  Multiparty quantum key distribution (QKD) is useful for many applications
that involve secure communication or collaboration among multiple parties.
While it can be achieved using pairwise QKD, a more efficient approach is to
achieve it using multipartite entanglement distributed over quantum networks
that connect the multiple parties. Existing studies on multipartite
entanglement distribution, however, are not designed for multiparty QKD, and
hence do not aim to maximize secret key generation rate. In this paper, we
design efficient strategies for multiparty QKD over quantum networks. For
3-party QKD, we derive closed-form expressions for analyzing key distribution
over quantum networks. We then use it to develop an efficient strategy for
3-party QKD by packing multiple stars that connect the 3 parties. For the
general form of N-party QKD, we develop an approach that packs multiple trees
to connect the N parties, while directly incorporating the estimated key rates
on network paths. Extensive evaluation of our strategies, in both grid and
random graphs, under a wide range of settings, demonstrates that our schemes
achieve high key rate, which degrades gracefully when increasing the number of
parties.
