In the context of clients accessing a read/write shared object, persistency of a written value is a property stating that a value written into the object is always available unless overwritten by a successive write operation. This property can be easily guaranteed in a static distributed system provided that either a subset of processes implementing the object does not crash or processes can crash and then recover being able to retrieve their last state. Unfortunately the enforcing of this property in a potentially large scale and dynamic distributed system (e.g. a P2P system) is far from being trivial when considering the case in which processes implementing the object may fail or leave at any time without notifying any other process (i.e., the last state might not be retrievable). The paper introduces the notion of weak persistency that guarantees persistency of values when a system becomes quiescent (arrivals and departures subside). An implementation of a weakly-persistent object ensuring causal consistency is provided along with its correctness proof. The interest of causal consistency lies in the fact that, contrarily to atomic consistency, it can be maintained even during non-quiescent periods of the distributed system (i.e., when persistency is not guaranteed). 1.

Abstract—ParaMoise is a novel organisational model that permits to specify parallel and concurrent systems ’ organisation and reorganisation. Workflows, locks and multiple organisation managers are the entities that differentiate this model from it antecedent, the Moise+ framework. All these entities must be efficiently designed and implemented to ensure the practical usage of the theoretically formulated model. The main challenge here is the distributed synchronisation of workflows and locks, that will maximise the performance of the system. This paper presents and analyses different workflows and locks manage-ment approaches that can be used to achieve this goal: from basic centralised or middleware based solutions, towards truly decentralised coordination mechanisms. I.

For the past three decades, a wide variety of cryptographic protocols have been proposed to solve secure communication problems even in the presence of adver-saries. The range of this work varies from developing basic security primitives pro-viding confidentiality and authenticity to solving more complex, application-specific problems. However, when these protocols are deployed in practice, a significant challenge is to ensure not just security but also privacy throughout these protocols’ lifetime. As computer-based devices are more widely used and the Internet is more globally accessible, new types of applications and new types of privacy threats are being introduced. In addition, user privacy (or equivalently, key privacy) is more likely to be jeopardized in large-scale distributed applications because the absence of a central authority complicates control over these applications. In this dissertation, we consider three relevant cryptographic protocols facing user privacy threats when deployed in practice. First, we consider matchmaking protocols among strangers to enhance their privacy by introducing the “durability” and “perfect forward privacy ” properties. Second, we illustrate the fragility of for-