  In this paper we introduce the concept of quantum private channel within the
continuous variables framework (CVPQC) and investigate its properties. In terms
of CVPQC we naturally define a "maximally" mixed state in phase space together
with its explicit construction and show that for increasing number of
encryption operations (which sets the length of a shared key between Alice and
Bob) the encrypted state is arbitrarily close to the maximally mixed state in
the sense of the Hilbert-Schmidt distance. We bring the exact solution for the
distance dependence and give also a rough estimate of the necessary number of
bits of the shared secret key (i.e. how much classical resources are needed for
an approximate encryption of a generally unknown continuous-variable state).
The definition of the CVPQC is analyzed from the Holevo bound point of view
which determines an upper bound of information about an incoming state an
eavesdropper is able to get from his optimal measurement.
