During 2021, different worldwide initiatives have been established for the development of digital vaccination certificates to alleviate the restrictions associated with the COVID‐19 pandemic to vaccinated individuals. Although diverse technologies can be considered for the deployment of such certificates, the use of blockchain has been suggested as a promising approach due to its decentralization and transparency features. However, the proposed solutions often lack realistic experimental evaluation that could help to determine possible practical challenges for the deployment of a blockchain platform for this purpose. To fill this gap, this work introduces a scalable, blockchain‐based platform for the secure sharing of COVID‐19 or other disease vaccination certificates. As an indicative use case, we emulate a large‐scale deployment by considering the countries of the European Union. The platform is evaluated through extensive experiments measuring computing resource usage, network response time, and bandwidth. Based on the results, the proposed scheme shows satisfactory performance across all major evaluation criteria, suggesting that it can set the pace for real implementations. Vis‐à‐vis the related work, the proposed platform is novel, especially through the prism of a large‐scale, full‐fledged implementation and its assessment.

The coronavirus pandemic is a new reality, and it severely affects the modus vivendi of the international community. In this context, governments are rushing to devise or embrace novel surveillance mechanisms and monitoring systems to fight the outbreak. The development of digital tracing apps, which among others are aimed at automatising and globalising the prompt alerting of individuals at risk in a privacy-preserving manner, is a prominent example of this ongoing effort. Very promptly, a number of digital contact tracing architectures have been sprouted, followed by relevant app implementations adopted by governments worldwide. Bluetooth, specifically its Low Energy (BLE) power-conserving variant, has emerged as the most promising short-range wireless network technology to implement the contact tracing service. This work offers the first to our knowledge full-fledged review of the most concrete contact tracing architectures proposed so far in a global scale. This endeavour does not only embrace the diverse types of architectures and systems, namely, centralised, decentralised, or hybrid, but also equally addresses the client side, i.e., the apps that have been already deployed in Europe by each country. There is also a full-spectrum adversary model section, which does not only amalgamate the previous work in the topic but also brings new insights and angles to contemplate upon.

After several years of research on cryptographic models for privacy in RFID systems, it appears that no universally model exists yet. Experience shows that security experts usually prefer using their own ad-hoc model than the existing ones. In particular, the impossibility of the models to refine the privacy assessment of different protocols has been highlighted in several studies. The paper emphasizes the necessity to define a new model capable of comparing protocols meaningfully. It introduces an untraceability model that is operational where the previous models are not. The model aims to be easily usable to design proofs or describe attacks. This spirit led to a modular model where adversary actions (oracles), capabilities (selectors and restrictions), and goals (experiment) follow an intuitive and practical approach. This design enhances the ability to formalize new adversarial assumptions and future evolutions of the technology, and provide a finest privacy evaluation of protocols.

Authentication protocols are usually designed to face an adversary who is able to tamper with the channel, possibly with the prover, but rarely with the verifier. When considering large-scale RFID applications, e.g., mass transportation or ticketing, the last threat is no longer a fiction. A typical case is the loss or theft of a handheld reader. If the protocol is expected to be privacy-friendly, and run by offline readers, there is no solution currently to restore the privacy once the readers are compromised except renewing all the tags, which is definitely impractical.