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This work proposes a scalable, blockchain-based platform for the secure sharing of COVID-19 or other disease vaccination certificates. As an indicative use case, we simulate a large-scale deployment by considering the countries of the European Union. The proposed platform is evaluated through extensive simulations in terms of 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-\`a-vis the related work, the proposed platform is novel, especially through the prism of a large-scale, full-fledged implementation and its assessment., Comment: 10 pages, 5 figures, 1 table

The heterogeneity of Internet of Things (IoT) systems has so far prevented the definition of adequate standards, hence making it difficult to compare meaningfully the security degree of diverse architectural choices. This task can be nonetheless achieved with formal methodologies. However, the dedicated IoT literature shows no evidence of a universal model allowing the security evaluation of any arbitrary system. Based on these considerations, we propose a new model that aims at being global and all-encompassing. Our model can be used to fairly analyse the security level of different IoT systems and compare them in a significant way. It is designed to be adaptive with realistic definitions of the adversary’s (1) actions of interacting with IoT systems; (2) capabilities of accessing the data generated by and exchanged in IoT systems with established rules; and (3) objectives of attacking IoT systems according to the four recognised security properties of confidentiality, integrity, availability and soundness. Such a design enables the straightforward characterization of new adversaries. It further helps in providing a fine-grained security evaluation of IoT systems by either accurately describing attacks against the analysed systems or formally proving their guaranteed level of security.

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 has been sprouted, followed by relevant app implementations adopted by governments worldwide. Bluetooth, and 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 it 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., 34 pages, 3 figures

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.

The rise of wireless applications based on RFID has brought up major concerns on privacy. Indeed nowadays, when such an application is deployed, informed customers yearn for guarantees that their privacy will not be threatened. One formal way to perform this task is to assess the privacy level of the RFID application with a model. However, if the chosen model does not reflect the assumptions and requirements of the analyzed application, it may misevaluate its privacy level. Therefore, selecting the most appropriate model among all the existing ones is not an easy task. This paper investigates the eight most well-known RFID privacy models and thoroughly examines their advantages and drawbacks in three steps. Firstly, five RFID authentication protocols are analyzed with these models. This discloses a main worry: although these protocols intuitively ensure different privacy levels, no model is able to accurately distinguish them. Secondly, these models are grouped according to their features (e.g., tag corruption ability). This classification reveals the most appropriate candidate model(s) to be used for a privacy analysis when one of these features is especially required. Furthermore, it points out that none of the models are comprehensive. Hence, some combinations of features may not match any model. Finally, the privacy properties of the eight models are compared in order to provide an overall view of their relations. This part highlights that no model globally outclasses the other ones. Considering the required properties of an application, the thorough study provided in this paper aims to assist system designers to choose the best suited model.

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. We introduce a privacy-friendly authentication protocol that is able to maintain the security level in case of compromised readers, but also gradually restores the privacy thanks to the mobility of the customers in the system. We provide a thorough security analysis and a precise performance evaluation of our proposal. The efficiency of our solution is also demonstrated on a real-life case: we analyze the logs of 55 offline readers used during a 3-day sport event in 2010 that involved more than 100,000 tags.

Authentication for low-cost Radio-Frequency IDentification (RFID) is a booming research topic. The challenge is to develop secure protocols using lightweight cryptography, yet ensuring privacy. A current trend is to design such protocols upon the Learning Parity from Noise (LPN) problem. The first who introduced this solution were Hopper and Blum in 2001. Since then, many protocols have been designed, especially the protocol of Halevi, Saxena, and Halevi (HSH) [15] that combines LPN and the tree-based key infrastructure suggested by Molnar and Wagner [24]. In this paper, we introduce a new RFID authentication protocol that is less resource consuming than HSH, relying on the same adversary model and security level, though. Afterwards, we show that, if an adversary can tamper with some tags, the privacy claimed in HSH is defeated. In other words, either tags are tamper-resistant, then we suggest a protocol more efficient than HSH, or they are not, then we suggest a significative attack against the untraceability property of HSH.

Privacy is one of the most important security concerns in radio frequency identification. The publication of hundred RFID-based authentication protocols during the last decade raised the need of designing a dedicated privacy model. An important step has been done with the model of Vaudenay that combines early models into a unified and powerful one. In particular, this model addresses the case where an adversary is able to know whether or not the protocol execution succeeded. This modelizes the fact that the adversary may get information from a side channel about the termination of the protocol, e.g., she notices that the access is granted to the RFID-tag holder. We go one step forward in this paper and stress that the adversary may also have access to a side channel that leaks the computational time of the reader. This modelizes an adversary who measures how long it takes to grant the access. Although this channel could be seen as an implementation flaw, we consider that it is always risky to require the implementation to solve what the design should deal with. This new channel enables to demonstrate that many key-reference protocols are not as privacy-friendly as they claim to be, e.g., WSRE, OSK, C2, O-FRAP, O-FRAKE,... We then introduce the TIMEFUL oracle in the model of Vaudenay, which allows to analyze the resistance of the protocols to time-based attacks as soon as the design phase. Finally, we suggest some methods that make RFID-based authentication protocols immune to such attacks.

RFID-based access control solutions for mobile environments, e.g. ticketing systems for sport events, commonly rely on readers that are not continuously connected to the back-end system. The readers must so be able to perform their tasks even in offline mode, what commonly requires the management by the readers of sensitive data. We stress in this paper the problem of compromised readers and its impact in practice. We provide a thorough review of the existing authentication protocols faced to this constraint, and extend our analysis with the privacy property. We show that none of the reviewed protocols fits the required properties in case of compromised readers. We then design a sporadically-online solution that meets our expectations in terms of both security and privacy.