled states with positive distillable key rate, but with
negative Devetak-Winter lower bound of distillable key rate for the ccq states
of their privacy squeezed versions.
