Physical Sciences and Mathematics Commons^™

Proofs Of Soundness And Strong Normalization For Linear Memory Types, Heng Huang, Chris Hawblitzel

Computer Science Technical Reports

Efficient low-level systems need more control over memory than safe high-level languages usually provide. As a result, run-time systems are typically written in unsafe languages such as C. This report describes an abstract machine designed to give type-safe code more control over memory. It includes complete definitions and proofs.

Exact Formulae For The Lovasz Theta Function Of Sparse Circulant Graphs, Valentino Crespi

Computer Science Technical Reports

The Lovasz theta function has attracted a lot of attention for its connection with diverse issues, such as communicating without errors and computing large cliques in graphs. Indeed this function enjoys the remarkable property of being computable in polynomial time, despite being sandwitched between clique and chromatic number, two well known hard to compute quantities. In this paper I provide a closed formula for the Lovasz function of a specific class of sparse circulant graphs thus generalizing Lovasz results on cycle graphs (circulant graphs of degree 2).

Toward Dynamic Interoperability Of Mobile Agent Systems, Arne Grimstrup, Robert Gray, David Kotz, Maggie Breedy, Marco Carvalho, Thomas Cowin, Daria Chacon, Joyce Barton, Chris Garrett, Martin Hofmann

Dartmouth Scholarship

Mobile agents are an increasingly popular paradigm and in recent years there has been a proliferation of mobile-agent systems. These systems are, however, largely incompatible with each other. In particular, agents cannot migrate to a host that runs a different mobile-agent system. Prior approaches to interoperability have tried to force agents to use a common API and so far none have succeeded. This goal led to our efforts to develop mechanisms that support dynamic runtime interoperability of mobile-agent systems. This paper describes the \em Grid Mobile-Agent System, which allows agents to migrate to different mobile-agent systems.

Distributed Algorithms For Guiding Navigation Across A Sensor Network, Qun Li, Michael Derosa, Daniela Rus

Computer Science Technical Reports

We develop distributed algorithms for self-reconfiguring sensor networks that respond to directing a target through a region. The sensor network models the danger levels sensed across its area and has the ability to adapt to changes. It represents the dangerous areas as obstacles. A protocol that combines the artificial potential field of the sensors with the goal location for the moving object guides the object incrementally across the network to the goal, while maintaining the safest distance to the danger areas. We report on hardware experiments using a physical sensor network consisting of Mote sensors.

Using The Emulab Network Testbed To Evaluate The Armada I/O Framework For Computational Grids, Ron Oldfield, David Kotz

Computer Science Technical Reports

This short report describes our experiences using the Emulab network testbed at the University of Utah to test performance of the Armada framework for parallel I/O on computational grids.

Heterogeneous Self-Reconfiguring Robotics: Ph.D. Thesis Proposal, Robert C. Fitch

Computer Science Technical Reports

Self-reconfiguring robots are modular systems that can change shape, or "reconfigure," to match structure to task. They comprise many small, discrete, often identical modules that connect together and that are minimally actuated. Global shape transformation is achieved by composing local motions. Systems with a single module type, known as "homogeneous" systems, gain fault tolerance, robustness and low production cost from module interchangeability. However, we are interested in "heterogeneous" systems, which include multiple types of modules such as those with sensors, batteries or wheels. We believe that heterogeneous systems offer the same benefits as homogeneous systems with the added ability to …

Analysis Of A Campus-Wide Wireless Network, David Kotz, Kobby Essien

Computer Science Technical Reports

Understanding usage patterns in wireless local-area networks (WLANs) is critical for those who develop, deploy, and manage WLAN technology, as well as those who develop systems and application software for wireless networks. This paper presents results from the largest and most comprehensive trace of network activity in a large, production wireless LAN. For eleven weeks we traced the activity of nearly two thousand users drawn from a general campus population, using a campus-wide network of 476 access points spread over 161 buildings. Our study expands on those done by Tang and Baker, with a significantly larger and broader population. We …

Analysis Of A Campus-Wide Wireless Network, David Kotz, Kobby Essien

Dartmouth Scholarship

Understanding usage patterns in wireless local-area networks (WLANs) is critical for those who develop, deploy, and manage WLAN technology, as well as those who develop systems and application software for wireless networks. This paper presents results from the largest and most comprehensive trace of network activity in a large, production wireless LAN. For eleven weeks we traced the activity of nearly two thousand users drawn from a general campus population, using a campus-wide network of 476 access points spread over 161 buildings. Our study expands on those done by Tang and Baker, with a significantly larger and broader population. \par …

Future Directions For Mobile-Agent Research, David Kotz, Robert Gray, Daniela Rus

Dartmouth Scholarship

The field of mobile agents should shift its emphasis toward mobile code, in all its forms, rather than continue focusing on mobile agents. The development of modular components will help application designers take advantage of code mobility without having to rewrite their applications to fit in monolithic, mobile agent systems.

