Blockchain has become popular in recent times through its data integrity and wide scope of applications. It has laid the foundation for cryptocurrencies such as Ripple, Bitcoin, Ethereum, and so on. Blockchain provides a platform for decentralization and trust in various applications such as finance, commerce, IoT, reputation systems, and healthcare. However, prevailing challenges like scalability, resilience, security and privacy are yet to be overcome. Due to rigorous regulatory constraints such as HIPAA, blockchain applications in the healthcare industry usually require more stringent authentication, interoperability, and record sharing requirements. This article presents an extensive study to showcase the significance of blockchain technology from both application and technical perspectives for healthcare domain. The article discusses the features and use-cases of blockchain in different applications along with the healthcare domain interoperability. The detailed working operation of the blockchain and the consensus algorithms are presented in the context of healthcare. An outline of the blockchain architecture, platforms, and classifications are discussed to choose the right platform for healthcare applications. The current state-of-the-art research in healthcare blockchain and available blockchain based healthcare applications are summarized. Furthermore, the challenges and future research opportunities along with the performance evaluation metrics in realizing the blockchain technology for healthcare are presented to provide insight for future research. We also layout the various security attacks on the blockchain protocol with the classifications of threat models and presented a comparative analysis of the detection and protection techniques. Techniques to enhance the security and privacy of the blockchain network is also discussed.

Abstract The emergence of smart cities and sustainable development has become a globally accepted form of urbanization. The epitome of smart city development has become possible due to the latest innovative integration of information and communication technology. Citizens of smart cities can enjoy the benefits of a smart living environment, ubiquitous connectivity, seamless access to services, intelligent decision making through smart governance, and optimized resource management. The widespread acceptance of smart cities has raised data security issues, authentication, unauthorized access, device‐level vulnerability, and sustainability. This article focuses on the holistic overview and conceptual development of smart city. Initially, the work discusses the smart city idea and fundamentals explored in various pieces of literature. Further various smart city applications along with notable implementations, are put forth to understand the quality of living standards. Finally, the article depicts a solid understanding of different security and privacy issues, including some crucial future research directions.