Bawany et al. [12] conducted an in-depth analysis of the potential benefits and adaptability challenges associated with integrating blockchain technology into the telehealth sector. Their research aims to develop a comprehensive telehealth framework called BlockHeal that integrates essential healthcare services using Blockchain to ensure privacy, security, and trust. By leveraging smart contracts, BlockHeal includes decentralized storage, secure data exchange, and various services like digital prescriptions, drug supply chain management, health insurance, and emergency services. Furthermore, Zhuang et al. [13] presented a thorough analysis of the significant enhancements that Blockchain brings to the exchange of healthcare data. They use Blockchain and smart contracts to ensure data security and data provenance and provide patients with control over their health records. They demonstrate the feasibility, stability, security, and robustness of the proposed model through a large-scale simulation, highlighting its potential to improve patient-centric data exchange. Furthermore, Sheela et al. [14] examined the significant effect of blockchain technology on the healthcare sector, especially regarding security and privacy. Their outcomes suggest that Blockchain can significantly improve data integrity by guaranteeing that health records remain accurate and unaltered. This technology ensures nonrepudiation, meaning when data is recorded, it cannot be denied, hence increasing trust in the system. At this level, Puneeth et al. [15] proposed a blockchain-based framework to secure Electronic Health Records (EHR) with patient-centric access control using smart contracts, integrating Blockchain’s immutability and decentralization features with advanced cryptographic techniques. The framework uses a hybrid cryptographic algorithm for encryption and stores EHR data using off-chain storage known as InterPlanetary File System (IPFS). Furthermore, Boumezbeur et al. [16] proposed a blockchain-based framework for secure EHR sharing. The framework uses cryptographic techniques and smart contracts to manage access control and ensure data privacy. The framework shows efficient encryption and decryption times. It also ensures flexible access control by allowing patients to manage access to their health records. Nevertheless, the process for revoking access permissions might not be straightforward, potentially leading to unauthorized access if permissions are not updated. In addition, Tahir et al. [17] proposed a privacy-preserving and secure framework for sharing Electronic Health Records (EHRs) using blockchain technology. The framework leverages cryptographic techniques and smart contracts on the Ethereum blockchain to ensure secure storage and access control of EHRs. The system architecture includes three layers: data collecting, data storing, and data sharing, involving entities such as EHR owners, EHR users, cloud storage, and Blockchain. The framework aims to enhance data privacy, authenticity, integrity, confidentiality, flexible access control, and user authentication. However, the framework presents some limitations: access to data with unlimited time, automated user authentication without control from a legitimate authority, and no option to revoke authentication. Moreover, Shah et al. [18] proposed an e-healthcare management system using the Internet of Things (IoT) and blockchain technologies. This aims to provide comprehensive, reliable, and secure services for patients. It also tries to address the challenges of providing low-cost and high-quality medical services, especially in the context of global aging. However, as patients store EHR data in the system, there is a risk of data loss, which challenges data integrity. Further, Li et al. [19] proposed a secure data-sharing system for electronic health (eHealth) systems. The framework, named TrustHealth, leverages blockchain technology and Trusted Execution Environments (TEEs) to improve eHealth security by ensuring data privacy, authenticity, integrity, and confidentiality. While it provides robust user authentication and access control through smart contracts and cryptographic techniques, it faces challenges such as the complexity of key management and potential vulnerabilities in smart contract design. Moreover, Mao et al. [20] presented a blockchain-based platform designed to enhance the management and sharing of medical data. The platform aims to address the challenges of data authenticity, security, and traceability in the medical field. Smart contracts are used for trusted storage and data authenticity verification. They manage user access control with predefined rules. Although the paper emphasizes data security, it could benefit from the integration of advanced privacy-preserving techniques, such as homomorphic encryption or differential privacy.

Furthermore, numerous studies have explored the integration of blockchain technology with the Internet of Things (IoT) [21–25]. While these works highlight significant advancements and potential applications, they also reveal several limitations in terms of access control management, user authentication, data authenticity, and data ownership.

