एक प्रतिरक्षा पासपोर्ट योजना आधारित द दोहरी-ब्लॉकचेन आर्किटेक्चर अंतर्राष्ट्रीय यात्रा के लिए

The implementation of immunity passports has been hampered by controversies over vaccines in various countries, the privacy of vaccinators, and the forgery of passports. While some existing schemes have been devoted to accelerating this effort, the problems above are not well solved in existing schemes. In this paper, we present an immunity passport scheme based on the dual-blockchain architecture, which frees people from the cumbersome epidemic prevention process while traveling abroad. Especially, the dual-blockchain architecture is established to fit with the scenarios of an immunity passport. Searchable encryption and anonymous authentication are utilized to ensure users' privacy. In addition, the performance and security evaluations show that our scheme achieves the proposed security goals and surpasses other authentication schemes in communication and computational overheads.

In our literature, we found that cistanche can also improve immunity. It contains a variety of active ingredients, such as cistanche ketone, cistanche glycoside, cistanchein, etc. These ingredients can regulate the function of the immune system and enhance the resistance of the immune system, against the invasion of foreign pathogens such as viruses and bacteria. In addition, Cistanche also has anti-oxidation, anti-tumor, anti-inflammatory, anti-fatigue, and other effects, which can help the body better cope with various challenges and improve the body's immunity.

1. Introduction

The Coronavirus Disease 2019 (COVID-19) pandemic is undoubtedly an unprecedented disaster for human society [1–3]. The pandemic is rapidly spreading and getting worse in many countries and regions of the world, which has caused a large number of infections and deaths. Countries around the world are doing their utmost to curb the spread of the pandemic, enacting strict policies such as quarantine for infected people, prohibitions on mass gatherings, restrictions on entry-exit, and so on.

Vaccination, in combination with personal protection, is the most effective measure to prevent COVID-19 [4]. However, the effectiveness of some vaccines remains controversial in countries because of differences in policies, technical standards, and religions. As shown by recent publications, not everyone holds a positive attitude toward the COVID-19 vaccine [5, 6]. There is even discrimination against unvaccinated people in some areas, which is called the stigmatization of vaccination [7, 8].

Restoring the order of human society in the post-epidemic era is one of the most important issues, among which lifting restrictions on people's entry-exit is particularly significant. The restrictions on the people who have been vaccinated could be relaxed [9]. Therefore, several countries and organizations have launched the immunity passport that allows them to work and travel abroad without compromising personal or public health [8, 10]. However, some serious issues remain unresolved: (1) traditional passports are easy to falsify. (2) There are controversies about the effectiveness of some vaccines in different countries. (3) Under the premise of stigmatization, vaccinators' privacy is still at risk.

To effectively ensure the privacy of people traveling during the COVID-19 pandemic, we propose an immunity passport scheme in this paper. In our scheme, vaccinated people can show their passports to a staff of customs without compromising their privacy for entry and exit. Our contributions are summarized as follows:

(1) To adapt our scheme to international travel scenarios, we designed a dual-blockchain architecture with two different types of blockchains, domestic and international. Different countries participate in the consensus of the international blockchain, which is conducive to solving controversies about vaccines.

(2) We leveraged the use of the inherent characteristics of blockchain to make the immunity passport traceable and nonrefundable. And for the purpose that users can have control over their data, we combined searchable encryption and anonymous authentication with blockchain.

(3) Our scheme allows users to participate in vaccination, authentication, and other processes using legitimate pseudonyms, which can well solve the stigmatization of vaccination.

(4) To prove the feasibility and reliability of our scheme, we conducted a complete security analysis and simulation experiments, including computational overheads, communication overheads, and energy overheads.

The rest of this paper is organized as follows. Section 2 discusses some related research achievements. Section 3 describes the preliminary knowledge and introduces the design details of the system model. The immunity passport scheme is proposed in Section 4. Section 5 presents the correctness and security analysis. Section 6 presents the performance evaluation, and Section 7 concludes this paper.

