  Based on quantum encryption, we present a new idea for quantum public-key
cryptography (QPKC) and construct a whole theoretical framework of a QPKC
system. We show that the quantum-mechanical nature renders it feasible and
reasonable to use symmetric keys in such a scheme, which is quite different
from that in conventional public-key cryptography. The security of our scheme
is analyzed and some features are discussed. Furthermore, the state-estimation
attack to a prior QPKC scheme is demonstrated.
