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Articles 391 - 420 of 772
Full-Text Articles in Computer Sciences
Web Spoofing 2001, Yougu Yuan, Eileen Zishuang Ye, Sean Smith Dartmouth College
Web Spoofing 2001, Yougu Yuan, Eileen Zishuang Ye, Sean Smith Dartmouth College
Computer Science Technical Reports
The Web is currently the pre-eminent medium for electronic service delivery to remote users. As a consequence, authentication of servers is more important than ever. Even sophisticated users base their decision whether or not to trust a site on browser cues---such as location bar information, SSL icons, SSL warnings, certificate information, response time, etc. In their seminal work on web spoofing, Felten et al showed how a malicious server could forge some of these cues---but using approaches that are no longer reproducible. However, subsequent evolution of Web tools has not only patched security holes---it has also added new technology to …
Securing Web Servers Against Insider Attack, Shan Jiang, Sean Smith, Kazuhiro Minami Dartmouth College
Securing Web Servers Against Insider Attack, Shan Jiang, Sean Smith, Kazuhiro Minami Dartmouth College
Computer Science Technical Reports
Too often, ``security of Web transactions'' reduces to ``encryption of the channel''---and neglects to address what happens at the server on the other end. This oversight forces clients to trust the good intentions and competence of the server operator---but gives clients no basis for that trust. Furthermore, despite academic and industrial research in secure coprocessing, many in the computer science community still regard ``secure hardware'' as a synonym for ``cryptographic accelerator.' This oversight neglects the real potential of COTS secure coprocessing technology to establish trusted islands of computation in hostile environments---such as at web servers with risk of insider attack. …
Supporting Adaptive Ubiquitous Applications With The Solar System, Guanling Chen, David Kotz
Supporting Adaptive Ubiquitous Applications With The Solar System, Guanling Chen, David Kotz
Computer Science Technical Reports
As we embed more computers into our daily environment, ubiquitous computing promises to make them less noticeable and help to prevent information overload. We see, however, few ubiquitous applications that are able to adapt to the dynamics of user, physical, and computational context. We believe that there are two challenges causing this lack of ubiquitous applications: there is no flexible and scalable way to support information collection and dissemination in a ubiquitous and mobile environment, and there is no general approach to building adaptive applications given heterogeneous contextual information. We propose a system infrastructure, Solar, to meet these challenges. Solar …
Outbound Authentication For Programmable Secure Coprocessors, S W. Smith
Outbound Authentication For Programmable Secure Coprocessors, S W. Smith
Computer Science Technical Reports
A programmable secure coprocessor platform can help solve many security problems in distributed computing. These solutions usually require that coprocessor applications be able to participate as full-fledged parties in distributed cryptographic protocols. Thus, to fully enable these solutions, a generic platform must not only provide programmability, maintenance, and configuration in the hostile field---it must also provide outbound authentication for the entities that result. A particular application on a particular untampered device must be able to prove who it is to a party on the other side of the Internet. To be effective, a secure outbound authentication service must closely mesh …
Mobile-Agent Versus Client/Server Performance: Scalability In An Information-Retrieval Task, Robert S. Gray, David Kotz, Ronald A. Peterson Jr, Peter Gerken, Martin Hofmann, Daria Chacon, Greg Hill, Niranjan Suri
Mobile-Agent Versus Client/Server Performance: Scalability In An Information-Retrieval Task, Robert S. Gray, David Kotz, Ronald A. Peterson Jr, Peter Gerken, Martin Hofmann, Daria Chacon, Greg Hill, Niranjan Suri
Computer Science Technical Reports
Mobile agents are programs that can jump from host to host in the network, at times and to places of their own choosing. Many groups have developed mobile-agent software platforms, and several mobile-agent applications. Experiments show that mobile agents can, among other things, lead to faster applications, reduced bandwidth demands, or less dependence on a reliable network connection. There are few if any studies of the scalability of mobile-agent servers, particularly as the number of clients grows. We present some recent performance and scalability experiments that compare three mobile-agent platforms with each other and with a traditional client/server approach. The …
Lock-Free Scheduling Of Logical Processes In Parallel Simulation, Xiaowen Liu, David M. Nicol, King Tan Dartmouth College
