  In this thesis we study the finite-size analysis of two continuous-variables
quantum key distribution schemes. The first one is the one-way protocol using
Gaussian modulation of thermal states and the other is the
measurement-device-independent protocol. To do so, we adopt an efficient
channel parameter estimation method based on the assumption of the Gaussian
variables and the central limit theorem introduced by Ruppert et al. [Phys.
Rev. A 90, 062310 (2014)]. Furthermore, we present a composable security
analysis of the measurement device independent protocol for coherent attacks
with a channel parameter estimation that is not based on the central limit
theorem. We also investigated, in the asymptotic regime, an asymmetric
situation for the authenticated parties against the eavesdropper caused by
fast-fading channels. Here we assume that the eavesdropper has the full control
of the communication channel and can instantaneously change its transmissivity
in every use of it. We assumed the simple model of a uniform fading and
addressed the cases of one-way protocols, continuous-measurement
device-independent protocol in symmetric configuration and its star network
extension for three users. Finally, we extended the asymptotic study of the
one-way protocols using an arbitrary number of phase-encoded coherent states
assuming a thermal loss channel without using a Gaussian approximation.
