  In this letter, first, we investigate the security of a continuous-variable
quantum cryptographic scheme with a postselection process against individual
beam splitting attack. It is shown that the scheme can be secure in the
presence of the transmission loss owing to the postselection. Second, we
provide a loss limit for continuous-variable quantum cryptography using
coherent states taking into account excess Gaussian noise on quadrature
distribution. Since the excess noise is reduced by the loss mechanism, a
realistic intercept-resend attack which makes a Gaussian mixture of coherent
states gives a loss limit in the presence of any excess Gaussian noise.
