  We address the role of noisy squeezing in security and performance of
continuous-variable (CV) quantum key distribution (QKD) protocols. Squeezing
has long been recognized for its numerous advantages in CV QKD, such as
enhanced robustness against channel noise and loss, and improved secret key
rates. However, the noise of the squeezed states, that unavoidably originates
already from optical loss in the source, raises concerns about its potential
exploitation by an eavesdropper. This is particularly relevant if this noise is
pessimistically assumed untrusted. We address the allocation of untrusted noise
within a squeezed state and show that anti-squeezing noise is typically more
harmful for security of the protocols, as it potentially provides more
information to an eavesdropper. Although the anti-squeezing noise may not
directly contribute to the generated key data, it is involved in parameter
estimation and can in fact be harmful even if considered trusted. Our study
covers the effects of anti-squeezing noise in both the asymptotic and
finite-size regimes. We highlight the positive effects and limitations of
imposing trust assumption on anti-squeezing noise. Additionally, we emphasize
the detrimental impact of untrusted noise in both fiber and free-space fading
links. Our findings offer essential insights for practical implementations and
optimization of squeezed-state CV QKD protocols in realistic scenarios.
