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Articles 631 - 660 of 1103

Full-Text Articles in Computer Sciences

Structural Analysis Of Social Networks With Wireless Users, Guanling Chen, David Kotz Jul 2005

Structural Analysis Of Social Networks With Wireless Users, Guanling Chen, David Kotz

Computer Science Technical Reports

Online interactions between computer users form Internet-based social networks. In this paper we present a structural analysis of two such networks with wireless users. In one network the wireless users participate in a global file-sharing system, and in the other they interact with each other through a local music-streaming application.

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Managing Access Control In Virtual Private Networks, Twum Djin Jun 2005

Managing Access Control In Virtual Private Networks, Twum Djin

Dartmouth College Undergraduate Theses

Virtual Private Network technology allows remote network users to benefit from resources on a private network as if their host machines actually resided on the network. However, each resource on a network may also have its own access control policies, which may be completely unrelated to network access. Thus users� access to a network (even by VPN technology) does not guarantee their access to the sought resources. With the introduction of more complicated access privileges, such as delegated access, it is conceivable for a scenario to arise where a user can access a network remotely (because of direct permissions from …

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Lower Bounds On The Communication Complexity Of Shifting, Marco D. Adelfio Jun 2005

Lower Bounds On The Communication Complexity Of Shifting, Marco D. Adelfio

Dartmouth College Undergraduate Theses

We study the communication complexity of the SHIFT (equivalently, SUM-INDEX) function in a 3-party simultaneous message model. Alice and Bob share an n-bit string x and Alice holds an index i and Bob an index j. They must send messages to a referee who knows only n, i and j, enabling him to determine x[(i+j) mod n]. Surprisingly, it is possible to achieve nontrivial savings even with such a strong restriction: Bob can now make do with only ceil(n/2) bits. Here we show that this bound is completely tight, for all n. This is an exact lower bound, with no …

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On-Line Metasearch, Pooling, And System Evaluation, Robert A. Savell Jun 2005

On-Line Metasearch, Pooling, And System Evaluation, Robert A. Savell

Dartmouth College Ph.D Dissertations

This thesis presents a unified method for simultaneous solution of three problems in Information Retrieval--- metasearch (the fusion of ranked lists returned by retrieval systems to elicit improved performance), efficient system evaluation (the accurate evaluation of retrieval systems with small numbers of relevance judgements), and pooling or ``active sample selection" (the selection of documents for manual judgement in order to develop sample pools of high precision or pools suitable for assessing system quality). The thesis establishes a unified theoretical framework for addressing these three problems and naturally generalizes their solution to the on-line context by incorporating feedback in the form …

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Modeling Users' Mobility Among Wifi Access Points, Minkyong Kim, David Kotz Jun 2005

Modeling Users' Mobility Among Wifi Access Points, Minkyong Kim, David Kotz

Dartmouth Scholarship

Modeling movements of users is important for simulating wireless networks, but current models often do not reflect real movements. Using real mobility traces, we can build a mobility model that reflects reality. In building a mobility model, it is important to note that while the number of handheld wireless devices is constantly increasing, laptops are still the majority in most cases. As a laptop is often disconnected from the network while a user is moving, it is not feasible to extract the exact path of the user from network messages. Thus, instead of modeling individual user's movements, we model movements …

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Analysis Of A Wi-Fi Hotspot Network, David P. Blinn, Tristan Henderson, David Kotz Jun 2005

Analysis Of A Wi-Fi Hotspot Network, David P. Blinn, Tristan Henderson, David Kotz

Dartmouth Scholarship

Wireless hotspot networks have become increasingly popular in recent years as a means of providing Internet access in public areas such as restaurants and airports. In this paper we present the first study of such a hotspot network. We examine five weeks of SNMP traces from the Verizon Wi-Fi HotSpot network in Manhattan. We find that far more cards associated to the network than logged into it. Most clients used the network infrequently and visited few APs. AP utilization was uneven and the network displayed some unusual patterns in traffic load. Some characteristics were similar to those previously observed in …

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A Toy Rock Climbing Robot, Matthew P. Bell May 2005

