  Continuous-variable (CV) quantum key distribution (QKD) employs the
quadratures of a bosonic mode to establish a secret key between two remote
parties, and this is usually achieved via a Gaussian modulation of coherent
states. The resulting secret key rate depends not only on the loss and noise in
the communication channel, but also on a series of data processing steps that
are needed for transforming shared correlations into a final string of secret
bits. Here we consider a Gaussian-modulated coherent-state protocol with
homodyne detection in the general setting of composable finite-size security.
After simulating the process of quantum communication, the output classical
data is post-processed via procedures of parameter estimation, error
correction, and privacy amplification. In particular, we analyze the high
signal-to-noise regime which requires the use of high-rate (non-binary)
low-density parity check codes. We implement all these steps in a Python-based
library that allows one to investigate and optimize the protocol parameters to
be used in practical experimental implementations of short-range CV-QKD.
