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Full-Text Articles in Computer Sciences

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 …


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.


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

Secure Hardware Enhanced Myproxy: A Ph.D. Thesis Proposal, John Marchesini, David Kotz

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 …


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.


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.


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.


Mercer Kernels For Object Recognition With Local Features, Siwei Lyu Oct 2004

Mercer Kernels For Object Recognition With Local Features, Siwei Lyu

Computer Science Technical Reports

In this paper, we propose a new class of kernels for object recognition based on local image feature representations. Formal proofs are given to show that these kernels satisfy the Mercer condition and reflect similarities between sets of local features. In addition, multiple types of local features and semilocal constraints are incorporated to reduce mismatches between local features, thus further improve the classification performance. Experimental results of SVM classifiers coupled with the proposed kernels are reported on ecognition tasks with the standard COIL-100 database and compared with existing methods. The proposed kernels achieved satisfactory performance and were robust to changes …


Efficient Wait-Free Implementation Of Multiword Ll/Sc Variables, Prasad Jayanti, Srdjan Petrovic Oct 2004

Efficient Wait-Free Implementation Of Multiword Ll/Sc Variables, Prasad Jayanti, Srdjan Petrovic

Computer Science Technical Reports

Since the design of lock-free data structures often poses a formidable intellectual challenge, researchers are constantly in search of abstractions and primitives that simplify this design. The multiword LL/SC object is such a primitive: many existing algorithms are based on this primitive, including the nonblocking and wait-free universal constructions of Anderson and Moir (1995), the closed objects construction of Chandra et al.(1998) and the snapshot algorithms of Jayanti (2002, 2004). In this paper, we consider the problem of implementing a W-word LL/SC object shared by N processes. The previous best algorithm, due to Anderson and Moir (1995), is time optimal …


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.


Experimental Evaluation Of Wireless Simulation Assumptions, David Kotz, Calvin Newport, Robert S. Gray, Jason Liu, Yougu Yuan, Chip Elliot Oct 2004

Experimental Evaluation Of Wireless Simulation Assumptions, David Kotz, Calvin Newport, Robert S. Gray, Jason Liu, Yougu Yuan, Chip Elliot

Dartmouth Scholarship

All analytical and simulation research on ad hoc wireless networks must necessarily model radio propagation using simplifying assumptions. We provide a comprehensive review of six assumptions that are still part of many ad hoc network simulation studies, despite increasing awareness of the need to represent more realistic features, including hills, obstacles, link asymmetries, and unpredictable fading. We use an extensive set of measurements from a large outdoor routing experiment to demonstrate the weakness of these assumptions, and show how these assumptions cause simulation results to differ significantly from experimental results. We close with a series of recommendations for researchers, whether …


Creating And Detecting Doctored And Virtual Images: Implications To The Child Pornography Prevention Act, Hany Farid Sep 2004

Creating And Detecting Doctored And Virtual Images: Implications To The Child Pornography Prevention Act, Hany Farid

Computer Science Technical Reports

The 1996 Child Pornography Prevention Act (CPPA) extended the existing federal criminal laws against child pornography to include certain types of "virtual porn". In 2002, the United States Supreme Court found that portions of the CPPA, being overly broad and restrictive, violated First Amendment rights. The Court ruled that images containing an actual minor or portions of a minor are not protected, while computer generated images depicting a fictitious "computer generated" minor are constitutionally protected. In this report I outline various forms of digital tampering, placing them in the context of this recent ruling. I also review computational techniques for …


The Changing Usage Of A Mature Campus-Wide Wireless Network, Tristan Henderson, David Kotz, Ilya Abyzov Sep 2004

The Changing Usage Of A Mature Campus-Wide Wireless Network, Tristan Henderson, David Kotz, Ilya Abyzov