A Toy Rock Climbing Robot, Matthew P. Bell

Dartmouth College Undergraduate Theses

The goal of this thesis was to build a simple toy rock climbing robot, and to explore problems related to grasping, path planning, and robot control. The robot is capable of climbing a wall of pegs either under manual control through a host system and an infrared interface, or on the basis of a set of pre-recorded keyframes. In addition, the robot can climb certain peg configurations using a cyclic gait. The robot climbs in an open-loop mode without sensor feedback. All communications are sent through the IR connection, and the tether to the robot consists only of two power …

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Preventing Theft Of Quality Of Service On Open Platforms, Kwang-Hyun Baek, Sean W. Smith May 2005

Preventing Theft Of Quality Of Service On Open Platforms, Kwang-Hyun Baek, Sean W. Smith

Computer Science Technical Reports

As multiple types of traffic converge onto one network (frequently wireless), enterprises face a tradeoff between effectiveness and security. Some types of traffic, such as voice-over-IP (VoIP), require certain quality of service (QoS) guarantees to be effective. The end client platform is in the best position to know which packets deserve this special handling. In many environments (such as universities), end users relish having control over their own machines. However, if end users administer their own machines, nothing stops dishonest ones from marking undeserving traffic for high QoS. How can an enterprise ensure that only appropriate traffic receives high QoS, …

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Aggregated Path Authentication For Efficient Bgp Security, Meiyuan Zhao, Sean W. Smith, David M. Nicol May 2005

Aggregated Path Authentication For Efficient Bgp Security, Meiyuan Zhao, Sean W. Smith, David M. Nicol

Computer Science Technical Reports

The border gateway protocol (BGP) controls inter-domain routing in the Internet. BGP is vulnerable to many attacks, since routers rely on hearsay information from neighbors. Secure BGP (S-BGP) uses DSA to provide route authentication and mitigate many of these risks. However, many performance and deployment issues prevent S-BGP's real-world deployment. Previous work has explored improving S-BGP processing latencies, but space problems, such as increased message size and memory cost, remain the major obstacles. In this paper, we combine two efficient cryptographic techniques---signature amortization and aggregate signatures---to design new aggregated path authentication schemes. We propose six constructions for aggregated path authentication …

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An O(N^{5/2} Log N) Algorithm For The Rectilinear Minimum Link-Distance Problem In Three Dimensions (Extended Abstract), Robert Scot Drysdale, Clifford Stein, David P. Wagner May 2005

An O(N^{5/2} Log N) Algorithm For The Rectilinear Minimum Link-Distance Problem In Three Dimensions (Extended Abstract), Robert Scot Drysdale, Clifford Stein, David P. Wagner

Computer Science Technical Reports

In this paper we consider the Rectilinear Minimum Link-Distance Problem in Three Dimensions. The problem is well studied in two dimensions, but is relatively unexplored in higher dimensions. We solve the problem in O(B n log n) time, where n is the number of corners among all obstacles, and B is the size of a BSP decomposition of the space containing the obstacles. It has been shown that in the worst case B = Theta(n^{3/2}), giving us an overall worst case time of O(n^{5/2} log n). Previously known algorithms have had worst-case running times of Omega(n^3).

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Classifying The Mobility Of Users And The Popularity Of Access Points, Minkyong Kim, David Kotz May 2005

Classifying The Mobility Of Users And The Popularity Of Access Points, Minkyong Kim, David Kotz

Dartmouth Scholarship

There is increasing interest in location-aware systems and applications. It is important for any designer of such systems and applications to understand the nature of user and device mobility. Furthermore, an understanding of the effect of user mobility on access points (APs) is also important for designing, deploying, and managing wireless networks. Although various studies of wireless networks have provided insights into different network environments and user groups, it is often hard to apply these findings to other situations, or to derive useful abstract models. \par In this paper, we present a general methodology for extracting mobility information from wireless …

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Classifying The Mobility Of Users And The Popularity Of Access Points, Minkyong Kim, David Kotz May 2005

Classifying The Mobility Of Users And The Popularity Of Access Points, Minkyong Kim, David Kotz

