  Cryptocurrency is a well-developed blockchain technology application that is
currently a heated topic throughout the world. The public availability of
transaction histories offers an opportunity to analyze and compare different
cryptocurrencies. In this paper, we present a dynamic network analysis of three
representative blockchain-based cryptocurrencies: Bitcoin, Ethereum, and
Namecoin. By analyzing the accumulated network growth, we find that, unlike
most other networks, these cryptocurrency networks do not always densify over
time, and they are changing all the time with relatively low node and edge
repetition ratios. Therefore, we then construct separate networks on a monthly
basis, trace the changes of typical network characteristics (including degree
distribution, degree assortativity, clustering coefficient, and the largest
connected component) over time, and compare the three. We find that the degree
distribution of these monthly transaction networks cannot be well fitted by the
famous power-law distribution, at the same time, different currency still has
different network properties, e.g., both Bitcoin and Ethereum networks are
heavy-tailed with disassortative mixing, however, only the former can be
treated as a small world. These network properties reflect the evolutionary
characteristics and competitive power of these three cryptocurrencies and
provide a foundation for future research.