Dartmouth Scholarship

Wireless Local Area Networks (WLANs) are now commonplace on many academic and corporate campuses. As “Wi-Fi” technology becomes ubiquitous, it is increasingly important to understand trends in the usage of these networks. \par This paper analyzes an extensive network trace from a mature 802.11 WLAN, including more than 550 access points and 7000 users over seventeen weeks. We employ several measurement techniques, including syslogs, telephone records, SNMP polling and tcpdump packet sniffing. This is the largest WLAN study to date, and the first to look at a large, mature WLAN and consider geographic mobility. We compare this trace to a …


Exposing Digital Forgeries By Detecting Duplicated Image Regions, Alin C. Popescu, Hany Farid Aug 2004

Exposing Digital Forgeries By Detecting Duplicated Image Regions, Alin C. Popescu, Hany Farid

Computer Science Technical Reports

We describe an efficient technique that automatically detects duplicated regions in a digital image. This technique works by first applying a principal component analysis to small fixed-size image blocks to yield a reduced dimension representation. This representation is robust to minor variations in the image due to additive noise or lossy compression. Duplicated regions are then detected by lexicographically sorting all of the image blocks. We show the efficacy of this technique on credible forgeries, and quantify its robustness and sensitivity to additive noise and lossy JPEG compression.


Design And Implementation Of A Large-Scale Context Fusion Network, Guanling Chen, Ming Li, David Kotz Aug 2004

Design And Implementation Of A Large-Scale Context Fusion Network, Guanling Chen, Ming Li, David Kotz

Dartmouth Scholarship

In this paper we motivate a Context Fusion Network (CFN), an infrastructure model that allows context-aware applications to select distributed data sources and compose them with customized data-fusion operators into a directed acyclic information fusion graph. Such a graph represents how an application computes high-level understandings of its execution context from low-level sensory data. Multiple graphs by different applications inter-connect with each other to form a global graph. A key advantage of a CFN is re-usability, both at code-level and instance-level, facilitated by operator composition. We designed and implemented a distributed CFN system, Solar, which maps the logical operator graph …


Kerf: Machine Learning To Aid Intrusion Analysts, Javed Aslam, Sergey Bratus, David Kotz, Ron Peterson, Daniela Rus Aug 2004

Kerf: Machine Learning To Aid Intrusion Analysts, Javed Aslam, Sergey Bratus, David Kotz, Ron Peterson, Daniela Rus

Dartmouth Scholarship

Kerf is a toolkit for post-hoc intrusion analysis of available system logs and some types of network logs. It takes the view that this process is inherently interactive and iterative: the human analyst browses the log data for apparent anomalies, and tests and revises his hypothesis of what happened. The hypothesis is alternately refined, as information that partially confirms the hypothesis is discovered, and expanded, as the analyst tries new avenues that broaden the investigation.


Probabilistic Disease Classification Of Expression-Dependent Proteomic Data From Mass Spectrometry Of Human Serum, Ryan H. Lilien, Hany Farid, Bruce R. Donald Jul 2004

Probabilistic Disease Classification Of Expression-Dependent Proteomic Data From Mass Spectrometry Of Human Serum, Ryan H. Lilien, Hany Farid, Bruce R. Donald

Dartmouth Scholarship

We have developed an algorithm called Q5 for probabilistic classification of healthy vs. disease whole serum samples using mass spectrometry. The algorithm employs Principal Components Analysis (PCA) followed by Linear Discriminant Analysis (LDA) on whole spectrum Surface-Enhanced Laser Desorption/Ionization Time of Flight (SELDI-TOF) Mass Spectrometry (MS) data, and is demonstrated on four real datasets from complete, complex SELDI spectra of human blood serum.