Furthermore, numerous research efforts have been undertaken to mitigate and address security and privacy-related issues within an Internet of Things environment through the application of blockchain technology, often referred to as Blockchain 4.0. For instance, Hameed et al. [26] present a comprehensive taxonomy of privacy and security requirements specifically adapted to Blockchain-based Industry 4.0 applications. They categorize these requirements into three distinct types: first, Confidentiality, Integrity, and Availability Triad. This one focuses on ensuring that data is kept confidential, remains unaltered, and is accessible when needed. Second, the Authentication, Authorization, and Accounting Triad is crucial for verifying the identities of users (authentication), determining their access rights (authorization), and keeping track of their activities (accounting). Third, securing smart contracts involves ensuring that they are free from vulnerabilities, function as intended, and cannot be tampered with. The integration of blockchain technology in IoT environments, as outlined in these categories, aims to create a more secure and trustworthy system. By addressing the CIA and AAA triads, along with securing smart contracts, Blockchain can significantly enhance the security and privacy of IoT applications. This approach not only protects data and ensures its integrity but also provides a transparent and accountable framework for managing access and interactions within the IoT ecosystem. Furthermore, our system will consider the above requirements to mitigate the aforementioned limitations in the literature. By incorporating advanced security measures, ensuring compliance with GDPR regulations, and leveraging Blockchain, we aim to enhance the privacy and security of patient data.

This paper proposes an access management system that leverages blockchain technology. It aims to improve patient privacy and secure data within the telehealth and telemedicine sectors. The system seeks to record every single access to data in Blockchain, thereby providing patients with full control over their data and increased transparency regarding data sharing. With the General Data Protection Regulation (GDPR) in mind, this study aims to establish a patient-oriented system for access management. Moreover, the potential contributions of blockchain technology to the telehealth and telemedicine sectors motivate its application for dynamic access management. The characteristics of blockchain technology mitigate challenges in the existing systems. This suggested approach employs smart contracts for automating activities such as controlling access, identifying unallowed use, and adding or removing nodes from the system network based on their trustworthiness. The following section outlines the key enhancements that blockchain technology brings to our system:

Security. Blockchain can guarantee patient data confidentiality and integrity, it also offers authenticity to data requestors.

To ensure that our system solves the privacy and security issues, we proceed an evaluation process using formal security modeling framework (SeMF) [27], which is based on formal language theory. SeMF aims to validate the usability of our system to effectively address privacy and security issues. Moreover, SeMF stands for two main processes the formalization and the validation of the system’s privacy and security properties.

Consequently, our work aims to provide two substantial contributions to the improvement of patient security and privacy, as follows:

1. This involves defining the proposed patient-centric access mechanism that satisfies the GDPR regulations and our security requirements, detailing the system’s design and architecture, outlining all potential actions related to access management, and describing the proposed smart contracts, including their design goals.

2. This involves the formalization and validation of the system’s privacy and security properties by applying the formal security modeling framework SeMF, performing the cost analysis, and comparing it with existing solutions.

Ensuring security is a fundamental aspect of our system, as it is paramount for establishing and maintaining trustworthiness in the system. According to [26], the security requirements can be outlined here:

Confidentiality. This is the key security requirement of any application or system designed to protect patient data Di from unauthorized access or potentially malicious users. In other respects, there is a potential risk of compromising patient privacy. Di may include identifiers, which are considered as sensitive information.

In the upcoming section, the SeMF will formalize these security requirements in detail.

To ensure compliance with the General Data Protection Regulation [6], our proposed system must satisfy the following access management requirements:

Unambiguous. Access must be granted through clear and affirmative action to prevent any ambiguity.

Transparency is a fundamental requirement for any system designed to ensure lawful actions and prevent non declared activities that could compromise patient privacy. It is imperative that patients are informed about all actions related to the access of their data once they have granted permission to healthcare providers (Ri). To ensure transparency, the system permanently records every activity, making it accessible at any time.