2. Related Work

Due to its outstanding characteristics, blockchain technology has attracted widespread attention in many fields including medical care, identity authentication, and finance [11–13]. Recently, there have been some studies applying blockchain technology to meet the challenges of COVID-19. Xu et al. [14] proposed a blockchain-enabled privacy-preserving contact tracing scheme, in which users' privacy is ensured by the pseudonym. However, their scheme has a high demand for the intensive computation of blockchain nodes. To control the spread of COVID-19, a privacy anonymous IoT model using blockchain was presented in [15]. 

In this scheme, people who wear RFID tags will be notified if they are near a possible or confirmed "hotspot" area. But the authors did not give a security analysis of the scheme in this paper. Song et al. [16] using Bluetooth technology designed a tracing and notification system based on blockchain and smart contracts to ensure users' privacy. 

However, there is an unreasonable assumption that people always honestly upload their health status to the blockchain. Jacob and Lawarée [17] pointed out that apps such as to StopCovid (France), NHS Covid-19 (UK), and Coronalert (Belgium) have security, political, and other issues. Although these schemes and applications are focused on addressing the issues of privacy, the public is still reluctant to disclose their data for privacy reasons [18, 19]. Moreover, contact tracing is a passive defense against the COVID-19 pandemic.

Hasan et al. [20] proposed a digital health passport system combining blockchain, proxy re-encryption, and smart contracts. In this system, the data owner grants access to other entities so that the user has control over his data. Based on blockchain, a framework was proposed in [21] to ensure users' privacy, which uses a locality-sensitive hash function to generate a secure identifier. The identifier can only be derived if the user provides his biometric and personal information, whereas, although the authors give details of the pseudo-identity generation, the description of the vaccination certificate is very brief. Angelopoulos et al. [22] presented a framework that used a private blockchain to store the digital health passport. But the authors did not give details about how to ensure users' privacy, and the characteristics of private blockchain did not apply to the scenarios where people travel among multiple countries.

None of the above research [20–22] addressed how the passport holder can verify the legality of inspectors, which is extremely important for users. Some existing authentication schemes are designed for scenarios such as the smart grid, the Internet of Things, and the smart medical [23–26]. Mahmood et al. [23] proposed an anonymous key agreement protocol for the smart grid infrastructure by using the identity-based signature. This protocol empowers the smart meters for anonymous information exchange with utility, which is proved secure under the random oracle model. A mutual authentication scheme focusing on mobile edge computing is proposed by Jia et al. [24], which only needs one massage exchange round to achieve mutual authentication. However, their scheme cannot achieve some security properties. Almadhoun et al. [25] proposed a decentralized and scalable authentication mechanism that utilizes blockchain-enabled fog nodes with connectivity to Ethereum smart contracts, which gives details of the smart contracts involved. Although all the above schemes have advantages and highlights, these authentication schemes are not suitable for the scenarios of an immunity passport.

It is noteworthy that the above schemes have some shortcomings when applied to epidemic prevention scenarios, which makes the privacy of users cannot guaranteed well. Therefore, it is meaningful to design a secure, reliable, and efficient immunization passport scheme for the COVID-19 epidemic.

3. System Model and Security Goals

In this section, we give a brief introduction to the basic theoretical knowledge involved in this paper, such as blockchain, searchable encryption, and bilinear mapping. Subsequently, the system model and security goals are presented. The system model is depicted in Figure 1, and the main notations that appear in the scheme are listed in Table 1.

3.1. Preliminaries. Blockchain.

Blockchain is a special kind of data structure that arranges a large number of blocks into a chain in chronological order, where each block is composed of certain data [27]. Blockchain is categorized roughly into the public blockchain, consortium blockchain, and private blockchain according to the degree of decentralization. Our scheme adopts the consortium blockchain because of the specific advantages: (1) it can be jointly controlled by multiple organizations or countries, which is suitable for the scenarios of our scheme. (2) Only the members of the consortium participate in the consensus, so it has high efficiency. (3) Not everyone can access the data on the consortium blockchain.

