# Security, Privacy, and Reliability in Digital Healthcare Systems Using Blockchain
## 2 Literature Review  
The tremendous growth in the number of IoT devices and their impacts on social life have created a protected, open, and unique environment in which patient health records can be securely accessed. The models for IoT necessitate the utilization of a central cloud server, which results in a single point of failure (SPOF) [12]. In order to provide solutions to such problems for sensor-based medical devices, blockchain is considered as one of the best tools and platforms for a decentralized environment. The innovation of blockchain is a huge advancement in the IoT security field [12]. The applications of blockchain technology start from its decentralization, trust, and distributed nature from diverse points of view. The use of blockchain with IoT devices provides more a secure environment that is not dependent on a single trusting authority. During the development of IoT frameworks, there are more possibilities to have an expanded number of cooperating gadgets or things in them. These expanded numbers of gadgets attempt to communicate with each other by using Internet as a medium. This would result in numerous obstacles because most of the gathered data are kept in the focal servers of IoT systems. Therefore, in the literature, researchers have tried to cope with these issues. [PERSON] et al. [1] proposed a system based on a patient monitoring system and an interference-aware system for the IoT. The authors also provided a comparative analysis with the benchmark models and traditional central-authority-dependent models, which rely on a central authority node. The authors also proposed a lightweight ring-signature-based consensus algorithm for a sensor-based blockchain network. [PERSON] et al. also proposed the idea of a decentralized medical-data-sharing scheme for cross-domain use with the Hyperledger Fabric platform. The authors provided many details about the application of this blockchain tool in an IoT-based environment and peer-to-peer networks. They also designed a P2P-based record-sharing protocol that supports smart-contract-based access control polices. The authors of [13] highlighted recent issues and developed an access control policy for digital medical records through a fine-grained access control system. A novel architecture was designed by authors in the literature to secure electronic healthcare records based on a distributed ledger technology and also improved the interoperability of health records between different organizations [14]. However, the authors also provided a performance evaluation by using a blockchain tool and proposed some endorsement policies. In [15], the authors explored the performance metrics of the Hyperledger Fabric framework. Some researchers provided optimization of security and performance by using a blockchain platform with sensor-based networks. The authors of these research works provided a complete justification for enhanced performance with minimal computation time. Last but not least, the authors of [16] devised a searchable encryption scheme for electronic healthcare records using blockchain. They designed an algorithm for indexing healthcare records and a two-part evaluation scheme. [PERSON] et al. [14] proposed a peer-to-peer network in order to improve privacy and security when connecting remote medical sensors and devices. The authors designed a framework of modified blockchain models while considering IoT sensor devices. In summary, the contributions of the authors were the resolution of the issues of using a blockchainwith sensors. [PERSON] et al. [17] designed a method for using a blockchain in a doctor-and-patient setup and for booking for patients. [PERSON] et al. [3] proposed a modified blockchain based on directed acyclic graphs, which were proposed by [PERSON] and [PERSON] [18]. However, the transaction protocol was for a private blockchain, and the author also provided a comparative analysis between private and public blockchains.