  With the advancement of quantum computing, the security of public key
cryptography is under serious threat. To guarantee security in the quantum era,
Quantum Key Distribution has become a competitive solution. QKD networks can be
classified into measurement-device-dependent network and
measurement-device-independent network. In measurement-device-dependent
networks, the information is available for all trusted relays. This means that
all trusted relays are strongly trusted relays that require strict control,
which is difficult to realize. To address this issue,
measurement-device-independent networks reduce the proportion of strongly
trusted relay nodes by introducing untrusted relays. However, due to the higher
key rate of measurement-device-dependent protocols over short distances, the
communication capability of measurement-device-independent networks has a
degradation compared to measurement-device-dependent networks. Therefore, how
to reduce the dependence of QKD networks on strong trusted relays without
significantly affecting the communication capability has become a major issue
in the practicalization process of QKD networks. To address this issue, a novel
Multi-Protocol Collaborative networking cell is proposed in this paper. The QKD
network built by the MPC networking cell reduces the dependence on strongly
trusted relays by combining the two protocols to introduce weak trusted relays
while maintaining the high communication capacity. What's more, to further
enhance the overall performance of the QKD network, an optimal topology design
method is presented via the proposed flow-based mathematical model and
optimization method. The simulation results show that the proposed scheme
reduces the dependence on strongly trusted relays without a significant
reduction in communication capability, our work holds great significance in
promoting the practicalization of QKD networks.
