  Quantum key distribution (QKD) can generate secure key bits between remote
users with quantum mechanics. However, the gap between the theoretical model
and practical realizations gives eavesdroppers opportunities to intercept
secret key. The most insidious attacks, known as quantum hacking, are the ones
with no significant discrepancy of the measurement results using side-channel
loopholes of QKD systems. Depicting full-time-scale characteristics of the
quantum signals, the quantum channel, and the QKD system can provide legitimate
users extra capabilities to defeat malicious attacks. For the first time, we
propose the method exploring temporal ghost imaging (TGI) scheme to perceive
quantum hacking with temporal fingerprints and experimentally verify its
validity. The scheme presents a common approach to promote QKD's practical
security from a new perspective of signals and systems.
