## 4 Model Proposal  
The architecture of the model proposal is complex and requires several components to ensure security, privacy, and interoperability. The first module allows stakeholders (such as patients, doctors, nurses, and administrators) to create, manage, and control their digital identities, using blockchain-based technologies to ensure immutability and security. A second module manages the storage of VCs and the keys used to exchange encrypted messages. A third module manages the interaction with IoT medical devices. A fourth module manages the issuance of VCs, such as medical reports, vaccinations, and treatments performed, storing their status and the hash of their claims on the blockchain. A fifth module manages the storage of VCs' schemas on the IPFS. Another module allows for the verification of the validity of a VC, exploiting the proofs on chain and on the IPFS. Yet another module manages the web and/or mobile application that must guarantee access to all the system functionalities, including on-chain functionalities. Through these applications, the different entities store and select the information they wish to share. In such a system, typical interactions can be the registration of stakeholders, the issuance of VCs having health data as claims, and the sharing of VCs between a patient and a doctor. So, a stakeholder, for example, a patient, creates their digital identity through an app in their smartphone and receives a public/private key with which he/she proves his/her identity and issues a VC and VP; a stakeholder, for example, a doctor or an IoT device, issues VCs containing health information and sends them to the patient, who must store them safely in his/her digital wallet; a patient shares their data with a verifier (for example, another doctor), presenting a VP through his/her wallet; and through a user-friendly web or mobile application, a verifier validates the credentials, performing a check on chain of the identity of the issuer and a check on chain and on the IPFS of the validity of the information and the VC's schema. Figure 1 shows the SSI data flow in the model proposal in which all stakeholders, such as patients and doctors and IoT medical devices, operate through their DID. In this proposal, the blockchain and IPFS represent the so-called verifiable registries. In the first registry, the DDO and VC's proofs and status are stored; on the other hand, in the second, verifiable credentials (VCs)' schemas are stored. The identity of the issuers is declared using the _identity management_ pattern with the address published on chain. Precisely these identities are stored in a register that associates their DID with their identification code in such a way that the DIDs of all the entities authorized to issue medical reports are publicly known and associated with a specific individual/organization. Figure 1: SSI data flow. All stakeholders can issue VCs. When a credential is issued, the issuer signs the credential and delivers it to the holder [4; 32], who stores it in their digital wallet. The credential issued contains all the data necessary to verify the validity of the credential. It contains the proofs which guarantee that a specific issuer has issued a given document on a specific date to a specific entity and contains the smart contract's address in which the hashes of the VC's claims are stored. So, the model proposal can guarantee the integrity of all medical reports. The combination of SSI concepts with the storage on chain of the clinical information flow of a patient allows for the exchange of reports with third parties with the certainty of data integrity and of the correct time flow since the verification of the validity of exchanged clinical reports by relying on the proofs left on chain.