Saturation attack on continuous-variable quantum key distribution system

Continuous-variable quantum key distribution is proven in theory secure against general attacks, but side channel is still a crucial problem for practical setup, since security proofs do not take into account all possible experimental imperfections. In this paper, we consider a loophole that links to electronics limitation of homodyne detection. By using this loophole, we propose a saturation attack combined with intercept-resend attack on the practical continuous-variable quantum key distribution using Gaussian-modulated coherent state protocol. Under this attack, Eve can launch a full intercept-resend attack and further influence the excess noise estimated by Alice and Bob. We analyse this saturation attack with operating protocol and show that our attack could render secret key without being discovered. We also propose a countermeasure against such saturation attack.