  A multi-user quantum key distribution protocol is proposed with single
particles and the collective eavesdropping detection strategy on a star
network. By utilizing this protocol, any two users of the network can
accomplish quantum key distribution with the help of a serving center. Due to
the utilization of collective eavesdropping detection strategy, the users of
the protocol just need have the ability of performing certain unitary
operations. Furthermore, we present three fault-tolerant versions of the
proposed protocol, which can combat with the errors over different
collective-noise channels. The security of all the proposed protocols is
guaranteed by the theorems on quantum operation discrimination.