Q5 is a closed-form, exact solution to the problem of classification of complete mass spectra of a complex protein mixture. Q5 employs a novel probabilistic classification algorithm built upon a dimension-reduced linear discriminant analysis. Our solution is …


Outdoor Experimental Comparison Of Four Ad Hoc Routing Algorithms, Robert S. Gray, David Kotz, Calvin Newport, Nikita Dubrovsky, Aaron Fiske, Jason Liu, Christopher Masone, Susan Mcgrath, Yougu Yuan Jun 2004

Outdoor Experimental Comparison Of Four Ad Hoc Routing Algorithms, Robert S. Gray, David Kotz, Calvin Newport, Nikita Dubrovsky, Aaron Fiske, Jason Liu, Christopher Masone, Susan Mcgrath, Yougu Yuan

Computer Science Technical Reports

Most comparisons of wireless ad hoc routing algorithms involve simulated or indoor trial runs, or outdoor runs with only a small number of nodes, potentially leading to an incorrect picture of algorithm performance. In this paper, we report on the results of an outdoor trial run of four different routing algorithms, APRL, AODV, GPSR, and STARA, running on top of thirty-three 802.11-enabled laptops moving randomly through an athletic field. The laptops generated random traffic according to the traffic patterns observed in a prototype application, and ran each routing algorithm for a fifteen-minute period over the course of the hour-long trial …


Experimental Evaluation Of Wireless Simulation Assumptions, David Kotz, Calvin Newport, Robert S. Gray, Jason Liu, Yougu Yuan, Chip Elliott Jun 2004

Experimental Evaluation Of Wireless Simulation Assumptions, David Kotz, Calvin Newport, Robert S. Gray, Jason Liu, Yougu Yuan, Chip Elliott

Computer Science Technical Reports

All analytical and simulation research on ad~hoc wireless networks must necessarily model radio propagation using simplifying assumptions. Although it is tempting to assume that all radios have circular range, have perfect coverage in that range, and travel on a two-dimensional plane, most researchers are increasingly aware of the need to represent more realistic features, including hills, obstacles, link asymmetries, and unpredictable fading. Although many have noted the complexity of real radio propagation, and some have quantified the effect of overly simple assumptions on the simulation of ad~hoc network protocols, we provide a comprehensive review of six assumptions that are still …


Technological Implications For Privacy, David Kotz Jun 2004

Technological Implications For Privacy, David Kotz

Computer Science Technical Reports

The World-Wide Web is increasingly used for commerce and access to personal information stored in databases. Although the Web is ``just another medium'' for information exchange, the fact that all the information is stored in computers, and all of the activity happens in computers and computer networks, makes it easier (cheaper) than every to track users' activities. By recording and analyzing user's activities in the Web, activities that may seem to be quite private to many users, it is more likely than ever before that a person's privacy may be threatened. In this paper I examine some of the technology …


A Sensor-Fusion Approach For Meeting Detection, Jue Wang, Guanling Chen, David Kotz Jun 2004

A Sensor-Fusion Approach For Meeting Detection, Jue Wang, Guanling Chen, David Kotz

Dartmouth Scholarship

In this paper we present a context-sensing component that recognizes meetings in a typical office environment. Our prototype detects the meeting start and end by combining outputs from pressure and motion sensors installed on the chairs. We developed a telephone controller application that transfers incoming calls to voice-mail when the user is in a meeting. Our experiments show that it is feasible to detect high-level context changes with “good enough” accuracy, using low-cost, off-the-shelf hardware, and simple algorithms without complex training. We also note the need for better metrics to measure context detection performance, other than just accuracy. We propose …


A Sensor Fusion Approach For Meeting Detection, Jue Wang, Guanling Chen, David Kotz Jun 2004

A Sensor Fusion Approach For Meeting Detection, Jue Wang, Guanling Chen, David Kotz

Dartmouth Scholarship

In this paper we present a context-sensing component that recognizes meetings in a typical office environment. Our prototype detects the meeting start and end by combining outputs from pressure and motion sensors installed on the chairs. We developed a telephone controller application that transfers incoming calls to voice-mail when the user is in a meeting. Our experiments show that it is feasible to detect high-level context changes with ``good enough'' accuracy, using low-cost, off-the-shelf hardware, and simple algorithms without complex training. We also note the need for better metrics to measure context detection performance, other than just accuracy. We propose …


