  Security of practical continuous-variable quantum key distribution is
addressed and a security analysis framework, which does not rely on phase-space
symmetries of signal states and correlations, is developed. In a general
purification-based approach, following optimality of Gaussian collective
attacks, it is suggested to find an equivalent generally mixed two-mode state
shared between the trusted parties and then purifying it using Bloch-Messiah
decomposition. This allows to assess security of the schemes with arbitrary
parameters, which can be typically expected in experiments. It also allows to
theoretically predict the role of asymmetries of signals and correlations on
security of the protocols. The method can be used for security analysis of
practical continuous-variable schemes directly from the measured data without
any symmetrization assumptions.
