  Despite tremendous theoretical and experimental progress in continuous
variable (CV) quantum key distribution (QKD), its security has not been
rigorously established for practical systems with multiple imperfections. The
idea of tagging is widely used in security proofs of discrete variable quantum
key distribution with imperfect devices. In this paper, we generalize the
tagging idea from discrete variable to continuous variable.
  Based on untagged signals, we prove the security of the imperfect quantum key
distribution system in the most conservative case. By introducing a generic
imperfection model, we can evaluate and further incorporate multiple
imperfections in the different stages such as modulation, channel and
detection. Finally, with this generic model and tagging idea, we can prove the
security of continuous variable key distribution system with multiple
imperfections. Our case study shows our proofs are able to provide secure keys
in the presence of both modulation and detection flaws.
