Abstract: Core features of the blockchain technology are “de-centralization” and “de-trusting”. As a distributed ledger technology, smart contract infrastructure platform and novel distributed computing paradigm, it can effectively build programmable currency, programmable finance and programmable society, which will have a far-reaching impact on the financial and other fields, and drive a new round of technological change and application change. While blockchain technology can improve efficiency, reduce costs and enhance data security, it is still in the face of serious privacy issues which have been widely concerned by researchers. The survey first analyzes the technical characteristics of the blockchain, defines the concept of identity privacy and transaction privacy, points out the advantages and disadvantages of blockchain technology in privacy protection and introduces the attack methods in existing researches, such as transaction tracing technology and account clustering technology. And then we introduce a variety of privacy mechanisms, including malicious nodes detection and restricting access technology for the network layer, transaction mixing technology, encryption technology and limited release technology for the transaction layer, and some defense mechanisms for blockchain applications layer. In the end, we discuss the limitations of the existing technologies and envision future directions on this topic. In addition, the regulatory approach to malicious use of blockchain technology is discussed.

Key words: blockchain, privacy-preserving, peer-to-peer networking, clustering analysis, Bitcoin