Bilinear Pairings. Let G1 and G2 be two multiplicative cyclic groups with the prime order as p. Let g be the generator of G1, which means G1=hi. We accept e as bilinear pairing if e : G1 × G1⟶G2 satisfies the following properties [28]:

3.2. सिस्टम मॉडल।

मॉडल ऑफ द इम्युनिटी पासपोर्ट%0अस्कीम%2सी आईटी यह माना जाता है कि विभिन्न महामारी रोकथाम%0एजेंसी (ईपीए) इन प्रत्येक देश फॉर्म एलायंस और संयुक्त रूप से%0ए ए घरेलू कंसोर्टियम ब्लॉकचेन 2सी वह 0ए 22 डोमेस्टिक ब्लॉकचेन (डीबीसी).'22 हर देश 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 000 000 00 00 0000 000 000 0000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 22 22 हर देश 0 0 0 0 0 0 0 0 0 22 देश 0 0 0 0 0 0 0 0 0 0 0 20 20 22 22 देश ब्लॉकचेन 0 देश 0 0 0 0 0 0 0 0 0 0 22 देश 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2002 ब्लॉकचेन 22 देश 0 0 0 0 0 0 0 " चूँकि हम उपयोग कंसोर्टियम ब्लॉकचेन टू डिज़ाइन सिस्टम मॉडल%2सी पॉपुलर कंसेंसस मैकेनिज्म अनुकूलित टू कंसोर्टियम ब्लॉकचेन कैन%0एबी रन ऑन हमारी स्कीमें%2सी जैसे प्रैक्टिकल बीजान्टिन फॉल्ट टॉलरेंस (पीबीएफटी) और प्रतिनिधि प्रूफ ऑफ स्टेक (डीपीओएस) 5बी29%2सी 0ए30%5डी मॉडल are वर्णित in detail as follow:

Key Generate Center (KGC). KGC एक संगठन के साथ उच्च विश्वसनीयता इन इस सिस्टम, जो जिम्मेदार है 0a जनरेटिंग सिस्टम पैरामीटर और डिस्ट्रीब्यूटिंग आंशिक प्राइवेट कुंजी सभी उपयोगकर्ताओं के लिए.

उपयोगकर्ता उपयोगकर्ता उपयोगकर्ता टीकाकरण ePA द्वारा कानूनी% 0apseudo-पहचान द्वारा उपयोगकर्ता a ट्रैपडोर और a डिक्रिप्शन कुंजी कर्मचारियों के लिए जब प्रतिरक्षा पासपोर्ट % 3b % 0athe सिफरटेक्स्ट पासपोर्ट द्वारा खोजा जाता है IBC नोड % 0a और द्वारा लौटाए गए IPFS द्वारा।

इंटर-प्लेनेटरी फाइल सिस्टम (आईपीएफएस) आईपीएफएस ए विकेंद्रीकृत फ़ाइल स्टोरेज नेटवर्क उपयोग स्टोर सिफरटेक्स्ट ऑफ पासपोर्ट जेनरेट द्वारा ईपीए द्वारा ।

महामारी रोकथाम एजेंसी (ईपीए) ईपीए रखरखाव ए % 0एडीबीसी इन प्रत्येक देश % 2 सी टीकाकरण के लिए जिम्मेदार टीकाकरण के लिए % 2 सी उत्पादन % c2% a0 प्रतिरक्षा पासपोर्ट % 2c और अपलोडिंग सिफरटेक्स्ट ऑफ पासपोर्ट आईपीएफएस और ईपीए भाग इन सहमति % 0aof DBC जनरेट नए ब्लॉक।

DBC नोड्स की भूमिका EPA प्रत्येक%0 देश और लेन-देन पर DBC पर प्रसारण EPA प्रसारण द्वारा ईपीए द्वारा निभाई जाती है।

अंतर्राष्ट्रीय ब्लॉकचेन (IBC) केवल एक IBC मौजूद है % 0 aour मॉडल में । IBC नोड्स की भूमिका संस्थानों द्वारा निभाई जाती है % 0aon देशों की ओर से 2c जैसे स्वास्थ्य मंत्रालय मंत्रालय स्वास्थ्य।

