  In this brief, we conduct a complex-network analysis of the Bitcoin
transaction network. In particular, we design a new sampling method, namely
random walk with flying-back (RWFB), to conduct effective data sampling. We
then conduct a comprehensive analysis of the Bitcoin network in terms of the
degree distribution, clustering coefficient, the shortest-path length,
connected component, centrality, assortativity, and the rich-club coefficient.
We obtain several important observations including the small-world phenomenon,
multi-center status, preferential attachment, and non-rich-club effect of the
current network. This work brings up an in-depth understanding of the current
Bitcoin blockchain network and offers implications for future directions in
malicious activity and fraud detection in cryptocurrency blockchain networks.