Computer Science Technical Reports

There is increasing interest in location-aware systems and applications. It is important for any designer of such systems and applications to understand the nature of user and device mobility. Furthermore, an understanding of the effect of user mobility on access points (APs) is also important for designing, deploying, and managing wireless networks. Although various studies of wireless networks have provided insights into different network environments and user groups, it is often hard to apply these findings to other situations, or to derive useful abstract models. In this paper, we present a general methodology for extracting mobility information from wireless network …

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Measuring Wireless Network Usage With The Experience Sampling Method, Tristan Henderson, Denise Anthony, David Kotz Apr 2005

Measuring Wireless Network Usage With The Experience Sampling Method, Tristan Henderson, Denise Anthony, David Kotz

Dartmouth Scholarship

Measuring wireless local area networks has proven useful for characterizing, modeling and provisioning these networks. These measurements are typically taken passively from a vantage point on the network itself. Client devices, or users, are never actively queried. These measurements can indicate \em what is happening on the network, but it can be difficult to infer \em why a particular behavior is occurring. In this paper we use the Experience Sampling Method (ESM) to study wireless network users. We monitored 29 users remotely for one week, and signaled them to fill out a questionnaire whenever interesting wireless behavior was observed. We …

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Department Of Computer Science Activity 1998-2004, David Kotz Mar 2005

Department Of Computer Science Activity 1998-2004, David Kotz

Computer Science Technical Reports

This report summarizes much of the research and teaching activity of the Department of Computer Science at Dartmouth College between late 1998 and late 2004. The material for this report was collected as part of the final report for NSF Institutional Infrastructure award EIA-9802068, which funded equipment and technical staff during that six-year period. This equipment and staff supported essentially all of the department's research activity during that period.

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Secure Context-Sensitive Authorization, Kazuhiro Minami, David Kotz Mar 2005

Secure Context-Sensitive Authorization, Kazuhiro Minami, David Kotz

Dartmouth Scholarship

There is a recent trend toward rule-based authorization systems to achieve flexible security policies. Also, new sensing technologies in pervasive computing make it possible to define context-sensitive rules, such as “allow database access only to staff who are currently located in the main office.” However, these rules, or the facts that are needed to verify authority, often involve sensitive context information. This paper presents a secure context-sensitive authorization system that protects confidential information in facts or rules. Furthermore, our system allows multiple hosts in a distributed environment to perform the evaluation of an authorization query in a collaborative way; we …

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Graphical Models Of Residue Coupling In Protein Families, John Thomas, Naren Ramakrishnan, Chris Bailey-Kellogg Mar 2005

Graphical Models Of Residue Coupling In Protein Families, John Thomas, Naren Ramakrishnan, Chris Bailey-Kellogg

Computer Science Technical Reports

Identifying residue coupling relationships within a protein family can provide important insights into intrinsic molecular processes, and has significant applications in modeling structure and dynamics, understanding function, and designing new or modified proteins. We present the first algorithm to infer an undirected graphical model representing residue coupling in protein families. Such a model serves as a compact description of the joint amino acid distribution, and can be used for predictive (will this newly designed protein be folded and functional?), diagnostic (why is this protein not stable or functional?), and abductive reasoning (what if I attempt to graft features of one …

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Secure Context-Sensitive Authorization, Kazuhiro Minami, David Kotz Mar 2005

Secure Context-Sensitive Authorization, Kazuhiro Minami, David Kotz

Dartmouth Scholarship

There is a recent trend toward rule-based authorization systems to achieve flexible security policies. Also, new sensing technologies in pervasive computing make it possible to define context-sensitive rules, such as “allow database access only to staff who are currently located in the main office.” However, these rules, or the facts that are needed to verify authority, often involve sensitive context information. This paper presents a secure context-sensitive authorization system that protects confidential information in facts or rules. Furthermore, our system allows multiple hosts in a distributed environment to perform the evaluation of an authorization query in a collaborative way; we …

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Policy-Driven Data Dissemination For Context-Aware Applications, Guanling Chen, David Kotz Mar 2005

Policy-Driven Data Dissemination For Context-Aware Applications, Guanling Chen, David Kotz

