## 5 A User-Centric Perspective for the Internet of Medical Things  
From the analysis we did in the previous section, we saw that the majority of research papers prefer to use Permissioned solutions instead of permissionless ones. This interesting fact is probably related to the opportunity represented by a permissioned and private model that offers a more flexible ledger in terms of authority. The reason to implement this model is mainly related to the possibility of keeping control of the Blockchain by a restricted number of participants, usually referred to as a consortium. However, this model is risky and it sacrifices decentralization and immutability: the consortium could have the concrete potential to modify the ledger. This consideration is particularly important for those implementations that try to reach user-centricity because if a ledger could be changed by a restricted group of participants (without considering tampering), it could not be defined as a user-centric system. Thus, this problem posed some questions to researchers that probably encouraged the introduction of decentralized storages combined with Blockchain (as IPFS) not only for scalability reasons but also for security because they constitute two different technologies. A user-centric system is a system where users have more control and flexibility with respect to ordinary systems. In the healthcare domain, this means that patients could be able to manage and own their data entirely, making it live in their personal devices or their preferred locations. In this section, we will assess three more things out of the type of Blockchain for what concerns implementations: if the consensus is decentralized or restricted to a limited number of participants, if they mentioned user-centricity and which of them is finally user-centric. In order to classify the implementations, we considered the type of DLTs, the consensus and so, the strength of the solution proposed in terms of user-centricity which is the ability of the user to control its data. Results are shown in Table 5 and, in this section, we are going to discuss each paper. [PERSON] et al. [38] propose a platform named BlockHE, based on Blockchain, for data sharing between individuals employing two Blockchains: EMR-Chain, for medical institutions; PHD-Chain, for individuals. Both institutions and individuals can submit and share healthcare data. They handle healthcare data through the combination of off-chain storage and on-chain transactions. The off-chain storage is achieved by storing the data in the distributed databases of the hospitals while the on-chain verification is achieved by including the hash value of each medical record in the transaction. Because medical institutions usually submit very privacy-sensitive data as medical reports and treatments (because of healthcare professionals) while individuals are more prone to submit a massive amount of data (because of data generated by IoMT devices), such kind of approach provides from one side a centralized solution where institutions can keep control over user data and to the other side a decentralized solution for data provenance. The whole system could not be considered user-centric but could solve the problem of data management in a healthcare environment. [PERSON] et al. [39] propose Healthchain, a large-scale health data management scheme based on Blockchain where users have full control of their data as well as access policies. The system uses two Blockchains, namely Userchain, a public Blockchain used to publish users' data, and Doccchain, a private Blockchain of healthcare institutions used to publish doctors diagnoses. For the researchers, this scheme should ensure the design goals of supporting large-scale IoT devices, reaching a high efficiency, and creating a real-time online diagnosis system, which could preserve privacy, ensure accountability and, finally, manage permissions.