The blockchain built-in features record all performed actions A1, …, An in an immutable ledger and make them viewable and auditable to all authentic users P. Therefore, this feature makes the system more reliable and transparent to all acting users. Moreover, the users will be more informed about what happens in the system based on their own local. In addition, Table 3 summarizes all the possible access-related actions A1, …, An. Hence, all these actions can be formalized as it consists of three main parts: Action, Entity (Ui, Ri), and Parameters.

This section covers the suggested smart contract SCi, which initially consists of verifying the data requestor’s authenticity and the legitimacy of the accessing activities. Additionally, it is for the purpose of automatically switching access status based on a withdrawal decision made by the patient or expiration of the defined period of time t. Furthermore, it is used to transfer measured data Di to decentralized storage. The system design includes the following four smart contracts to accomplish this objective:

Smart Contract 1 (SC1). It first verifies the identity of users, particularly healthcare providers (Ri). Additionally, the Regulatory Authority (e.g., the Healthcare Ministry) acts as the smart contract owner. The RA has the ability to add new users or ban existing ones. The output is recorded in the Blockchain to identify the trusted and banned users. Therefore, based on the SC1 property that provides trustworthiness and authenticity to users, the design goal can be formalized as follows:

Design Goal 1. It is authentic for Ui that actions Ai...An are performed by authentic and trustful users (Authentication).

Smart Contract 2 (SC2). It takes the data hash, the date and time of data measurement, and other relevant details as input parameters. The output is stored in the Blockchain. Then, the measured data is stored off-chain. As a result, the data’s authenticity is verified through blockchain. Therefore, the design goal can be formalized as follows:

Design Goal 2. It is authentic for Ui that the measured data by the wearable health-based devices remain the same when transferred to the decentralized storage (Data integrity).

Design Goal 3. It must be authentic for Ri that the received data is the data that Ui transferred to the decentralized storage and was measured using Ui’s health-based devices (Data authenticity).

Smart Contract 3 (SC3). It allows healthcare providers to request permission to access data. Additionally, it enables patients Ui to grant access by setting a time limit t or to revoke/withdraw current access to ReFi. The smart contract SC3 can automatically revoke access once the specified period t has expired. Therefore, access will be unlawful. Once the healthcare provider requests access, SC3 triggers SC1 to ensure that Ri is not a banned user, and then Ui receives the request. The output is stored in the Blockchain. Therefore, the design goal is as follows.

Design Goal 4. Each granted access is authentic for all users ∈ P, and remains valid until t is expired or Ui revokes access ReFi (Access authenticity).

Smart Contract (SC4). It checks the validity of accessing Di by Ri based on access ReFi. It enables the system to detect unlawful access. SC4 is triggered, once Ri initiates an action Ai to access data. SC4 takes SC1’s output as an input, and the access ReFi.

Design Goal 5. It must be authentic for Ui that Ri can access data uniquely based upon the access ReFi (Data confidentiality).

Note: Ri is authenticated by the Regulatory Authority (RA), once joining the system. Hence, Ri can perform transactions by sending access request through blockchain account to user Ui (Patient) who is the owner of data Di. Further, Ui receives access request and sends back access decision (Grant/Revoke) to data requestor Ri via blockchain account.

The sequence diagram provided in Fig. 3 highlights the step-by-step access request process. In addition, before Ri performs any transaction, SC1 is automatically executed to report if Ri is a trusted or banned user. If Ri is banned, action Ai becomes invalid. On the other hand, if Ri is a trusted user, action Ai becomes valid, and Ri is allowed to request access such as follows:

Step 1.1: Healthcare provider Ri performs and signs a transaction (Ai action or a set of actions A1…An) through blockchain account to request access to Ui’s data Di or start measuring new data Di. The transaction contains many input parameters, such as Pi purpose to access Di, data type, Ni nature (Old or new data Di), and time t required to access data.

Furthermore, following to Step 3.3, Fig. 4 illustrates the process by which the validity of accessing data is checked according to patient Ui’s decision (Grant/Revoke). SC4 ensures the enrolment of this process. As a result, it satisfies DG5.