The Future Of Cryptography Under Quantum Computers, Marco A. Barreno

Dartmouth College Undergraduate Theses

Cryptography is an ancient art that has passed through many paradigms, from simple letter substitutions to polyalphabetic substitutions to rotor machines to digital encryption to public-key cryptosystems. With the possible advent of quantum computers and the strange behaviors they exhibit, a new paradigm shift in cryptography may be on the horizon. Quantum computers could hold the potential to render most modern encryption useless against a quantum-enabled adversary. The aim of this thesis is to characterize this convergence of cryptography and quantum computation. We provide definitions for cryptographic primitives that frame them in general terms with respect to complexity. We explore …

Three Power-Aware Routing Algorithms For Sensor Networks, Javed Aslam, Qun Li, Daniela Rus

Dartmouth Scholarship

This paper discusses online power‐aware routing in large wireless ad hoc networks (especially sensor networks) for applications in which the message sequence is not known. We seek to optimize the lifetime of the network. We show that online power‐aware routing does not have a constant competitive ratio to the off‐line optimal algorithm. We develop an approximation algorithm called max–min zP_min that has a good empirical competitive ratio. To ensure scalability, we introduce a second online algorithm for power‐aware routing. This hierarchical algorithm is called zone‐based routing. Our experiments show that its performance is quite good. Finally, we …

Performance And Interoperability In Solar, A Abram White

Dartmouth College Undergraduate Theses

Ubiquitous computing promises to integrate computers into our physical environment, surrounding us with applications that are able to adapt to our dynamics. Solar is a software infrastructure designed to deliver contextual information to these applications. To serve the large number and wide variety of context-aware devices envisioned by ubiquitous computing, Solar must exhibit both high performance and the ability to interoperate with many computing platforms. We created a testing framework to measure the performance of distributed systems such as Solar, as well as a pluggable data-transfer mechanism to support the dissemination of information to heterogeneous applications. This paper explores the …

Xslt And Xquery As Operator Languages, A Abram White

Computer Science Technical Reports

Ubiquitous computing promises to integrate computers into our physical environment, surrounding us with applications that are able to adapt to our dynamics. Solar is a software infrastructure designed to deliver contextual information to these applications. Solar represents context data as events, and uses small programs called operators to filter, merge, aggregate, or transform event streams. This paper explores the possibility of using XSLT and XQuery to build language-neutral Solar operators.

Solar: An Open Platform For Context-Aware Mobile Applications, Guanling Chen, David Kotz

Dartmouth Scholarship

Emerging pervasive computing technologies transform the way we live and work by embedding computation in our surrounding environment. To avoid increasing complexity, and allow the user to concentrate on her tasks, applications in a pervasive computing environment must automatically adapt to their changing \em context, including the user state and the physical and computational environment in which they run. Solar is a middleware platform to help these “context-aware” applications aggregate desired context from heterogeneous sources and to locate environmental services depending on the current context. By moving most of the context computation into the infrastructure, Solar allows applications to run …

Building Trusted Paths For Web Browsers, Zishuang (Eileen) Ye

Dartmouth College Master’s Theses

The communication between the Web browser and the human user is one component of the server-client channel. It is not the user but the browser that receives all server information and establishes the secure connection. The browser's user interface signals, such as SSL lock, https protocol header et al., indicate whether the browser-server communication at the current moment is secure. Those user interface signals indicating the security status of browser should be clearly and correctly understood by the user.

