  We consider a continuous-variable (CV) quantum key distribution (QKD)
protocol over free-space channels, which is simpler and more robust than
typical CV QKD protocols. It uses a bright laser, squeezed and modulated in the
amplitude quadrature, and self-homodyne detection. We consider a scenario,
where the line of sight is classically monitored to detect active
eavesdroppers, so that we can assume a passive eavesdropper. Under this
assumption, we analyse security of the QKD protocol in the composable
finite-size regime. Proper modulation of the squeezed laser to the shot-noise
level can completely eliminate information leakage to the eavesdropper and also
eliminate the turbulence-induced noise of the channel in the amplitude
quadrature. Under these conditions, estimation of the eavesdropper's
information is no longer required. The protocol is extremely robust to
modulation noise and highly loss-tolerant, which makes it a promising candidate
for satellite-based continuous-variable quantum communication.
