  We consider the possibilities offered by Gaussian states and operations for
two honest parties, Alice and Bob, to obtain privacy against a third
eavesdropping party, Eve. We first extend the security analysis of the protocol
proposed in M. Navascues et al., Phys. Rev. Lett. 94, 010502 (2005). Then, we
prove that a generalized version of this protocol does not allow to distill a
secret key out of bound entangled Gaussian states.