A survey of modern Web browsers shows the information provided by current browsers is insufficient for users to make trust judgment. …

Role Definition Language (Rdl): A Language To Describe Context-Aware Roles, Christopher P. Masone

Dartmouth College Undergraduate Theses

As wireless networks become more prevalent, a widening array of computational resources becomes available to the mobile user. Since not all users should have unrestricted access to these resources, a method of access control must be devised. In a context-aware environment, context information can be used to supplement more conventional password-based access control systems. We believe the best way to achieve this is through the use of Context-Aware Role-Based Access Control, a model in which permissions are assigned to entities called roles, each principal is a member of one or more roles, and a role's membership is determined using context …

Analysis Of Protein Sequences Using Time Frequency And Kolmogorov-Smirnov Methods, Kobby Essien

Dartmouth College Undergraduate Theses

The plethora of genomic data currently available has resulted in a search for new algorithms and analysis techniques to interpret genomic data. In this two-fold study we explore techniques for locating critical amino acid residues in protein sequences and for estimating the similarity between proteins. We demonstrate the use of the Short-Time Fourier Transform and the Continuous Wavelet Transform together with amino acid hydrophobicity in locating important amino acid domains in proteins and also show that the Kolmogorov-Smirnov statistic can be used as a metric of protein similarity.

Mobile Voice Over Ip (Mvoip): An Application-Level Protocol For Call Hand-Off In Real Time Applications, G. Ayorkor Mills-Tettey, David Kotz

Dartmouth Scholarship

This paper presents Mobile Voice Over IP, an application-level protocol to support terminal mobility in real-time applications such as voice over IP, on a wireless local area network. We describe our MVOIP implementation based on the ITU-T H.323 protocol stack, present experimental results on call hand-off latency, and discuss various implementation issues, including the task of quickly and accurately determining when call hand-off is necessary. We also discuss how MVOIP relates to other proposed mobility support schemes, and how it can be generalized to provide application-level mobility support in a wide range of real and non real-time applications.

Metasearch: Data Fusion For Document Retrieval, Mark H. Montague

Dartmouth College Ph.D Dissertations

The metasearch problem is to optimally merge the ranked lists output by an arbitrary number of search systems into one ranked list. In this work: (1) We show that metasearch improves upon not just the raw performance of the input search engines, but also upon the consistency of the input search engines from query to query. (2) We experimentally prove that simply weighting input systems by their average performance can dramatically improve fusion results. (3) We show that score normalization is an important component of a metasearch engine, and that dependence upon statistical outliers appears to be the problem with …

Characterizing Usage Of A Campus-Wide Wireless Network, David Kotz, Kobby Essien

Computer Science Technical Reports

Wireless local-area networks (WLANs) are increasingly common, but little is known about how they are used. A clear understanding of usage patterns in real WLANs is critical information to those who develop, deploy, and manage WLAN technology, as well as those who develop systems and application software for wireless networks. This paper presents results from the largest and most comprehensive trace of network activity in a large, production wireless LAN. For eleven weeks we traced the activity of nearly two thousand users drawn from a general campus population, using a campus-wide network of 476 access points spread over 161 buildings. …

Armada: A Parallel I/O Framework For Computational Grids, Ron Oldfield, David Kotz

Dartmouth Scholarship

High-performance computing increasingly occurs on “computational grids” composed of heterogeneous and geographically distributed systems of computers, networks, and storage devices that collectively act as a single “virtual” computer. One of the great challenges for this environment is to provide efficient access to data that is distributed across remote data servers in a grid. In this paper, we describe our solution, a framework we call Armada. Armada allows applications to flexibly compose modules to access their data, and to place those modules at appropriate hosts within the grid to reduce network traffic.

Controlling Access To Pervasive Information In The “Solar” System, Kazuhiro Minami, David Kotz

Computer Science Technical Reports

Pervasive-computing infrastructures necessarily collect a lot of context information to disseminate to their context-aware applications. Due to the personal or proprietary nature of much of this context information, however, the infrastructure must limit access to context information to authorized persons. In this paper we propose a new access-control mechanism for event-based context-distribution infrastructures. The core of our approach is based on a conservative information-flow model of access control, but users may express discretionary relaxation of the resulting access-control list (ACL) by specifying relaxation functions. This combination of automatic ACL derivation and user-specified ACL relaxation allows access control to be determined …

Context Aggregation And Dissemination In Ubiquitous Computing Systems, Guanling Chen, David Kotz

Computer Science Technical Reports

Many ``ubiquitous computing'' applications need a constant flow of information about their environment to be able to adapt to their changing context. To support these ``context-aware'' applications we propose a graph-based abstraction for collecting, aggregating, and disseminating context information. The abstraction models context information as events, produced by sources and flowing through a directed acyclic graph of event-processing operators and delivered to subscribing applications. Applications describe their desired event stream as a tree of operators that aggregate low-level context information published by existing sources into the high-level context information needed by the application. The operator graph is thus the dynamic …

Solar: A Pervasive-Computing Infrastructure For Context-Aware Mobile Applications, Guanling Chen, David Kotz

