## 3 Related Work
### Adoption of PETs in Healthcare
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Identity System** & **P-ABCs** & \begin{tabular}{c} **User Control and** \\ **Sovereignty** \\ \end{tabular} & **Security Model** & **Centralized/Decentralized** & **Drawbacks** \\ \hline \multirow{4}{*}{\begin{tabular}{c} **Identity** \\ **Mixer**[18] \\ \end{tabular} } & Utilizes zero-knowledge proofs for credential verification and privacy. & Limited selective disclosure; reliance on trusted devices for full security. & Zero-knowledge proof and blind signature. & Centralized & Complexity in usability, heavy cryptographic setup, SPoF. \\ \hline \multirow{4}{*}{**U-Prove**[17] & \begin{tabular}{c} Designed for \\ attribute-based \\ credentials with \\ partial data \\ disclosure. \\ \end{tabular} } & Provides user-side control over attributes but lacks a distributed IdP system. & Signature-based system. & Centralized & High implementation complexity, limited adoption, SPoF. \\ \hline \multirow{4}{*}{\begin{tabular}{c} **ABC4 Trust** \\ **ABC4 Trust** \\ **[20]** \\ \end{tabular} } & Privacy via p-ABC and and data & User-controlled attributes with & Combines zero-knowledge proofs & Centralized & SPoF, usability challenges. \\  & minimization; supports selective & potential for & \begin{tabular}{c} zero-knowledge proofs \\ and anonymous \\ credentials. \\ \end{tabular} & Centralized & \begin{tabular}{c} SPoF, usability \\ challenges. \\ \end{tabular} \\  & disclosure. & \begin{tabular}{c} Strong user \\ sovereign with \\ decentralized \\ issuance; however, \\ ldPs may pose \\ privacy risks. \\ \end{tabular} & Strong user & & & & \begin{tabular}{c} The level of privacy \\ heavily relies on the \\ segregation of \\ components and the \\ trustworthiness of their \\ implementations, SPoF, \\ complex authorization \\ processes, PKI, tracking \\ issues. \\ \end{tabular} \\ \hline \multirow{4}{*}{\begin{tabular}{c} **ARIES**[21] \\ **ARIES**[21] \\ **ARIES**[21] \\ **privacy-preserving** \\ **credentials.** \\ \end{tabular} } & \begin{tabular}{c} Blockschain-based \\ self-sovereign ID, \\ emphasizing \\ decentralized trust; \\ builds a platform for \\ intermediaries \\ between users and its \\ network, and an \\ interface for other \\ identity systems is \\ also supported. \\ \end{tabular} & \
\begin{tabular}{c} Anonymous credentials \\ based on \\ zero-knowledge proofs \\ guarantee the principle \\ of \"least amount of \\ identifying \\ information\" \\ disclosure; only \\ authorized parties and \\ agencies can access the \\ attributes; supports \\ omnidirectional \\ \end{tabular} & Decentralized & Public blockchain visibility can impact sensitive data privacy, \\  & & & &
\begin{tabular}{c} SPoF, \\ not clear about the \\ usability and user \\ understanding of \\ privacy in Sovrin. \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Differences in privacy, user autonomy, and technical structures across identity management systems. We believe that blockchain technology can be effectively utilized for identity management purposes, such as authentication and access control, while not being used for storing healthcare information. There are works in the literature that use blockchain for storing and managing healthcare data [34]. Additionally, e-health organizations often support a range of diverse and transparent e-services, which requires the integration of various systems [35]. These factors, along with technical limitations, such as block size restrictions [36], the immutable and public nature of blockchain [37], and the lack of technical expertise and resources within many healthcare institutions, make blockchain integration a challenging task. As a result, our solution avoids the direct storage of health records on the blockchain. Instead, our system ensures that sensitive data remains off-chain and securely protected using cryptographic techniques such as zero-knowledge proofs (ZKPs) and homomorphic encryption. These technologies enable controlled data sharing while safeguarding the privacy of sensitive health information.