A Holesome File System, Darren Erik Vengroff, David Kotz May 2004

A Holesome File System, Darren Erik Vengroff, David Kotz

Computer Science Technical Reports

We present a novel approach to fully dynamic management of physical disk blocks in Unix file systems. By adding a single system call, zero, to an existing file system, we permit applications to create holes, that is, regions of files to which no physical disk blocks are allocated, far more flexibly than previously possible. zero can create holes in the middle of existing files. Using zero, it is possible to efficiently implement applications including a variety of databases and I/O-efficient computation systems on top of the Unix file system. zero can also be used to implement an efficient file-system-based paging …


Dependency Management In Distributed Settings (Poster Abstract), Guanling Chen, David Kotz May 2004

Dependency Management In Distributed Settings (Poster Abstract), Guanling Chen, David Kotz

Dartmouth Scholarship

Ubiquitous-computing environments are heterogeneous and volatile in nature. Systems that support ubicomp applications must be self-managed, to reduce human intervention. In this paper, we present a general service that helps distributed software components to manage their dependencies. Our service proactively monitors the liveness of components and recovers them according to supplied policies. Our service also tracks the state of components, on behalf of their dependents, and may automatically select components for the dependent to use based on evaluations of customized functions. We believe that our approach is flexible and abstracts away many of the complexities encountered in ubicomp environments. In …


Simulation Validation Using Direct Execution Of Wireless Ad-Hoc Routing Protocols, Jason Liu, Yougu Yuan, David M. Nicol, Robert S. Gray, Calvin C. Newport, David Kotz, Luiz Felipe Perrone May 2004

Simulation Validation Using Direct Execution Of Wireless Ad-Hoc Routing Protocols, Jason Liu, Yougu Yuan, David M. Nicol, Robert S. Gray, Calvin C. Newport, David Kotz, Luiz Felipe Perrone

Dartmouth Scholarship

Computer simulation is the most common approach to studying wireless ad-hoc routing algorithms. The results, however, are only as good as the models the simulation uses. One should not underestimate the importance of \em validation, as inaccurate models can lead to wrong conclusions. In this paper, we use direct-execution simulation to validate radio models used by ad-hoc routing protocols, against real-world experiments. This paper documents a common testbed that supports direct execution of a set of ad-hoc routing protocol implementations in a wireless network simulator. The testbed reads traces generated from real experiments, and uses them to drive direct-execution implementations …


The Kerf Toolkit For Intrusion Analysis, Javed Aslam, Sergey Bratus, David Kotz, Ron Peterson, Daniela Rus, Brett Tofel Mar 2004

The Kerf Toolkit For Intrusion Analysis, Javed Aslam, Sergey Bratus, David Kotz, Ron Peterson, Daniela Rus, Brett Tofel

Computer Science Technical Reports

We consider the problem of intrusion analysis and present the Kerf Toolkit, whose purpose is to provide an efficient and flexible infrastructure for the analysis of attacks. The Kerf Toolkit includes a mechanism for securely recording host and network logging information for a network of workstations, a domain-specific language for querying this stored data, and an interface for viewing the results of such a query, providing feedback on these results, and generating new queries in an iterative fashion. We describe the architecture of Kerf, present examples to demonstrate the power of our query language, and discuss the performance of our …


A Subgroup Algorithm To Identify Cross-Rotation Peaks Consistent With Non-Crystallographic Symmetry, Ryan H. Lilien, Chris Bailey-Kellogg, Amy C. Anderson, Bruce R. Donald Mar 2004

A Subgroup Algorithm To Identify Cross-Rotation Peaks Consistent With Non-Crystallographic Symmetry, Ryan H. Lilien, Chris Bailey-Kellogg, Amy C. Anderson, Bruce R. Donald