Step 4.1: Once Ri receives the Ui’s decision with valid access ReFi, Ri can access measured data Di or measure new data using Ui’s devices for a predefined period of time t. Furthermore, Ui is informed of all access activities, with sufficient details of what actions performed by Ri.

Note: Ri can only access newly measured data Di until it is stored in the decentralized storage database.

Steps 4.2 and 4.3: Once Ri performs a transaction, Ai through the network in order to access Di. Ui receives an access report to their blockchain account.

In addition, according to GDPR, Patient Ui is able to revoke/withdraw granted access ReFi at any time. Then, Ri will automatically get notified of the patient’s new decision following the steps below:

Step 1.1 Revoke: Ui revokes the granted access ReFi to Ri.

This section discusses the trustworthiness of the system through the trust assumptions made based on blockchain technology properties, which can be utilized for the formalization and validation of the system’s security properties by applying the security modeling framework SeMF. Further, the term trustworthiness expresses the degree to which a particular trust assumption is achieved through the system properties [26]. As discussed earlier, the system design includes three main users P: Ui, Ri, and RA, with a unique local view λ by which users interact with the system. Further, the patient is the data Di owner and can share their health-related data with only trusted users Ri. For example, the patient has full trust in the system’s properties, their data Di cannot be shared with unreliable users, and the patient is able to revoke access at any time. Hence, the system’s trustworthiness proves the authenticity of all access-related actions that are performed by an authentic user, and all access-related data is permanently stored. To this end, the built-in blockchain features can contribute effectively to ensure our system’s trustworthiness. These features include authenticity, integrity, availability, nonrepudiation, ledger immutability, auditability, etc. Therefore, Blockchain provides an immutable and transparent record of all access-related transactions that occur. Hence, it ensures trust in results shown to the users even after a series of actions ω.

However, in a public blockchain, all data and transactions that are recorded within blocks can be visible to all nodes in the network, which presents some privacy issues. As a result, health-related data or any sensitive data cannot be recorded in the ledger. This issue was addressed in the proposed system, to store all health-related data or other sensitive data in a decentralized storage database such as IPFS [11] in an encrypted form with the use of encryption methods such as the homomorphic encryption approach [30] or Advanced Encryption Standard same as implemented in [31]. Furthermore, other ways of storage can be explored such as introduced in [32] Blockchain-based medical health record access control scheme with efficient protection mechanism and patient control. That relies on a server cloud with the use of a proxy re-encryption scheme to enhance data security. In our system, only access-related transactions are stored in the ledger. Further, to strengthen the security of the system, RA, by means of SC1, works as the first security layer to add only trusted nodes and ban untrusted ones.

Moreover, the key characteristics of Blockchain especially those based on cryptography can contribute positively to enhance the system’s security and ensure privacy. The trust assumptions relaying on Blockchain’s security properties.

Trust assumption 1. All received actions A1…An from Blockchain are whether previously performed and signed by authentic users P or by triggered SCi once a set of conditions are met (Authenticity/Digital signature/Smart contract).

Trust assumption 2. All added actions A1…An to the chain must be authentic (Authenticity).

Trust assumption 3. Any measured data by the wearable health-based devices remains the same when transferred to the decentralized storage. It is achieved by the mean of hash value stored in the Blockchain (Data Integrity).

Trust assumption 4. Any transaction-related data shown on the user’s blockchain account must be previously transferred to Blockchain and signed by an authentic user or a smart contract (Authenticity/Digital signature).

Trust assumption 5. Once a user ∈ P performs a transaction and sends it through the network, the transaction-related data remains unchangeable once added to the chain within a new block (Authenticity/Integrity).

Trust assumption 6. SCi can be automatically executed once certain conditions are met (Automation/Smart contract).

Trust assumption 7. All performed A1…An are timestamped and permanently added to a chain within a block following a certain order. The block is validated and linked to the last block in the chain by the mean of a consensus algorithm (Timestamp/Order proof).

