  We show that partially trusting the phase noise associated with estimation
uncertainty in a LLO CVQKD system allows one to exchange higher secure key
rates than in the case of untrusted phase noise. However, this opens a security
loophole through the manipulation of the reference pulse amplitude. We label
this as "reference pulse attack" which is applicable to all LLO-CVQKD systems
if the phase noise is trusted. We show that, at the optimal reference pulse
intensity level, Eve achieves unity attack efficiency at 23.8km and 32.0km
while using lossless and 0.14dB/km loss channels, respectively, for her attack.
However, in order to maintain the performance enhancement from partially
trusting the phase noise, countermeasures have been proposed. As a result, the
LLO-CVQKD system with partially trusted phase noise owns a superior key rate at
20km by an order 9.5, and extended transmission distance by 45%, than that of
the phase noise untrusted system.
