## 2 Related Work  
Regarding the literature on SSIs and healthcare, as also underlined by [PERSON] et al. [23], who, through a comprehensive systematic literature review, presented a taxonomy identifying and analyzing the open challenges in SSIs, there are not many research works in the healthcare domain. [PERSON] et al. [5] and [PERSON] et al. [7], presented an SSI management system based on Hyperledger Indy/Aries for managing all the stakeholders, including the medical devices. The former used a Hyperledger Aries blockchain to implement the model and presented a performance analysis using Hyperledger Indy to gather data. In this model, the valid data retrieval requests generated by a doctor imply the creation by the patient of a download link that allows the doctor to download necessary data. The latter presented the application MediLink, which allows patients to interface with clinics autonomously through a custom-built web and mobile application realized in ReactJS and React Native. MediLink manages six credential types, a health ID with patient demographics, insurance, a medication list including a COVID-19 vaccination status, a credit card, medical power of attorney (MPOA) for guardians of pediatric or geriatric patients, and research consent, and leverages blockchain technologies to establish the patient-centric and patient-controlled sharing of medical records across isolated institutions. Also, [PERSON] et al. [6] presented a blockchain-based architecture for the management of an SSI in the healthcare sector and validated it using the Indy/Aries architecture and the Trinsic wallet. [PERSON] et al. [8] and [PERSON] et al. [24] presented a review about SSI and blockchain technology in the healthcare sector, investigating the link between these technologies and the management of health records. [PERSON] et al. [25] discussed the applicability of blockchain-based SSI solutions and presented a use case in which a patient presents a health insurance attestation in such a way as to gain access to dental services from a doctor. An interesting white paper by the Sovrin Foundation [26], in agreement with the model proposal, presents the benefit of an SSI in the healthcare sector through some interesting use cases. Specifically, it illustrates a use case in which a 55-year-old male has Type 1 diabetes and dementia and uses a glucose meter implanted under his skin and shoe inserts that recognize him by his gait. Using an app, the male stores his glucose levels and shares these data with his endocinologist, and his parents track his physical location. In this use case, DIDcomm and peer DID connections were proposed to ensure that the glucose meter connects securely to a smartphone. Thanks to peer DIDs, unique secure identifiers known only to the meter and the smartphone are created, and no one can impersonate the male. Thanks to DIDcomm, each message exchanged is encrypted with the public key of the receiver and decrypted by the sender with his private key. Thus, the meter and smartphone exchange data securely. This use case also leverages VC concepts; a legal guardian can be appointed and, in case the male goes missing, the guardian can require the issuance of a VC to law enforcement granting access to the male's location data and his glucose meter readings for the duration of the search operation. Note that, unlike the literature articles cited above, the peculiarity of this article is that it manages not only the personal information of digital identities but also all medical reports as VCs and, to provide an in-depth understanding of the capabilities, resources and opportunities offered by a healthcare system based on an SSI and blockchain, which aims at the realization of a healthcare information system designed to integrate and decentralize all information coming from different sources, making data accessible and usable in a unified way.