To date, bitcoin has been the most successful application of blockchain technology and has received considerable attention from both industry and academia. Bitcoin is an electronic payment system based on cryptography rather than on credit. Regardless of whether people are in the same city or country, bitcoin can be sent by any one person to any other person when they reach an agreement. The market value of bitcoin has been rising since its advent in 2009, and its current market value is US160 billion. Since its development, bitcoin itself has exposed many problems and is facing challenges from all the sectors of society; therefore, adversaries may use bitcoin’s weakness to make considerable profits. This survey presents an overview and detailed investigation of data security and privacy in bitcoin system. We examine the studies in the literature/Web in two categories: 1) analyses of the attacks to the privacy, availability, and consistency of bitcoin data and 2) summaries of the countermeasures for bitcoin data security. Based on the literature/Web, we list and describe the research methods and results for the two categories. We compare the performance of these methods and illustrate the relationship between the performance and the methods. Moreover, we present several important open research directions to identify the follow-up studies in this area.

With the development of network technology and cloud computing, data sharing is becoming increasingly popular, and many scholars have conducted in-depth research to promote its flourish. As the scale of data sharing expands, its privacy protection has become a hot issue in research. Moreover, in data sharing, the data is usually maintained in multiple parties, which brings new challenges to protect the privacy of these multi-party data. In this paper, we propose a trusted data sharing scheme using blockchain. We use blockchain to prevent the shared data from being tampered, and use the Paillier cryptosystem to realize the confidentiality of the shared data. In the proposed scheme, the shared data can be traded, and the transaction information is protected by using the (p, t)-threshold Paillier cryptosystem. We conduct experiments in cloud storage scenarios and the experimental results demonstrate the efficiency and effectiveness of the proposed scheme.