In recent times, with the advent of blockchain technology, there is an optimism surrounding the concept of self-sovereign identity which is regarded to have an influential effect on how we interact with each other over the Internet in future. There are a few works in the literature which examine different aspects of self-sovereign identity. Unfortunately, the existing works are not methodological and comprehensive at all. Moreover, there exist different notions of what the term self-sovereign identity means. To exploit its full potential, it is essential to ensure a common understanding in a formal way. This paper aims to achieve this goal by providing the first-ever formal and rigorous treatment of the concept of self-sovereign identity using a mathematical model. This paper examines the properties that a self-sovereign identity should have and explores the impact of self-sovereign identity over the laws of identity. It also highlights the essential life-cycles of an identity management system and inter-relates how the notion of self-sovereign identity can be applied in these life-cycles. In addition, the paper illustrates several envisioned flows involving a self-sovereign identity leveraging blockchain technology covering different aspects of an identity management system. All in all, this paper presents the first formal and comprehensive step toward an academic investigation of self-sovereign identity.INDEX TERMS Identity, identity management system, self-sovereign identity, blockchain.

Distributed Ledger Technology (DLT) has emerged as one of the most disruptive technologies in the last decade. It promises to change the way people do their business, track their products, and manage their personal data. Though the concept of DLT was first implemented in 2009 as Bitcoin, it has gained significant attention only in the past few years. During this time, different DLT enthusiasts and commercial companies have proposed and developed several DLT platforms. These platforms are usually categorized as public vs private, general purpose vs application specific and so on. As a growing number of people are interested to build DLT applications, it is important to understand their underlying architecture and capabilities in order to determine which DLT platform should be leveraged for a specific DLT application. In addition, the platforms need to be evaluated and critically analyzed to assess their applicability, resiliency and sustainability in the long run. In this paper, we have surveyed several leading DLT platforms and evaluated their capabilities based on a number of quantitative and qualitative criteria. The comparative analysis presented in this paper will help the DLT developers and architects to choose the best platform as per their requirement(s). INDEX TERMS Distributed ledger technology, blockchain, immutability, DLT platforms.

Contact tracing has become a vital tool for public health officials to effectively combat the spread of new diseases, such as the novel coronavirus disease COVID-19. Contact tracing is not new to epidemiologist rather, it used manual or semi-manual approaches that are incredibly time-consuming, costly and inefficient. It mostly relies on human memory while scalability is a significant challenge in tackling pandemics. The unprecedented health and socio-economic impacts led researchers and practitioners around the world to search for technology-based approaches for providing scalable and timely answers. Smartphones and associated digital technologies have the potential to provide a better approach due to their high level of penetration, coupled with mobility. While data-driven solutions are extremely powerful, the fear among citizens is that information like location or proximity associated with other personal data can be weaponised by the states to enforce surveillance. Low adoption rate of such apps due to the lack of trust questioned the efficacy and demanded researchers to find innovative solution for building digital-trust, and appropriately balancing privacy and accuracy of data. In this paper, we have critically reviewed such protocols and apps to identify the strength and weakness of each approach. Finally, we have penned down our recommendations to make the future contact tracing mechanisms more universally inter-operable and privacy-preserving.

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The Internet of Things (IoT) is experiencing an exponential growth in a wide variety of usecases in multiple application domains, such as healthcare, agriculture, smart cities, smart homes, supply chain and so on. To harness its full potential, it must be based upon a resilient network architecture with strong support for security, privacy and trust. Most of these issues still remain to be addressed carefully for the IoT systems. Blockchain technology has recently emerged as a breakthrough technology with the potential to deliver some valuable properties such as resiliency, support for integrity, anonymity, decentralisation and autonomous control. A number of blockchain platforms are proposed that may be suitable for di erent use-cases including IoT applications. In such, the possibility to integrate the IoT and blockchain technology is seen as a potential solution to address some crucial issues. However, to achieve this, there must be a clear understanding of the requirements of di erent IoT applications and the suitability of a blockchain platform for a particular application satisfying its underlying requirements. This chapter aims to achieve this goal by describing an evaluation framework which can be utilised to select a suitable blockchain platform for a given IoT application.

In this paper, we present a comparative analysis of a few popular Identity Management Systems against a set of requirements. Identity Management and Identity Management Systems have gained significant attention in recent years with the proliferation of different web-enabled and e-commerce services leading to an extensive research on the field in the form of several projects producing many standards, prototypes and application models both in the academia and the industry. We have collected and compiled different requirements from different sources to profile an extensive set of requirements that are required for a Privacy-Enhancing Identity Management System and presented them in the form of a taxonomy. Then we have compared some Identity Management Systems against those requirements and presented them in a concise way to help readers find out instantly which systems satisfy what requirements and thus help them to choose the correct one to fit into their own scenarios.

Abstract-Cloud federation is an emergent cloud-computing paradigm where partner organisations share data and services hosted on their own clouds platforms. In this context, it is crucial to enforce access control policies that satisfy the data protection and privacy requirements of the partner organisations. However, due to the distributed nature of cloud federations, the access control system alone does not guarantee that its deployed components cannot be circumvented while processing access requests. Therefore, in order to promote accountability and transparency of access control decisions in federated clouds, we present a decentralised runtime monitoring architecture based on a blockchain technology. The logging components and data of the proposed infrastructure are deployed on the blockchain. This guarantees that the runtime monitoring components and the access logs cannot be compromised by malicious users to disguise their actions. We evaluate the performance of the runtime monitoring infrastructure with respect to detecting policy violations, and the cost of deploying the logging components and data on the blockchain.

We describe a federated identity management service that allows users to access organisational resources using their existing login accounts at social networking and other sites, without compromising the security of the organisation's resources. We utilise and extend the Level of Assurance (LoA) concept to ensure the organisation's site remains secure. Users are empowered to link together their various accounts, including their organizational one with an external one, so that the strongest registration procedure of one linked account can be leveraged by the other sites' login processes that have less stringent registration procedures. Coupled with attribute release from their organizational account, this allows users to escalate their privileges due to either an increased LoA, or additional attributes, or both. The conceptual and architectural designs are described, followed by the implementation details, the user trials we carried out, and a discussion of the current limitations of the system.