  Healthcare blockchains provide an innovative way to store healthcare
information, execute healthcare transactions, and build trust for healthcare
data sharing and data integration in a decentralized open healthcare network
environment. Although the healthcare blockchain technology has attracted broad
interests and attention in industry, government and academia, the security and
privacy concerns remain the focus of debate when deploying blockchains for
information sharing in the healthcare sector from business operation to
research collaboration. This paper focuses on the security and privacy
requirements for medical data sharing using blockchain, and provides a
comprehensive analysis of the security and privacy risks and requirements,
accompanied by technical solution techniques and strategies. First, we discuss
the security and privacy requirements and attributes required for electronic
medical data sharing by deploying the healthcare blockchain. Second, we
categorize existing efforts into three reference blockchain usage scenarios for
electronic medical data sharing, and discuss the technologies for implementing
these security and privacy properties in the three categories of usage
scenarios for healthcare blockchain, such as anonymous signatures,
attribute-based encryption, zero-knowledge proofs, verification techniques for
smart contract security. Finally, we discuss other potential blockchain
application scenarios in healthcare sector. We conjecture that this survey will
help healthcare professionals, decision makers, and healthcare service
developers to gain technical and intuitive insights into the security and
privacy of healthcare blockchains in terms of concepts, risks, requirements,
development and deployment technologies and systems.