Trust assumption 8. Every node in the network keeps a copy of the whole ledger (Distribution/Immutability/Proof of evidence).

The purpose of authentication is to verify users’ identities within the system and to guarantee that actions A1, …, An are authentic. The authentication property is formalized and validated using the following two definitions:

1-A set of actions Γ ⊆ ∑ is authentic for P ∈ ℙ after a sequence of actions ω ∈ B with respect to WP if alph(x) ∩ Γ = ∅ for all x ∈ λ − 1 P (λP(ω)) ∩ WP.

2-For a system S with behaviour B ⊆ ∑∗, user P ⊆ ℙ, and actions a, b ∈ 6, auth(a, b, P) holds in B if for all ω ∈ B, whenever b ∈ alph(ω), the action a is authentic for P.

To formalize and validate the proof of authenticity in order to prove the system’s authorization, nonrepudiation, and integrity properties. The SeMF’s Definition 3 is used as follows:

Definition 3 (Proof of authenticity). For a system S with behavior B ⊆ Σ∗ and actions a, b ∈ Σ, precede(a, b) holds in S if for all ω ∈ B with b ∈ alph(ω), it follows that a ∈ alph(ω).

Proposition 3. If user2 performs the action Receive, user2 must have access to proof in order to show other users that the matching sent action Send occurred prior to the received action Receive.

Blockchain functions as a proof of evidence, by ensuring that all associated data and transactions are permanently recorded in a distributed ledger. Due to its design, Blockchain is immutable and cannot be altered without affecting all subsequent blocks in the network. It offers also timestamped records. These inherent features of Blockchain, such as immutability and nonrepudiation, enable us to leverage assumptions 7 and 8 for proof of authenticity.

Proof of Proposition 3. Proposition 3 is validated the same way as Proposition 1 was validated. Hence, the aforementioned assumptions 7 and 8 are best describing user2’s initial knowledge W2.

User2 can retrieve the recorded transaction-related data associated with the action Receive after receiving the action (Trust assumption 8).

Consequently, the properties of nonrepudiation, integrity, and authority are proven by formalizing and verifying the proof of authenticity.

In our implementation, we used the Ethereum development tool Remix IDE. Additionally, smart contracts code is written in the Ethereum programming language Solidity. The smart contracts code has passed the security analysis with the help of Remix IDE built-in security tool and Mythril tool. In our testing case, we consider that all system participants have their own Ethereum addresses, and the smart contracts are deployed and owned by the Regularity Authority. The performance was tested on the Sepolia testnet, which has an average transaction time of 13 s. The following table summarizes the gas consumption of each function call. Thus, the experimental results have demonstrated the efficiency of the system in terms of time and cost savings, as shown in Table 4.

Having established the necessity of employing SC3 and SC4 based on the formal definition of SeMF, including authentication, the following section delves into the compliance of our proposed solution with the General Data Protection Regulation (GDPR) as outlined in Section 5. By using SC3 and SC4, we ensure that our system meets the standards of the GDPR. This compliance is crucial for establishing trust and confidence among users.

In the following subsections, we will explore in detail how our system adheres to GDPR regulations of data protection and privacy:

Unambiguous: By eliminating any ambiguity regarding the period of access SC3 guarantees that access is granted for a specified duration t. This precise time-bound access control is crucial for maintaining data security and user trust.

Table 5 highlights a comparison of our system with existing solutions. All systems, including ours, support patient-centric access control. In addition, only reference [16] and our system provides authentication. All systems claim to ensure data integrity, but reference [18] notes a risk when patients are involved in the data upload process. Thus, our system ensures data integrity. All systems, including ours, ensure data authenticity. Further, solutions [15–18] have conditional access authenticity, with access granted for an unlimited period and revoked by the patient. Our system grants access for a limited period, with the patient able to revoke access before the period ends. All systems, including ours, ensure data confidentiality. Only reference [16] and our system are GDPR compliant.