In this paper, we present O3, a social link based private storage cloud for decentralized collaboration. O3allows users to share and collaborate on collections of files (shared folders) with others, in a decentralized manner, without the need for intermediaries (such as public cloud storage servers) to intervene. Thus, users can keep their working relationships (who they work with) and what they work on private from third parties. Using benchmarks and traces from real workloads, we experimentally evaluate O3and demonstrate that the system scales linearly when synchronizing increasing numbers of concurrent users, while performing on-par with the ext4 non-version-tracking filesystem.

In this paper, we present O3REAL, a privacy-preserving distributed middleware for real-time collaborative editing of documents. O3REAL introduces a novel approach for building peer-to-peer real-time collaborative applications, using a reliable broadcast channel mechanism for network communication, but at the same time provides for persistent storage management of collaborative documents using the filesystem interface of a POSIX compliant filesystem. This approach enables real-time, completely decentralized collaboration among users, without the need for a third party to intervene, and significantly simplifies the creation of peer-to-peer collaborative applications. We demonstrate that O3REAL scales well for real-time collaboration use-cases. For example, with 33 users simultaneously collaborating on a document in real time over a WAN with a 50 ms link delay, the average perceived latency is approximately 54 ms, which is very close to the optimal baseline. In comparison, Etherpad exhibits nearly twice the perceived latency.

Online publishing of news and information enables important content to reach a much larger audience than traditional paper publishing, but there is no guarantee of long-term, reliable, and persistent access to the content. Over time, links "decay" because they are not reliably updated when content changes location, or even worse, content is deliberately altered from its original published form or deleted altogether. We present the design of Watchdog, a permissioned distributed ledger that securely and reliably monitors and preserves dynamic web content such as government and news sites. Unlike prior preservation systems, our system design allows nodes to be dispersed across multiple administrative domains, thus eliminating single points of trust and at the same time, is the first to monitor how content changes both over time and across geographical location. Watchdog achieves Byzantine fault-tolerance via a novel interactive consistency algorithm that offers a twist on the traditional definition and use of interactive consistency; the algorithm enables a set of mutually suspicious nodes, with arbitrary-sized, potentially overlapping data collections, to efficiently agree on the exact data collection in possession by each node. We demonstrate how our algorithm enables Watchdog nodes to exchange and agree upon the content each has observed individually, in a fault-tolerant, tamper-proof manner.

We present the “It's My Data file system” (IMDfs), a personal, version-tracking, distributed file system that allows users to take custody of their cross-device data management needs, without depending on cloud storage providers. Such a system may be desirable to privacy-conscious users, who worry about the increasing number of cloud storage incidents involving data leakage and corruption, or simply want to synchronize their devices without depending on third parties. IMDfs provides a global, unified view of a user's distributed data collection from any device, user-controlled replication of data across devices, transparent remote access, and support for non-restrictive conflict management. IMDfs achieves all this without sacrificing fault-tolerance or performance and with modest storage overhead. We present the design, implementation, and detailed performance evaluation of IMDfs using benchmarks and traces from real workloads, and we demonstrate that: 1) IMDfs, as a local file system, has reasonable overhead compared with a FUSE loopback file system and Wayback, a local versioning file system, and 2) IMDfs, as a network file system, outperforms NFS and Ori, a state-of-the-art file system for cross-device data management.