With the continuous development of society, the demand for international travel, academic exchanges, and medical tourism has increased significantly. However, inconsistencies in healthcare regulations across countries have led to challenges in verifying travelers’ health status. In recent years, fraudulent health passports [1] and medical data breaches have emerged as serious threats to public health and data privacy. For example, in 2021, Europol reported the dismantling of multiple fraudulent COVID-19 vaccine passport networks operating across Europe, where counterfeit certificates were sold on the black market to bypass travel restrictions. Similarly, in 2022, a massive healthcare data breach in the United States exposed sensitive patient records, affecting over 10 million individuals. These incidents highlight the vulnerabilities in current digital health documentation and the risks associated with central storage architectures, which are susceptible to cyberattacks and unauthorized data access [2]. Traditional paper-based health passports are prone to forgery, and digital records suffer from data silos and privacy issues. To address these challenges, we propose a blockchain-based health passport system integrating on-chain and off-chain storage, searchable encryption, and an optimized consensus mechanism for enhanced security, privacy, and efficiency.

However, there are huge differences in disease prevention measures and requirements in different countries and regions, resulting in differences in entry and exit health standards. In this context, many countries and regions have formulated strict Healthcare and machine learning policies to ensure public health and safety [3,4]. In this context, personal health passports have become a powerful tool that can be used to confirm the health status of travelers and meet the health entry requirements of different countries and regions. Personal health passports can contain Healthcare and machine learning information and vaccination records for effective management and monitoring of Healthcare and machine learning [5]. Traditional paper health passports can be traced back to the “health pass” issued during the European plague pandemic in the 15th century, which was intended to exempt travellers from quarantine measures. However, traditional paper health passports have the hidden danger of being easily forged and tampered with, leading to problems of insecurity and credibility. Especially in the digital age, the mobility and vulnerability of information further exacerbate these problems. In this context, some countries and international organizations have successively launched electronic health passports or health passports to allow work and travel abroad without compromising personal or Healthcare and machine learning. With the introduction of electronic health passports, the privacy leakage of personal information has become increasingly prominent. Traditional central storage architectures often Healthcare device data on third-party platforms. Once the third party is hacked or colluded with malicious attackers, the privacy and security of users will be difficult to guarantee [6]. Therefore, the protection of Healthcare device data and the management of privacy risks have become urgent issues to be addressed. At the same time, the Healthcare device data of various medical institutions and even countries are not interoperable, resulting in the formation of “information islands”, which greatly limits the sharing of health passports around the world. Blockchain technology has been introduced into the field of smart medical care [7–9] by many scholars due to its inherent advantages such as difficulty in tampering, transparency and decentralization, bringing new possibilities for the management and verification of health passports [10]. However, the contradiction between the low throughput and efficiency of traditional blockchains and the high efficiency required by the actual application scenarios of health passports has not been resolved. Secondly, although searchable encryption technology allows users to Healthcare device data and upload it to the cloud server and retrieve ciphertext [11], users often use resource-constrained mobile devices, which cannot meet the large cryptographic computing burden brought by existing solutions. While cloud-based systems are widely used for health data storage, they rely on centralized architectures, making them vulnerable to single points of failure, unauthorized access, and large-scale data breaches. Additionally, centralized models struggle with interoperability, limiting seamless data exchange across healthcare institutions. In contrast, blockchain offers tamper-proof records through cryptographic hashing, decentralized control to eliminate reliance on third parties, and transparent yet privacy-preserving verification via smart contracts. Unlike cloud systems, blockchain ensures data integrity, where modifications are impossible without consensus, significantly reducing forgery risks in health passports. To address these difficulties, this article suggests a system for storing, sharing, and verifying personal health passports that is based on the blockchain. The main contributions of this work are as follows: 1.

Hybrid On-Chain and Off-Chain Storage Optimization: The proposed approach integrates searchable encryption with a hybrid storage model, where only the index is stored on the blockchain while encrypted healthcare data is securely managed in the Interplanetary File System (IPFS). This reduces on-chain storage overhead, enhances query efficiency, and enables scalable and privacy-preserving healthcare data management, addressing the limitations of conventional blockchain-based healthcare systems.

The structure of this paper is as follows: Section 2 discusses review of existing research, highlighting strengths, identifying gaps. Section 3 represents essential concepts and theories needed to understand the proposed research. Section 4 describes the system architecture, components, and their interactions. Section 5 discloses the detailed design and implementation strategies of the proposed solution. In Section 6, evaluation of system security against vulnerabilities and potential threats is mentioned. Section 7 introduces the assessment of system performance using metrics and comparative results. Finally, Section 8 concludes with findings, research contributions, and future work suggestions.

