## 2 Related Works
MeDShare ensures data provenance, auditing, and control for shared medical data in cloud repositories among big data entities. The system monitors entities accessing data for malicious use and records all data transitions and sharing activities in a tamper-proof manner. It employs smart contracts and an access control mechanism to effectively track data behavior and revoke access to offending entities upon detecting permission violations. Similarly, [PERSON] et al. [15] addressed the challenges of securely sharing electronic medical records (EMRs) in cloud environments, particularly concerning patient privacy and data breaches. The authors proposed a permissioned blockchain-based data-sharing framework that leverages the immutability and autonomy properties of blockchain technology to improved access control for sensitive data stored in the cloud. Their system utilizes a permissioned blockchain, granting access exclusively to invited and verified users, thus ensuring accountability by maintaining a log of all user actions. [PERSON] et al. [17] introduced a private blockchain-based system designed to streamline access management and permissions for medical data. It addresses the fragmentation and inaccessibility of medical records by enabling patients to retain control over their data while providing secure, auditable access to healthcare providers. However, MedRec faces several challenges, including scalability limitations, high transaction costs, privacy risks from metadata exposure, and the complexity of patient and provider adoption. Additionally, regulatory compliance, energy consumption due to Ethereum's Proof of Work, and integration with existing EHR systems pose significant barriers to real-world deployment. Patienttory [40] is a blockchain-based peer-to-peer network for securely storing and sharing electronic medical records (EMRs). It integrates with existing EHR systems, allowing patients and healthcare providers to access medical data while ensuring security and compliance through smart contracts and the token economy. However, the approach faces several challenges, including scalability limitations, high transaction costs, privacy risks from off-chain storage, and regulatory compliance issues, particularly with data immutability. Previous studies, reported above, have explored a wide range of blockchain-based applications in healthcare, primarily focusing on authentication, data privacy, access control, and data integrity. However, privacy risks and scalability limitations remain significant challenges, restricting the real-world applicability of these approaches. In contrast, our approach innovatively leverages blockchain technology to ensure the authenticity and integrity of event timestamps by storing only their hashes. This design choice significantly reduces blockchain costs while enhancing system maintainability, addressing a key limitation of existing research, where escalating costs hinder scalability [21]. Furthermore, our framework introduces event filtering mechanisms, allowing the selection and storage of only relevant events to optimize resource usage. It also incorporates data aggregation techniques to efficiently group multiple event records, further minimizing blockchain transaction costs. To validate its practicality, we conducted extensive experiments on real-world datasets, analyzing both transaction costs and the time required to securely store hashes on the blockchain. These strategies ensure that our solution is effective, cost-efficient, and feasible for the targeted medical domain.