Dartmouth Scholarship

Molecular replacement (MR) often plays a prominent role in determining initial phase angles for structure determination by X-ray crystallography. In this paper, an efficient quaternion-based algorithm is presented for analyzing peaks from a cross-rotation function in order to identify model orientations consistent with proper non-crystallographic symmetry (NCS) and to generate proper NCS-consistent orientations missing from the list of cross-rotation peaks. The algorithm, CRANS, analyzes the rotation differences between each pair of cross-rotation peaks to identify finite subgroups. Sets of rotation differences satisfying the subgroup axioms correspond to orientations compatible with the correct proper NCS. The CRANS algorithm was first …


The Changing Usage Of A Mature Campus-Wide Wireless Network, Tristan Henderson, David Kotz, Ilya Abyzov Mar 2004

The Changing Usage Of A Mature Campus-Wide Wireless Network, Tristan Henderson, David Kotz, Ilya Abyzov

Computer Science Technical Reports

Wireless Local Area Networks (WLANs) are now common on academic and corporate campuses. As ``Wi-Fi'' technology becomes ubiquitous, it is increasingly important to understand trends in the usage of these networks. This paper analyzes an extensive network trace from a mature 802.11 WLAN, including more than 550 access points and 7000 users over seventeen weeks. We employ several measurement techniques, including syslogs, telephone records, SNMP polling and tcpdump packet sniffing. This is the largest WLAN study to date, and the first to look at a large, mature WLAN and consider geographic mobility. We compare this trace to a trace taken …


Identification Of Novel Small Molecule Inhibitors Of Core-Binding Factor Dimerization By Computational Screening Against Nmr Molecular Ensemble, Ryan H. Lilien, Mohini Sridharan, Bruce R. Donald Mar 2004

Identification Of Novel Small Molecule Inhibitors Of Core-Binding Factor Dimerization By Computational Screening Against Nmr Molecular Ensemble, Ryan H. Lilien, Mohini Sridharan, Bruce R. Donald

Computer Science Technical Reports

The long development process of novel pharmaceutical compounds begins with the identification of a lead inhibitor compound. Computational screening to identify those ligands, or small molecules, most likely to inhibit a target protein may benefit the pharmaceutical development process by reducing the time required to identify a lead compound. Typically, computational ligand screening utilizes high-resolution structural models of both the protein and ligand to fit or `dock' each member of a ligand database into the binding site of the protein. Ligands are then ranked by the number and quality of interactions formed in the predicted protein-ligand complex. It is currently …


A Meeting Detector And Its Applications, Jue Wang, Guanling Chen, David Kotz Mar 2004

A Meeting Detector And Its Applications, Jue Wang, Guanling Chen, David Kotz

Computer Science Technical Reports

In this paper we present a context-sensing component that recognizes meetings in a typical office environment. Our prototype detects the meeting start and end by combining outputs from pressure and motion sensors installed on the chairs. We developed a telephone controller application that transfers incoming calls to voice-mail when the user is in a meeting. Our experiments show that it is feasible to detect high-level context changes with ``good enough'' accuracy, using low-cost, off-the-shelf hardware, and simple algorithms without complex training. We also note the need for better metrics to measure context detection performance, other than just accuracy. We propose …


Dependency Management In Distributed Settings, Guanling Chen, David Kotz Mar 2004

Dependency Management In Distributed Settings, Guanling Chen, David Kotz

Computer Science Technical Reports

Ubiquitous-computing environments are heterogeneous and volatile in nature. Systems that support ubicomp applications must be self-managed, to reduce human intervention. In this paper, we present a general service that helps distributed software components to manage their dependencies. Our service proactively monitors the liveness of components and recovers them according to supplied policies. Our service also tracks the state of components, on behalf of their dependents, and may automatically select components for the dependent to use based on evaluations of customized functions. We believe that our approach is flexible and abstracts away many of the complexities encountered in ubicomp environments. In …