A Permissioned Distributed Ledger for Monitoring Web Content 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 longterm, 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 faulttolerance 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 arbitrarysized, 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 faulttolerant, tamperproof manner.

ResilientDB: Global Scale Resilient Blockchain Fabric Recent developments in blockchain technology have inspired innovative new designs in distributed resilient database systems. At their core, these database systems typically use Byzantine faulttolerant consensus protocols to maintain a common state across all replicas, even if some replicas are faulty or malicious. Unfortunately, existing consensus protocols are not designed to deal with geoscale deployments in which many replicas spread across a geographically large area participate in consensus. To address this, we present the GeoScale Byzantine FaultTolerant consensus protocol (GeoBFT). GeoBFT is designed for excellent scalability by using a topologicalaware grouping of replicas in local clusters, by introducing parallelization of consensus at the local level, and by minimizing communication between clusters. To validate our vision of highperformance geoscale resilient database systems using GeoBFT, we implement GeoBFT in our efficient ResilientDB blockchain and database fabric. We show that GeoBFT is not only sound and provides great scalability, but also outperforms stateoftheart consensus protocols by a factor of six in geoscale deployments.