  The local oscillator in practical continuous-variable quantum key
distribution system fluctuates at any time during the key distribution process,
which may open security loopholes for the eavesdropper to hide her
eavesdropping behaviors. Based on this, we investigate a more stealthy quantum
attack where the eavesdroppers simulates random fluctuations of local
oscillator intensity in a practical discrete-modulated continuous-variable
quantum key distribution system. Theoretical simulations show that both
communicating parties will misestimate channel parameters and overestimate the
secret key rate due to the modified attack model, even though they have
monitored the mean local oscillator intensity and shot-noise as commonly used.
Specifically, the eavesdropper's manipulation of random fluctuations in LO
intensity disturbs the parameter estimation in realistic discrete-modulated
continuous-variable quantum key distribution system, where the experimental
parameters are always used for constraints of the semidefinite program
modeling. The modified attack introduced by random fluctuations of local
oscillator can only be eliminated by monitoring the local oscillator intensity
in real time which places a higher demand on the accuracy of monitoring
technology. Moreover, similar quantum hacking will also occur in practical
local local oscillator system by manipulating the random fluctuations in pilot
intensity, which shows the strong adaptability and the important role of the
proposed attack.
