  Cryptocurrencies gain trust in users by publicly disclosing the full creation
and transaction history. In return, the transaction history faithfully records
the whole spectrum of cryptocurrency user behaviors. This article analyzes and
summarizes the existing research on knowledge discovery in the cryptocurrency
transactions using data mining techniques. Specifically, we classify the
existing research into three aspects, i.e., transaction tracings and blockchain
address linking, the analyses of collective user behaviors, and the study of
individual user behaviors. For each aspect, we present the problems, summarize
the methodologies, and discuss major findings in the literature. Furthermore,
an enumeration of transaction data parsing and visualization tools and services
is also provided. Finally, we outline several future directions in this
research area, such as the current rapid development of Decentralized Finance
(De-Fi) and digital fiat money.
