  One crucial step in any quantum key distribution (QKD) scheme is parameter
estimation. In a typical QKD protocol the users have to sacrifice part of their
raw data to estimate the parameters of the communication channel as, for
example, the error rate. This introduces a tradeoff between the secret key rate
and the accuracy of parameter estimation in the finite-size regime. Here we
show that continuous-variable (CV) QKD is not subject to this constraint as the
whole raw keys can be used for both parameter estimation and secret key
generation, without compromising the security. First we show that this property
holds for measurement-device independent (MDI) protocols, as a consequence of
the fact that in an MDI protocol the correlations between Alice and Bob are
post-selected by the measurement performed by an untrusted relay. This result
is then extended beyond the MDI framework by exploiting the fact that MDI
protocols can simulate device-dependent one-way QKD with arbitrarily high
precision.