Dartmouth Scholarship

Context-aware pervasive-computing applications require continuous monitoring of their physical and computational environment to make appropriate adaptation decisions in time. The data streams produced by sensors, however, may overflow the queues on the dissemination path. Traditional flow-control and congestion-control policies either drop data or force the sender to pause. When the data sender is sensing the physical environment, however, a pause is equivalent to dropping data. Instead of arbitrarily dropping data that may contain important events, we present a policy-driven data dissemination service named PACK, based on an overlay-based infrastructure for efficient multicast delivery. PACK enforces application-specified policies that define how …

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Shemp: Secure Hardware Enhanced Myproxy, John Marchesini, Sean Smith Feb 2005

Shemp: Secure Hardware Enhanced Myproxy, John Marchesini, Sean Smith

Computer Science Technical Reports

While PKI applications differ in how they use keys, all applications share one assumption: users have keypairs. In previous work, we established that desktop keystores are not safe places to store private keys, because the TCB is too large. These keystores are also immobile, difficult to use, and make it impossible for relying parties to make reasonable trust judgments. Since we would like to use desktops as PKI clients and cannot realistically expect to redesign the entire desktop, this paper presents a system that works within the confines of modern desktops to shrink the TCB needed for PKI applications. Our …

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High-Throughput Inference Of Protein-Protein Interaction Sites From Unassigned Nmr Data By Analyzing Arrangements Induced By Quadratic Forms On 3-Manifolds, Ramgopal R. Mettu, Ryan H. Lilien, Bruce Randall Donald Jan 2005

High-Throughput Inference Of Protein-Protein Interaction Sites From Unassigned Nmr Data By Analyzing Arrangements Induced By Quadratic Forms On 3-Manifolds, Ramgopal R. Mettu, Ryan H. Lilien, Bruce Randall Donald

Computer Science Technical Reports

We cast the problem of identifying protein-protein interfaces, using only unassigned NMR spectra, into a geometric clustering problem. Identifying protein-protein interfaces is critical to understanding inter- and intra-cellular communication, and NMR allows the study of protein interaction in solution. However it is often the case that NMR studies of a protein complex are very time-consuming, mainly due to the bottleneck in assigning the chemical shifts, even if the apo structures of the constituent proteins are known. We study whether it is possible, in a high-throughput manner, to identify the interface region of a protein complex using only unassigned chemical shift …

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The Kerf Toolkit For Intrusion Analysis, Javed Aslam, Sergey Bratus, David Kotz, Ronald Peterson Jan 2005

The Kerf Toolkit For Intrusion Analysis, Javed Aslam, Sergey Bratus, David Kotz, Ronald Peterson

Dartmouth Scholarship

No abstract provided.

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Secure Context-Sensitive Authorization, Kazuhiro Minami, David Kotz Dec 2004

Secure Context-Sensitive Authorization, Kazuhiro Minami, David Kotz

Computer Science Technical Reports

There is a recent trend toward rule-based authorization systems to achieve flexible security policies. Also, new sensing technologies in pervasive computing make it possible to define context-sensitive rules, such as ``allow database access only to staff who are currently located in the main office.'' However, these rules, or the facts that are needed to verify authority, often involve sensitive context information. This paper presents a secure context-sensitive authorization system that protects confidential information in facts or rules. Furthermore, our system allows multiple hosts in a distributed environment to perform the evaluation of an authorization query in a collaborative way; we …

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Discrete-Time Fractional Differentiation From Integer Derivatives, Hany Farid Dec 2004

Discrete-Time Fractional Differentiation From Integer Derivatives, Hany Farid

Computer Science Technical Reports

Discrete-time fractional derivative filters (1-D and 2-D) are shown to be well approximated from a small set of integer derivatives. A fractional derivative of arbitrary order (and, in 2-D, of arbitrary orientation) can therefore be efficiently computed from a linear combination of integer derivatives of the underlying signal or image.

