Abstract: We describe the design, implementation, and evaluation of Depot, a cloud storage system that minimizes trust assumptions. Depot assumes less than any prior system about the correct operation of participating hosts—Depot tolerates Byzantine failures, including malicious or buggy behavior, by any number of clients or servers—yet provides safety and availability guarantees (on consistency, staleness, durability, and recovery) that are useful. The key to safeguarding safety without sacrificing availability (and vice versa) in this environment is to join forks: participants (clients and servers) that observe inconsistent behaviors by other participants can join their forked view into a single view that is consistent with what each individually observed. Our experimental evaluation suggests that the costs of protecting the system are modest. Depot adds a few hundred bytes of metadata to each update and each stored object, and requires hashing and signing each update. 1

To achieve the vision of networks that work without any supporting infrastructure, we need wireless ad hoc technology to replace the cabling infrastructure, but we also need self-configuring network and application services to replace the server infrastructure. Current solutions perform poorly because they either pick a single host to act as the server or they use network wide broadcasts to implement services. We need wireless ad hoc networks with zero servers and zero broadcasts! Can we use DHTs to build both network- and applicationlevel services with zero servers and zero broadcasts? This paper starts to answer this question. It shows that it is important to remove broadcasts at all levels of the networking stack and describes how to use the Virtual Ring Routing protocol to achieve our vision.

Abstract. Object-oriented technologies are frequently used to design and implement distributed applications. Object replication is a well-established approach to increase the dependability for such applications. Generic replication infrastructures often fail to meet non-standard application-specific requirements such as support for client-side computing. Our FTflex replication infrastructure combines the fragmented object model with semantic annotations in order to customize and optimize replication mechanisms, and thus provides a more flexible replication infrastructure. This paper presents DiGit, a replicated version control system based on the architecture of Git. DiGit is implemented with the help of the FTflex infrastructure for object replication. The contributions of this paper are twofold. First, the paper evaluates the fitness of our replication framework for a specific, complex application. We identify two advantages of the replication infrastructure: the ability to provide client-side code as a conceptually integral part of a remote service, and support for an optimized protocol for remote interaction. As a second contribution, the paper presents a powerful replicated version control system and shows the lessons learned from using object replication in such a system. 1

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