सीमा शुल्क विभाग के कर्मचारियों को सीमा शुल्क पासपोर्ट और डिक्रिप्ट पासपोर्ट प्राप्त करने के बाद यह उपयोगकर्ता%2सी जहां ए सेशन कुंजी इंटरवेंशन ट्रांसफर ट्रैपडोर और डिक्रिप्टन कुंजी के लिए बातचीत की जाती है

लेनदेन ऑन DBCs की संरचना 0aTable 2, में दिखाया गया है जिसमें पहचान EPA IDEPA जो उत्पन्न होता है DBC-लेनदेन, छद्म पहचान टीकाकार ID′, keyword-index fix, wg, हैश 0%s3%s3%s3%s3%s3%s3%s3%s3%c s3�%c s3%c s3�%s3%c s3%c s3%c s3%c 2c s3%c s3%c 2c s3%c s3%c 2c s3%c 2c s3%s3%c 2c 2c epa 2c 2c 0%c 2c 2c epa 2c epa idePA जो 0aDBC-transaction, छद्म पहचान इनोकुलेटर ID′, 0akeyword-index fix, wg, s3%s3%s3%s3%c s3%c s3%c s3%s3%c s3%c s3%c s3%c s3%c s3%c s3%c s3%c s3%s3%s3%s3% s3% s3% sgg 2c 2c 0% ePA 2c 2c epa idePA जो उत्पन्न करता है 0aDBC-transaction, छद्म पहचान इनोकुलेटर ID′, 0akeyword-index fix,

लेनदेन पर लेनदेन iBC की संरचना 0aTable 3, जिसमें देश IDctry शामिल है देश आईडीसीट्री जो जनरेट करता है the IBC-transaction, हस्ताक्षर ऑफ द देश साइनेटर, और sarch-index ðIDDB, ID′, फिक्स, कीवर्ड 2c कीवर्ड 2c कीवर्ड 2c 2c कीवर्ड देश आईडीसीट्री जो जनरेट करता है देश 2सी हस्ताक्षरकर्ता%2सी और हैश ऑफ द सिफरटेक्स्ट ऑफ द पासपोर्ट।

3.3. Security Goals.

We assumed that all blockchain nodes and customs staffs are semi-honest, and attackers can eavesdrop on messages while users are communicating with other entities. Based on this assumption, we propose the following security goals.

4. The Proposed Scheme

To facilitate readers a better understanding of the application scenario, we have made a brief overview of the scheme before describing the details. For the convenience of presentation, it is assumed that the entire process takes user U1 as an example, referring to Figure 1.

4.1. System Setup and User-Registration.

In this phase, KGC generates system parameters and its public-private key pair. The user obtains a legal pseudo identity and generates his full public-private key pair through the partial-private key generated by KGC (as shown in Figure 2).

4.2. Passport Generation and Storage.

In this phase, the EPA vaccinates the user and generates an immunity passport after authenticating the user's pseudo-identity, then stores the ciphertext of the passport on IPFS. Subsequently, different types of transactions will be uploaded to IBC and DBC.

4.3. पहचान प्रमाणीकरण और कुंजी समझौता।

इस%0एफ़ेज़, उपयोगकर्ता और सीमा शुल्क कर्मचारी प्रदर्शन पहचान प्रमाणीकरण से पुष्टि दोनों उन में से वैध, और a सुरक्षित sesion key is परवर्ती डेटा ट्रांसमिशन, as चित्रित इन चित्रा 3 के लिए बातचीत की जाती है.

