A Network-Aware Distributed Membership Protocol for Collaborative Defense

To counteract current trends in network malware, distributed solutions have been developed that harness the power of collaborative end-host sensors. While these systems greatly increase the ability to defend against attack, this comes at the cost of complexity due to the coordination of distributed hosts across the dynamic network. Many previous solutions for distributed membership maintenance are agnostic to network conditions and have high overhead, making them less than ideal in the dynamic enterprise environment. In this work, we propose a network-aware, distributed membership protocol, CLUSTER, which improves the performance of the overlay system by biasing neighbor selection towards beneficial nodes based on multiple system metrics and network social patterns (of devices and their users). We provide an extensible method for aggregating and comparing multiple, possibly unrelated metrics. We demonstrate the effectiveness and utility of our protocol through simulation using real-world data and topologies. As part of our results, we highlight our analysis of node churn statistics, offering a new distribution to accurately model enterprise churn

Anti-Persistence on Persistent Storage: History-Independent Sparse Tables and Dictionaries

International audienceWe present history-independent alternatives to a B-tree, the primary indexing data structure used in databases. A data structure is history independent (HI) if it is impossible to deduce any information by examining the bit representation of the data structure that is not already available through the API. We show how to build a history-independent cache-oblivious B-tree and a history-independent external-memory skip list. One of the main contributions is a data structure we build on the way—a history-independent packed-memory array (PMA). The PMA supports efficient range queries, one of the most important operations for answering database queries. Our HI PMA matches the asymptotic bounds of prior non-HI packed-memory arrays and sparse tables. Specifically, a PMA maintains a dynamic set of elements in sorted order in a linear-sized array. Inserts and deletes take an amortized O(log^2 N) element moves with high probability. Simple experiments with our implementation of HI PMAs corroborate our theoretical analysis. Comparisons to regular PMAs give preliminary indications that the practical cost of adding history-independence is not too large. Our HI cache-oblivious B-tree bounds match those of prior non-* HI cache-oblivious B-trees. Searches take O(log_B N) I/Os; inserts and deletes take O((log^2 N)/B + log_B N) amortized I/Os with high probability; and range queries returning k elements take O(log_B N + k/B) I/Os. Our HI external-memory skip list achieves optimal bounds with high probability, analogous to in-memory skip lists: O(log_B N) I/Os for point queries and amortized O(log_B N) I/Os for in-serts/deletes. Range queries returning k elements run in O(log_B N + k/B) I/Os. In contrast, the best possible high-probability bounds for inserting into the folklore B-skip list, which promotes elements with probability 1/B, is just Θ(log N) I/Os. This is no better than the bounds one gets from running an in-memory skip list in external memory

The structure and function of Alzheimer's gamma secretase enzyme complex

The production and accumulation of the beta amyloid protein (Aβ) is a key event in the cascade of oxidative and inflammatory processes that characterizes Alzheimer’s disease (AD). A multi-subunit enzyme complex, referred to as gamma (γ) secretase, plays a pivotal role in the generation of Aβ from its parent molecule, the amyloid precursor protein (APP). Four core components (presenilin, nicastrin, aph-1, and pen-2) interact in a high-molecular-weight complex to perform intramembrane proteolysis on a number of membrane-bound proteins, including APP and Notch. Inhibitors and modulators of this enzyme have been assessed for their therapeutic benefit in AD. However, although these agents reduce Aβ levels, the majority have been shown to have severe side effects in pre-clinical animal studies, most likely due to the enzymes role in processing other proteins involved in normal cellular function. Current research is directed at understanding this enzyme and, in particular, at elucidating the roles that each of the core proteins plays in its function. In addition, a number of interacting proteins that are not components of γ-secretase also appear to play important roles in modulating enzyme activity. This review will discuss the structural and functional complexity of the γ-secretase enzyme and the effects of inhibiting its activity

On the Accuracy of Decentralized Virtual Coordinate Systems in Adversarial Networks

Virtual coordinate systems provide an accurate and efficient service that allows hosts on the Internet to determine the latency to arbitrary hosts without actively monitoring all nodes in the network. Many of the proposed virtual coordinate systems were designed with the assumption that all of the nodes in the system are altruistic. However, this assumption may be violated by compromised nodes acting maliciously to degrade the accuracy of the coordinate system. As numerous peer-to-peer applications rely on virtual coordinate systems to achieve good performance, it is critical to address the security of such systems. In this work, we demonstrate the vulnerability of decentralized virtual coordinate systems to insider (or Byzantine) attacks. We propose techniques to make the coordinate assignment robust to malicious attackers without increasing the communication cost. We demonstrate the attacks and mitigation techniques in the context of a well-known distributed virtual coordinate system using simulations based on three representative, real-life Internet topologies of hosts and corresponding round trip times (RTT)

Robust Virtual Coordinate Systems with Byzantine Participants

Abstract — Virtual coordinate systems provide an accurate and efficient service that allows hosts on the Internet to determine the latency between arbitrary hosts without using active monitoring of all nodes in the network. Many of the proposed virtual coordinate systems were designed with the assumption that all of the nodes in the system are cooperative. However, this assumption may be violated by compromised nodes acting maliciously to degrade the accuracy of the virtual coordinate systems. In this work, we demonstrate the vulnerability of decentralized virtual coordinate systems to insider (or Byzantine) attacks. We propose techniques to decrease the number of incorrect coordinate changes, thereby making coordinate assignment and maintenance robust to malicious attackers. We demonstrate the attacks and mitigation techniques in the context of a well-known distributed virtual coordinate system using simulations based on a representative, real-world data set of Internet latencies. I

A platform for creating efficient, robust, and resilient peer-to-peer systems

The rapid growth of communication environments such as the Internet has spurred the development of a wide range of systems and applications based on peer-to-peer ideologies. As these applications continue to evolve, there is an increasing effort towards improving their overall performance. This effort has led to the incorporation of measurement-based adaptivity mechanisms and network awareness into peer-to-peer applications, which can greatly increase peer-to-peer performance and dependability. Unfortunately, these mechanisms are often vulnerable to attack, making the entire solution less suitable for real-world deployment. In this dissertation, we study how to create robust systems components for adaptivity, network awareness, and responding to identified threats. These components can form the basis for creating efficient, high-performance, and resilient peer-to-peer systems