Trust Management (TM) systems for authentication are vital to the security of online interactions, which are ubiquitous in our everyday lives. Various systems, like the Web PKI (X.509) and PGP’s Web of Trust are used to manage trust in this setting. In recent years, blockchain technology has been introduced as a panacea to our security problems, including that of authentication, without sufficient reasoning, as to its merits.In this work, we investigate the merits of using open distributed ledgers (ODLs), such as the one implemented by blockchain technology, for securing TM systems for authentication. We formally model such systems, and explore how blockchain can help mitigate attacks against them. After formal argumentation, we conclude that in the context of Trust Management for authentication, blockchain technology, and ODLs in general, can offer considerable advantages compared to previous approaches. Our analysis is, to the best of our knowledge, the first to formally model and argue about the security of TM systems for authentication, based on blockchain technology. To achieve this result, we first provide an abstract model for TM systems for authentication. Then, we show how this model can be conceptually encoded in a blockchain, by expressing it as a series of state transitions. As a next step, we examine five prevalent attacks on TM systems, and provide evidence that blockchain-based solutions can be beneficial to the security of such systems, by mitigating, or completely negating such attacks.

This thesis improves the state-of-the-art in anonymous Pub/Sub in several areas. In particular, the thesis addresses the following aspects of constructing anonymous Pub/Sub systems: (i.) Building blocks that reduce the complexity of constructing anonymous Pub/Sub systems are proposed; (ii.) methods for anonymously establishing Pub/Sub overlay networks are presented; (iii.) a method for inter-overlay optimization to distribute load is introduced; (iv.) methods for optimizing overlays regarding anonymity are proposed, and (v.) anonymity attacks and countermeasures are presented. […]

Publish-subscribe is an increasingly popular messaging pattern for distributed systems, supporting scalable and extensible programming, and optimal spatial, temporal, and control-flow decoupling of distributed components. Publish-subscribe middleware and methods were extended towards supporting security, in particular confidentiality, and increased availability, yet a few prior works addressed anonymity of participants. Anonymity of senders and receivers may however be crucial, e.g., for supporting freedom of expression in regimes where political repression and censorship prevail. In this article, we review basic security and privacy requirements and introduce a new attacker model based on statistical disclosure, used to challenge anonymity. We elaborate on design options for privacy-preserving publish-subscribe systems and present a novel system that leverages peer-to-peer networking concepts; this novel approach protects subscriber anonymity by means of Probabilistic Forwarding (PF) and through a novel so-called Shell Game (SG) algorithm. We verify our solution against the requirements and provide a simulation-based analysis of the effectiveness of our approaches in light of our attacker model. The results show that the SG algorithm efficiently protects subscriber anonymity, and that anonymity sets can be adjusted via PF.