  Quantum digital signatures (QDS), which utilize correlated bit strings among
sender and recipients, guarantee the authenticity, integrity and
non-repudiation of classical messages based on quantum laws.
Continuous-variable (CV) quantum protocol with heterodyne and homodyne
measurement has obvious advantages of low-cost implementation and easy
wavelength division multiplexing. However, security analyses in previous
researches are limited to the proof against collective attacks in finite-size
scenarios. Moreover, existing multi-bit CV QDS schemes have primarily focused
on adapting single-bit protocols for simplicity of security proof, often
sacrificing signature efficiency. Here, we introduce a CV QDS protocol designed
to withstand general coherent attacks through the use of a cutting-edge
fidelity test function, while achieving high signature efficiency by employing
a refined one-time universal hashing signing technique. Our protocol is proved
to be robust against finite-size effects and excess noise in quantum channels.
In simulation, results demonstrate a significant reduction of over 6 orders of
magnitude in signature length for a megabit message signing task compared to
existing CV QDS protocols and this advantage expands as the message size grows.
Our work offers a solution with enhanced security and efficiency, paving the
way for large-scale deployment of CV QDS in future quantum networks.
