  We report the suitability of an Einstein-Podolsky-Rosen (EPR) entanglement
source for gaussian continuous-variable quantum key distribution at 1550 nm.
Our source is based on a single continuous-wave squeezed vacuum mode combined
with a vacuum mode at a balanced beam splitter. Extending a recent security
proof, we characterize the source by quantifying the extractable length of a
composable secure key from a finite number of samples under the assumption of
collective attacks. We show that distances in the order of 10 km are achievable
with this source for a reasonable sample size despite the fact that the
entanglement was generated including a vacuum mode. Our security analysis
applies to all states having an asymmetry in the field quadrature variances,
including those generated by superposition of two squeezed modes with different
squeezing strengths.

Quantum Physics