1,720,959 research outputs found
Throttling Tor Bandwidth Parasites
No full textTor's network congestion and performance problems stem from a small percentage of users that consume a large fraction of available relay bandwidth. These users continuously drain relays of excess bandwidth, creating new network bottlenecks and exacerbating the effects of existing ones. Attacking the problem at its source, we present the design of three new algorithms that throttle clients to reduce network congestion and increase interactive client performance. Unlike existing techniques, our algorithms adaptively adjust throttling parameters given only information local to a relay. We implement our algorithms in Tor and compare significant client performance benefits using network-wide deployments of our algorithms under a variety of network loads. We also analyze the effects of throttling on anonymity and compare the security of our algorithms under adversarial attack. Software patches for our algorithms will be submitted to Tor.Jansen, Rob; Syverson, Paul; Hopper, Nicholas J.. (2011). Throttling Tor Bandwidth Parasites. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/215866
Shadow: Running Tor in a Box for Accurate and Efficient Experimentation
No full textTor is a large and popular overlay network providing both anonymity to its users and a platform for anonymous communication research. New design proposals and attacks on the system are challenging to test in the live network because of deployment issues and the risk of invading users' privacy, while alternative Tor experimentation techniques are limited in scale, are inaccurate, or create results that are difficult to reproduce or verify. We present the design and implementation of Shadow, an architecture for efficiently running accurate Tor experiments on a single machine. We validate Shadow's accuracy with a private Tor deployment on PlanetLab and a comparison to live network performance statistics. To demonstrate Shadow's powerful capabilities, we investigate circuit scheduling and find that the EWMA circuit scheduler reduces aggregate client performance under certain loads when deployed to the entire Tor network. Our software is open source and available for download.Jansen, Rob; Hopper, Nicholas J.. (2011). Shadow: Running Tor in a Box for Accurate and Efficient Experimentation. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/215867
The Distributed Virtual Network for High Fidelity, Large Scale Peer to Peer Network Simulation
No full textThe ability to analyze the behavior of large distributed systems can be limited by the modeling tools used. The Distributed Virtual Network (DVN) is a discrete event network simulator providing a platform for realistic, high fidelity, scalable and repeatable simulations of large distributed systems. With a global view of the network, it provides the ability to quantify the behavior of the system under stress and attack conditions. We present the architecture of the simulator along with the simulation results from a real world P2P protocol implementation ported to DVN. We also compare DVN with another similar tool, outlining the benefits of our contribution.Foo Kune, Denis; Malchow, Tyson; Tyra, James; Hopper, Nicholas J.; Kim, Yongdae. (2010). The Distributed Virtual Network for High Fidelity, Large Scale Peer to Peer Network Simulation. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/215847
Taking Routers Off Their Meds: Unstable Routers and the Buggy BGP Implementations That Cause Them
No full textBoth academic research and historical incidents have shown the impact of unstable BGP speakers on network performance and reliability. A large amount of time and energy has been invested improving router stability. In this paper, we show how an adversary in control of a BGP speaker in a transit AS can cause a victim router in an arbitrary location on the Internet to become unstable. Through experimentation with both hardware and software routers, we examine the behavior of routers under abnormal conditions and come to four conclusions. First, routers placed in certain states behave in anything but a stable manner. Second, unexpected but perfectly legal BGP messages can place routers into those states with disconcerting ease. Third, an adversary can use these messages to disrupt a victim router to which he is not directly connected. Fourth, modern best practices do little to prevent these attacks. These conclusions lead us to recommend more rigorous testing of BGP implementations, focusing as much on protocol correctness as software correctness.Schuchard, Max; Thompson, Christopher; Hopper, Nicholas J.; Kim, Yongdae. (2011). Taking Routers Off Their Meds: Unstable Routers and the Buggy BGP Implementations That Cause Them. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/215877
Censorship resistant overlay publishing
No full textThe fundamental requirement of censorship resistance is content availability and discoverability --- it should be easy for users to find and access documents. At the same time, participating storage providers should be unaware of what they are storing to preserve plausible deniability. Fulfilling these requirements simultaneously seems impossible --- how does a system maintain a searchable index of content for users and yet hide it from storage providers? These paradoxical requirements have been previously reconciled by requiring out-of-band communication to either find ways to connect to the system, locate files, or learn file decryption keys --- an unacceptable situation when easy content discovery is critical. This paper describes a design for a peer-to-peer, permanent, and unblockable content store which is easily searchable and yet self-contained, i.e. does not require out-of-band communication. To achieve this, we separate file data, metadata, and encryption keys such that someone searching for information about a specific topic can retrieve all three components and reconstruct the file, but someone who only stores at most two components can neither determine the nature of the file content nor locate the missing component. We begin by identifying the core requirements for unblockable storage systems to resist state-level Internet censorship, construct a system that fulfills those requirements, and analyze how it avoids the problem of prior attempts at censorship resistance. Finally, we present measurements of a deployed proof-of-concept implementation, demonstrating the feasibility of our design.Vasserman, Eugene Y.; Heorhiadi, Victor; Kim, Yongdae; Hopper, Nicholas J.. (2011). Censorship resistant overlay publishing. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/215874
Keep your friends close: Incorporating trust into social network-based Sybil defenses
No full textSocial network-based Sybil defenses exploit the algorithmic properties of social graphs to infer the extent to which an arbitrary node in such a graph should be trusted. However, these systems do not consider the different amounts of trust represented by different graphs, and different levels of trust between nodes, though trust is a crucial requirement in these systems. For instance, co-authors in an academic collaboration graph are trusted in a different manner than social friends. Furthermore, some social friends are more trusted than others. However, previous designs for social network-based Sybil defenses have not considered the inherent trust properties of the graphs they use. In this paper we introduce several designs to tune the performance of Sybil defenses by accounting for differential trust in social graphs and modeling these trust values by biasing random walks performed on these graphs. Surprisingly, we find that the cost function, the required length of random walks to accept all honest nodes with overwhelming probability, is much greater in graphs with high trust values, such as co-author graphs, than in graphs with low trust values such as online social networks. We show that this behavior is due to the greater number of close-knit communities in high-trust graphs, requiring longer walk to traverse multiple communities. Furthermore, we show that our proposed designs to account for trust increase the cost function of graphs with low trust value.Mohaisen, Abedelaziz; Hopper, Nicholas J.; Kim, Yongdae. (2010). Keep your friends close: Incorporating trust into social network-based Sybil defenses. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/215837
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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