As a decentralized database [12], blockchain technology has been widely used in Healthcare and machine learning, financial services, and supply chain management [13]. In response to the sharing and verification of personal health passports, scholars have proposed many blockchain-based solutions. Demirbaga et al. [14] implement the Healthcare and Internet of Things (IoT) enable Healthcare device data management application GreenPass based on blockchain technology. Although the applications of Healthcare and machine learning status survey function was mentioned, its system model and detailed solution details were not introduced in depth. Jafari et al. [15] proposed a government-managed blockchain to store COVID-19 vaccination certificates, emphasizing the use of biometric authentication to enhance user anonymity and privacy protection. Ait Bennacer et al. [1] proposed a digital health passport based on a private chain, which contains antibody test results and timestamps, but private chains are not suitable for international entry and exit scenarios. Zarour et al. [16] proposed a solution VacciFi takes into account the general Healthcare device data protection regulation (GDPR), and the architecture is scalable. At the same time, the solution is committed to using a permissioned blockchain to ensure the availability, traceability, and integrity of Healthcare and machine learning information, but the solution fails to deal well with internal attacks. Guerar et al. [17] proposed a global architecture that uses blockchain to verify and distribute different health passports. Rajtar et al. [18] proposed an online passport system to report citizens’ Healthcare and machine learning status. The scheme uses the user’s biometric information (such as iris scan) to uniquely identify each user, while the blockchain stores the user’s Healthcare and machine learning information such as historical medical records. A blockchain-based system for storing and exchanging immunization records was developed in this study [19]. Data traceability is ensured by storing the immunization records on the blockchain. Another benefit of mutual authentication is that it ensures the Healthcare device data’s integrity and non-repudiation [20]. Consensus algorithms are an important component of blockchain systems and affect the overall operating efficiency of blockchain systems [21]. Among the most popular consensus algorithms currently in use are the Byzantine fault tolerance (BFT) protocol [22], proof of collateral [23], proof of assets [24], and proof of work [25]. When it comes to consortium chains, most consensus algorithms employ practical byzantine fault tolerance (PBFT) [21] consensus. Nevertheless, the network and the amount of time it takes for a message to reach agreement in the entire system are external elements that are bound to impact PBFT, being a strong consistency consensus mechanism. Consequently, wait times for individual nodes in a P2P network to reach consensus are similarly lengthened. Obviously, the global health passport information chain must have extremely high requirements for the throughput of the blockchain, which is difficult to meet with the traditional PBFT consensus mechanism. Therefore, it is very important to choose a consensus mechanism that is suitable for the current solution. Zhou et al. [26] proposed a weak consistency BFT consensus method by weakening the requirement for strong consistency in the consensus process. This method is based on an asynchronous BFT algorithm and only guarantees the relative position of the messages received and agreed upon by each node, without requiring the message order of each node to be completely consistent, thereby achieving consistency of the entire system, which also greatly improves the throughput of the entire blockchain. This solution improves the weak consistency BFT consensus method and further improves the efficiency. In summary, although scholars have proposed solutions to the sharing and verification problems of health passports, the existing solutions store a large amount of Healthcare device data in the blockchain, which increases the burden on blockchain nodes and reduces the efficiency of the overall solution. Especially in multi-user scenarios, frequent verification operations will further increase the time cost of the solution [27]. At the same time, for scenarios such as health passports that require frequent updates and verification of information, the existing solutions fail to fully consider the low throughput of traditional blockchains and cannot handle many user requests in a short period of time, thus affecting the real-time and accuracy of Healthcare and machine learning information. Therefore, there is an urgent need to seek a more efficient and sustainable method to improve the efficiency of the solution while ensuring security, and it should be able to take into account multiple dimensions such as confidentiality, integrity and multi-user scenarios. In order to more intuitively show the difference between our scheme and traditional schemes, our scheme is compared with some representative schemes [18] from multiple dimensions.

This section first focuses on the system model and entity functions, and then gives the threat model established in this paper and the security goals of the model.

In order to solve the privacy leakage problem faced by the current health passport in the process of sharing and verification, as well as the problem that the blockchain throughput is low and cannot match the real-time performance of smart medical care, this section gives a specific solution design. The solution considers the multi-user scenario where users travel in groups, and divides the solution into two scenarios: single user and multi-user. The solution mainly includes four stages: system initialization, health passport encryption and storage, health passport update, and health passport verification. The symbols are shown in Table 1.

This section first compares the functions of this scheme with related health passport schemes; then analyzes the computational overhead of this scheme from a theoretical perspective and compares it with existing schemes; finally, evaluates the performance of the scheme through simulation experiments.

This paper addresses critical challenges in the global sharing of personal health passports, including “information islands,” inadequate privacy protection, and risks of forgery. To overcome these, a blockchain-based solution for health passport storage, sharing, and verification is proposed, integrating searchable encryption technology with blockchain to ensure secure, efficient, and scalable data management. The proposed scheme introduces an innovative combination of on-chain and off-chain storage using IPFS, enhancing storage optimization while maintaining reliability. Additionally, an improved aggregate signature mechanism is employed to facilitate efficient multi-user verification, while a two-stage weak consensus algorithm significantly improves blockchain throughput and reduces communication complexity. Through comprehensive security analysis and experimental validation, the scheme demonstrates notable advantages, achieving up to 49.89% optimization in computational overhead and up to 25.81% reduction in communication overhead in multi-user scenarios. However, challenges remain in single-user cases, where retrieval and signature verification overheads are higher than existing solutions. To address this, future research will explore lightweight cryptographic operations and hybrid storage mechanisms to enhance efficiency in low-volume transactions. Furthermore, ethical and legal considerations are paramount in blockchain-based healthcare systems. Our approach ensures compliance with GDPR and HIPAA by utilizing off-chain storage for sensitive data while maintaining secure on-chain references. To address blockchain immutability challenges, potential solutions include zero-knowledge proofs, revocable encryption, and hybrid blockchain governance models to uphold user privacy and the right to data modification. Future research will refine privacy-preserving techniques, regulatory adaptability, and energy-efficient consensus mechanisms to enhance scalability and real-world applicability. By addressing key concerns in security, privacy, efficiency, and ethical compliance, this work presents a robust and adaptable framework for secure health passport management, with significant potential for global healthcare data interoperability and secure international travel.