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Statistical Tools For Digital Image Forensics, Alin C. Popescu Dec 2004

Statistical Tools For Digital Image Forensics, Alin C. Popescu

Dartmouth College Ph.D Dissertations

A digitally altered image, often leaving no visual clues of having been tampered with, can be indistinguishable from an authentic image. The tampering, however, may disturb some underlying statistical properties of the image. Under this assumption, we propose five techniques that quantify and detect statistical perturbations found in different forms of tampered images: (1) re-sampled images (e.g., scaled or rotated); (2) manipulated color filter array interpolated images; (3) double JPEG compressed images; (4) images with duplicated regions; and (5) images with inconsistent noise patterns. These techniques work in the absence of any embedded watermarks or signatures. For each technique we …

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Secure Hardware Enhanced Myproxy: A Ph.D. Thesis Proposal, John Marchesini, Sean Smith Nov 2004

Secure Hardware Enhanced Myproxy: A Ph.D. Thesis Proposal, John Marchesini, Sean Smith

Computer Science Technical Reports

In 1976, Whitfield Diffie and Martin Hellman demonstrated how "New Directions In Cryptography" could enable secure information exchange between parties that do not share secrets. In order for public key cryptography to work in modern distributed environments, we need an infrastructure for finding and trusting other parties' public keys (i.e., a PKI). A number of useful applications become possible with PKI. While the applications differ in how they use keys (e.g., S/MIME uses the key for message encryption and signing, while client-side SSL uses the key for authentication), all applications share one assumption: users have keypairs. In previous work, we …

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A Survey Of Wpa And 802.11i Rsn Authentication Protocols, Kwang-Hyun Baek, Sean W. Smith, David Kotz Nov 2004

A Survey Of Wpa And 802.11i Rsn Authentication Protocols, Kwang-Hyun Baek, Sean W. Smith, David Kotz

Computer Science Technical Reports

In the new standards for WLAN security, many choices exist for the authentication process. In this paper, we list eight desired properties of WLAN authentication protocols, survey eight recent authentication protocols, and analyze the protocols according to the desired properties.

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Problems With The Dartmouth Wireless Snmp Data Collection, Tristan Henderson, David Kotz Oct 2004

Problems With The Dartmouth Wireless Snmp Data Collection, Tristan Henderson, David Kotz

Computer Science Technical Reports

The original Dartmouth wireless network study used SNMP to query the college's Cisco 802.11b access points. The perl scripts that performed the SNMP queries suffered from some problems, in that they queried inappropriate SNMP values, or misunderstood the meaning of other values. This data was also used in a subsequent analysis. The same scripts were used to collect data for a subsequent study of another wireless network. This document outlines these problems and indicates which of the data collected by the original scripts may be invalid.

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Composing A Well-Typed Region, Chris Hawblitzel, Heng Huang, Lea Wittie Oct 2004

Composing A Well-Typed Region, Chris Hawblitzel, Heng Huang, Lea Wittie

Computer Science Technical Reports

Efficient low-level systems need more control over memory than safe high-level languages usually provide. In particular, safe languages usually prohibit explicit deallocation, in order to prevent dangling pointers. Regions provide one safe deallocation mechanism; indeed, many region calculi have appeared recently, each with its own set of operations and often complex rules. This paper encodes regions from lower-level typed primitives (linear memory, coercions, and delayed types), so that programmers can design their own region operations and rules.

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Performance Evaluation Of A Resource Discovery Service, Jue Wang Oct 2004

Performance Evaluation Of A Resource Discovery Service, Jue Wang

Dartmouth College Master’s Theses

In a pervasive computing environment, the number and variety of resources (services, devices, and contextual information resources) make it necessary for applications to accurately discover the best ones quickly. Thus a resource-discovery service, which locates specific resources and establishes network connections as better resources become available, is necessary for those applications. The performance of the resource-discovery service is important when the applications are in a dynamic and mobile environment. In this thesis, however, we do not focus on the resource- discovery technology itself, but the evaluation of the scalability and mobility of the resource discovery module in Solar, a context …

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Automatic Image Orientation Determination With Natural Image Statistics, Siwei Lyu Oct 2004

Automatic Image Orientation Determination With Natural Image Statistics, Siwei Lyu

Computer Science Technical Reports

In this paper, we propose a new method for automatically determining image orientations. This method is based on a set of natural image statistics collected from a multi-scale multi-orientation image decomposition (e.g., wavelets). From these statistics, a two-stage hierarchal classification with multiple binary SVM classifiers is employed to de- termine image orientation. The proposed method is evaluated and compared to existing methods with experiments performed on 18040 natural images, where it showed promising performance.

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