# Privacy-Preserving Solution for European Union Digital Vaccine Certificates
## 2 Related Work
Nevertheless, only the following data can be inputted into the wallet: (1) SMART Health card, (2) Good Health Pass, and (3) IBM Digital Health Pass credentials ([[https://www.ibm.com/downloads/cas/EVD69](https://www.ibm.com/downloads/cas/EVD69) GQ0]([https://www.ibm.com/downloads/cas/EVD69](https://www.ibm.com/downloads/cas/EVD69) GQ0), accessed on 5 March 2023). Consequently, it is therefore not possible to load a standard European vaccination certificate onto the system. According to IBM, the application does not hold any information that would link the presented data to the person in question. The user application is freely available for Android devices through the Google Play application. This solution is integrated into Amadeus' Traveler ID system. The CoronaCheck app [9] is the official CovidPass app of the Netherlands. Its functionality is similar to CTeka and Teka. These are two separate applications for proof and verification of COVID certificates. However, the application takes into account the protection of personal data. The verifier application, CoronaCheck Scanner, does not show all the data read from the certificate. After identity verification, it only reveals the initial letters of the user's first and last name, along with the day and month of birth, while keeping the year concealed. The COOV app [10] is South Korea's solution to the COVID Pass app. The application is focused on the protection of personal data. The vaccination certificate against COVID-19 is just one of the attributes that can be used to authenticate with this application. In addition to vaccination status and test results, this application can also be used to prove maturity. PASS-INFRA, which includes the COOV application, is a freely available solution and can also be used outside the Republic of South Korea. This solution uses a blockchain technology called InfraBlockchain [11]. This technology is independent of native cryptocurrencies, so it is suitable for this use. The technology is developed by Blockchain Labs, which is an active member of the Decentralized Identity Fund (DIF) foundation. According to [PERSON] [8], IRMA [12] technology, with the modified Idemix [13] attribute-based authentication scheme, has been already used in Dutch COVID-19 credentials ensuring strong privacy. Nevertheless, as EU DCCs do not support IRMA/Idemix technology, there can be a problem when borders are crossed. COVID Credentials Initiative (CCI) [14], as an open global community, collaborates on issuing open-standard-based privacy-preserving credentials and other related technologies for public health purposes. CCI deploys Verifiable Credentials (VCs) for representing user health and personal information in a digital, trustful, and tamper-evident manner. In the recent years, numerous research works in the literature have adopted blockchain and smart contract technologies, with the aim of harnessing the high availability, immutability, and traceability features that stem from utilizing a distributed public ledger [2]. Early decentralized approaches using Decentralized Identifiers (DIDs), public ledgers, and VCs have been analyzed by [PERSON] [15]. The work points to several issues such as lacking advanced cryptography or putting personal data on the blockchains. The work also raises ethical questions related to the use of immunity passports. Recently, [PERSON] et al. [16] proposed a privacy-preserving vaccination pass solution based on a self-sovereign identity concept with decentralized identifiers, VCs, zero-knowledge proofs, and blockchain. Their implemented prototype uses the Sovrin blockchain; Hyperledger Indy; JavaScript-based websites; Aries agents; Near-Field Communication (NFC) and Quick Response (QR) codes for local transfer of data; and digital wallet (connect.me) that is capable of managing VCs.