We address the security of continuous-variable quantum key distribution with
squeezed states upon realistic conditions of noisy and lossy environment and
limited reconciliation efficiency. Considering the generalized preparation
scheme and clearly distinguishing between classical and quantum resources, we
investigate the effect of finite squeezing on the tolerance of the protocol to
untrusted channel noise. For a long-distance strongly attenuating channel and
the consequent low reconciliation efficiency, we show that feasible limited
squeezing is surprisingly sufficient to provide the security of Gaussian
quantum key distribution in the presence of untrusted noise. We explain the
effect by behaviour of the Holevo quantity, which describes the information
leakage, and is effectively minimized by the squeezed states.Comment: 14 pages, 7 figure