5.2. सुरक्षा विश्लेषण।

गोपनीयता और गोपनीयता. हमारी%0अस्कीम, उपयोगकर्ता अन्य संस्थाओं द्वारा a legal छद्म पहचान के साथ इंटरैक्ट करता है. हमलावर अनुमान नहीं लगा सकता उपयोगकर्ता's वास्तविक पहचान ID′ जब तक कि वह दरारें उपयोगकर्ता's गुप्त कुंजी 0xi या यादृच्छिक संख्या %� 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 उपयोगकर्ता 27% वास्तविक%0ए पहचान आईडी′ जब तक कि वह क्रैक्स उपयोगकर्ता's गुप्त कुंजी 0xi या यादृच्छिक संख्या � 0 0 0 0 25 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 00 000 0000 000% 00 0 0 0 0 0 0 0 00 0 0 00 000 000 0000 0000 0000 0000 0000 0000 00000 0000 0000 0000 000 00 0 0 0 00 In the%0अस्टेप of "Passport-Search," केवल उपयोगकर्ता जनरेट a ट्रैपडोर और भेजें इसे to द स्टाफ सर्चिंग, और फिर, IPFS%0 रिटर्न संबंधित CP to कर्मचारियों के कर्मचारियों के लिए. इस प्रकार, उपयोगकर्ता उनके डेटा पर ful नियंत्रण उनके डेटा पर नियंत्रण होता है.

पारस्परिक प्रमाणीकरण. इन द चरण ऑफ "प्रमाणन और वार्ता," उपयोगकर्ता संकेत उसकी पहचान जानकारी के साथ निजी कुंजी स्की=ðxi, di Þ to get sigi ðUi, Vi Þ%0q 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRi 7d} ðRy 7d} ðRi 7d} ðRी 7d} ðRी 7d} ðRi 7d} ðRi 7d} ðRी 7d} ðRी 7d} ðRi 7d} ðRi 2c Xi Þ. इस step की शुद्धता में been ऊपर दिया गया है. इसलिए, स्कीम लक्ष्य of mutual ऑथेंटिकेशन प्राप्त करता है.

ट्रेसेबिलिटी और नॉनरिप्यूडेशन. इन हमारी स्कीम%2सी प्रत्येक उपयोगकर्ता'एस टीकाकरण अपलोड टू डीबीसी%0ए और आईबीसी. प्रत्येक लेन-देन निर्माता%2सी ज्ञात आईडीईपीए या आईडीसीट्री की पहचान आईडीईपीए या आईडीसी. एक बार उपयोगकर्ता ए स्वास्थ्य%0ए समस्या वैक्सीन वैक्सीन वैक्सीन वैक्सीन वैक्सीन 2सी वैक्सीन 2सी वैक्सीन 2सी वैक्सीन 2सी 20 20 20020 200 20 20 उपयोगकर्ता उपयोगकर्ता% उपयोगकर्ता उपयोगकर्ता 20 उपयोगकर्ता 20 उपयोगकर्ता उपयोगकर्ता उपयोगकर्ता% 20 20 20 20 20 उपयोगकर्ता

Insider Attack. KGC cannot reveal the private key ski of users because it is only responsible for generating partial private keys in the phase of "User-Registration." In addition, all the vaccination records will be uploaded to the blockchain, and the traceability and nonrepudiation characteristics ensure that blockchain nodes will not upload fake information.

6. Performance Evaluation

In this section, we make a functional property comparison between the proposed scheme and the existing immunity passport schemes [20–22]. Then, the proposed scheme is compared with the existing authentication schemes [23, 24] in terms of computational overheads, communicational overheads, and energy overheads.

6.1. Functional Comparison.

Table 4 shows the comparison of the functional properties of our scheme with other immunity passport schemes. From Table 4, we can see that all four schemes achieve access control of user data. Hasan et al.'s scheme [20] cannot provide anonymity, although blockchain is used in their scheme. Schemes in [21, 22] did not consider the issue of coordination between different departments in multiple countries in the scenarios of immunity passport. Moreover, schemes in [20–22] cannot provide mutual authentication between the user and the passport inspector. Our scheme achieves these functions well.

6.2. Overheads Comparison.

The computational complexity comparison of our scheme and schemes [23, 24] in the phase of authentication is shown in Table 5. Among them, Th, Tm, Te, Ta, and Tp, respectively, represent the time of hash function, point multiplication, modular exponentiation, point addition, and bilinear mappings.

