  We propose a theoretical scheme for secure quantum key distribution network
following the ideas in quantum dense coding. In this scheme, the server of the
network provides the service for preparing and measuring the Bell states, and
the users encodes the states with local unitary operations. For preventing the
server from eavesdropping, we design a decoy when the particle is transmitted
between the users. It has high capacity as one particle carries two bits of
information and its efficiency for qubits approaches 100%. Moreover, it is not
necessary for the users to store the quantum states, which makes this scheme
more convenient for application than others.