Computer Science Technical Reports

Emerging pervasive computing technologies transform the way we live and work by embedding computation in our surrounding environment. To avoid increasing complexity, and allow the user to concentrate on her tasks, applications must automatically adapt to their changing \emph{context}, the physical and computational environment in which they run. To support these ``context-aware'' applications we propose a graph-based abstraction for collecting, aggregating, and disseminating context information. The abstraction models context information as \emph{events}, which are produced by \emph{sources}, flow through a directed acyclic graph of event-processing \emph{operators}, and are delivered to subscribing applications. Applications describe their desired event stream as a …

Virtual Hierarchies - An Architecture For Building And Maintaining Efficient And Resilient Trust Chains, John Marchesini, Sean Smith

Computer Science Technical Reports

In Public Key Infrastructure (PKI), the simple, monopolistic CA model works fine until we consider the real world. Then, issues such as scalability and mutually suspicious organizations create the need for a multiplicity of CAs, which immediately introduces the problem of how to organize them to balance resilience to compromise against efficiency of path discovery. However, security has given us tools such as secure coprocessing, secret splitting, secret sharing, and threshold cryptography for securely carrying out computations among multiple trust domains; distributed computing has given us peer-to-peer networking, for creating self-organizing distributed systems. In this paper, we use these latter …

Trusted Paths For Browsers: An Open-Source Solution To Web Spoofing, Zishuang (Eileen) Ye, Sean Smith

Computer Science Technical Reports

The security of the vast majority of ``secure'' Web services rests on SSL server PKI. However, this PKI doesn't work if the the adversary can trick the browser into appearing to tell the user the wrong thing about the certificates and cryptography. The seminal web spoofing work of Felten et al demonstrated the potential, in 1996, for malicious servers to impersonate honest servers. Our recent follow-up work explicitly shows how malicious servers can still do this---and can also forge the existence of an SSL session and the contents of the alleged server certificate. This paper reports the results of our …

Ffts For The 2-Sphere - Improvements And Variations, D M. Healy Jr, D N. Rockmore, P J. Kostelec, Sean S.B. Moore

Computer Science Technical Reports

Earlier work by Driscoll and Healy has produced an efficient algorithm for computing the Fourier transform of band-limited functions on the 2-sphere. In this paper we present a reformulation and variation of the original algorithm which results in a greatly improved inverse transform, and consequent improved convolution algorithm for such functions. All require at most $O(N\log^2 N)$ operations where $N$ is the number of sample points. We also address implementation considerations and give heuristics for allowing reliable and computationally efficient floating point implementations of slightly modified algorithms. These claims are supported by extensive numerical experiments from our implementation in C …

Web Spoofing Revisited: Ssl And Beyond, Eileen Zishuang Ye, Yougu Yuan, Sean Smith

Computer Science Technical Reports

Can users believe what their browsers tell them? Even sophisticated Web users decide whether or not to trust a server based on browser cues such as location bar information, SSL icons, SSL warnings, certificate information, and response time. In their seminal work on Web spoofing, Felten et al showed how, in 1996, a malicious server could forge some of these cues. However, this work used genuine SSL sessions, and Web technology has evolved much since 1996. The Web has since become the pre-eminent medium for electronic service delivery to remote users, and the security of many commerce, government, and academic …

Future Directions For Mobile-Agent Research, David Kotz, Robert Gray, Daniela Rus

Computer Science Technical Reports

During a discussion in September 2000 the authors examined the future of research on mobile agents and mobile code. (A mobile agent is a running program that can move from host to host in network at times and to places of its own choosing.) In this paper we summarize and reflect on that discussion. It became clear that the field should shift its emphasis toward mobile code, in all its forms, rather than to continue its narrow focus on mobile agents. Furthermore, we encourage the development of modular components, so that application designers may take advantage of code mobility without …

Information-Theoretic Bounds On The Training And Testing Error Of Boosting, Sebastien M. Lahaie

Dartmouth College Undergraduate Theses

Boosting is a means of using weak learners as subroutines to produce a strong learner with markedly better accuracy. Recent results showing the connection between logistic regression and boosting provide the foundation for an information-theoretic analysis of boosting. We describe the analogy between boosting and gambling, which allows us to derive a new upper bound on training error. This upper bound explicitly describes the effect of noisy data on training error. We also use information-theoretic techniques to derive an alternative upper-bound on testing error which is independent of the size of the weak-learner space.