For comparing the computational overheads, we conducted simulations on a PC with an Intel Core i{{0}}HQ CPU at 2.50 GHz and 8 GB RAM, running Windows 1{{10}} Home (64-bit). Simulations show that the operation time of Th, Tm, Te, Ta, and Tp, is about 0.0018 ms, 0.0012 ms, 0.0021 ms, 0.0127 ms, and 2.7737 ms, respectively. The computational overhead comparison of the user, other devices, and the total are shown in Figures 4, 5, and 6. 

As for the computation of users, a user in our scheme requires to calculate fUi ′, hi ′, Vi ′, kj, hj, eðVj, gÞ, Kg, that is 4 Th plus 3Tm plus 3Te plus Tp (2.7908 ms). Similarly, Mahmood et al.'s scheme [23] requires 3Th plus 2Tm plus 1Te plus Tp (2.7838 ms), and Jia et al.'s scheme [24] requires 5Th plus 4Tm plus 1Te plus Tp (2.7908 ms). Figure 4 shows that our scheme is similar to other schemes in terms of users' computational overheads. Comparing the computational overheads of other devices, our scheme requires calculating fki, hi ′,e ðVi ′, gÞ, Uj, hj, Vj, K, Confirg, that is 4Th plus 3Tm plus 3Te plus Tp (2.7908 ms). Similarly, scheme [23] requires 4Th plus 2Tm plus 1 Te plus 2Tp (5.5591 ms), and scheme [24] requires 5Th plus 5Tm plus 3Ta plus Tp (22.8268 ms). As can be seen from Figure 5, our scheme and scheme [24] are significantly better than scheme [23], because the number of bilinear mappings operation is reduced, which is time-consuming. Furthermore, it can be seen that the computational overheads of our scheme are equal between the users and other devices. As for the total computational overheads, our scheme performs similarly to the scheme [24], with a 33.10 percent reduction compared to the scheme [23], which can be seen in Figure 6.

that is 1280 bits. Similarly, scheme [23] needs to transmit 1312 bits during authentication; scheme [24] needs to transmit 1472 bits. We can see from Figure 7 that the performance of the communicational overhead of our scheme is a little different from the scheme [23]. However, our scheme only requires two rounds of massage exchange, whereas scheme [23] requires three rounds. And our scheme reduced 13.04 percent compared to the scheme [24] because the transmission of unnecessary information is reduced in our scheme, such as timestamps.

Energy overheads are also an important evaluation indicator. We use the voltage and current of the PC used in the simulations for comparing energy overheads, which are 1:2 V and 54:2 A, respectively. A hash function consumes 1:2 V ∗ 54:2 A ∗ 0:0018 ms {{10}}:1171 mj, a point multiplication consumes 1:2 V ∗ 54:2 A ∗ 0:0012 ms=0:0780 mj, modular exponentiation consumes 1:2 V ∗ 54:2 A ∗ 0:0021 ms = 0:1366 mj, a point addition consumes 1:2 V ∗ 54:2 A ∗ 0:0127 ms=0:8260 mj, and a bilinear mapping consumes 1:2 V ∗ 54:2 A ∗ 2:7737 ms=180:4014 mj. The total energy overheads comparison can be seen in Figure 8, which shows that the energy overheads of our scheme are almost equal to that of the scheme [24] and still better than that of the scheme [23].

7. Conclusion

In this paper, we propose an immunity passport scheme to mitigate the impact of COVID-19. This scheme helps people travel between different countries without going through tedious epidemic prevention procedures in this era of post epidemic. The highlight of this scheme is that it combines searchable encryption and authentication with blockchain, which ensures users' privacy and allows them to have control over their data. According to the security analysis, our scheme can well meet the security requirements of the immunity passport scenarios. Furthermore, the evaluation results show that compared with other schemes, our scheme has better communication and computing performance while achieving functional properties. Next, designing an efficient consensus mechanism and detailed smart contracts for this scheme is our future research direction.

Hancheng Gao and Haoyu Ji are the co-first authors.

This work is supported by the National Natural Science Foundation of China (grant numbers 62072252 and 61872194).

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