Lock-Free Scheduling Of Logical Processes In Parallel Simulation, Xiaowen Liu, David M. Nicol, King Tan Dartmouth College
Computer Science Technical Reports
With fixed lookahead information in a simulation model, the overhead of asynchronous conservative parallel simulation lies in the mechanism used for propagating time updates in order for logical processes to safely advance their local simulation clocks. Studies have shown that a good scheduling algorithm should preferentially schedule processes containing events on the critical path. This paper introduces a lock-free algorithm for scheduling logical processes in conservative parallel discrete-event simulation on shared-memory multiprocessor machines. The algorithm uses fetch\&add operations that help avoid inefficiencies associated with using locks. The lock-free algorithm is robust. Experiments show that, compared with the scheduling algorithm using …
Ambiguity-Directed Sampling For Qualitative Analysis Of Sparse Data From Spatially-Distributed Physical Systems, Chris Bailey-Kellogg, Naren Ramakrishnan
Ambiguity-Directed Sampling For Qualitative Analysis Of Sparse Data From Spatially-Distributed Physical Systems, Chris Bailey-Kellogg, Naren Ramakrishnan
Computer Science Technical Reports
A number of important scientific and engineering applications, such as fluid dynamics simulation and aircraft design, require analysis of spatially-distributed data from expensive experiments and complex simulations. In such data-scarce applications, it is advantageous to use models of given sparse data to identify promising regions for additional data collection. This paper presents a principled mechanism for applying domain-specific knowledge to design focused sampling strategies. In particular, our approach uses ambiguities identified in a multi-level qualitative analysis of sparse data to guide iterative data collection. Two case studies demonstrate that this approach leads to highly effective sampling decisions that are also …
Reconstructing Ancient Egyptian Tombs, Hany Farid
Reconstructing Ancient Egyptian Tombs, Hany Farid
Computer Science Technical Reports
From the pyramids of Giza to the tombs of Thebes (modern Luxor), ancient Egypt's glorious history has produced remarkable architecture. Sadly, the nearly four million yearly tourists have taken a heavy toll on many of these ancient structures. Of particular concern are many of the tombs located opposite to Luxor on the western bank of the Nile. Digital reconstruction of these tombs has the potential to help document and preserve these important historical structures. Photographing and reconstruction of these tombs poses new and unique problems that this paper begins to address. Techniques for removing image distortions, recovering 3-D shape, and …
Bayes Optimal Metasearch: A Probabilistic Model For Combining The Results Of Multiple Retrieval Systems, Javed A. Aslam, Mark Montague
Bayes Optimal Metasearch: A Probabilistic Model For Combining The Results Of Multiple Retrieval Systems, Javed A. Aslam, Mark Montague
Computer Science Technical Reports
We introduce a new, probabilistic model for combining the outputs of an arbitrary number of query retrieval systems. By gathering simple statistics on the average performance of a given set of query retrieval systems, we construct a Bayes optimal mechanism for combining the outputs of these systems. Our construction yields a metasearch strategy whose empirical performance nearly always exceeds the performance of any of the constituent systems. Our construction is also robust in the sense that if ``good'' and ``bad'' systems are combined, the performance of the composite is still on par with, or exceeds, that of the best constituent …
A Survey Of Context-Aware Mobile Computing Research, Guanling Chen, David Kotz
A Survey Of Context-Aware Mobile Computing Research, Guanling Chen, David Kotz
Computer Science Technical Reports
Context-aware computing is a mobile computing paradigm in which applications can discover and take advantage of contextual information (such as user location, time of day, nearby people and devices, and user activity). Since it was proposed about a decade ago, many researchers have studied this topic and built several context-aware applications to demonstrate the usefulness of this new technology. Context-aware applications (or the system infrastructure to support them), however, have never been widely available to everyday users. In this survey of research on context-aware systems and applications, we looked in depth at the types of context used and models of …
Performance Analysis Of Mobile Agents For Filtering Data Streams On Wireless Networks, David Kotz, George Cybenko, Robert S. Gray, Guofei Jiang, Ronald A. Peterson, Martin O. Hofmann, Daria A. Chacon, Kenneth R. Whitebread
Performance Analysis Of Mobile Agents For Filtering Data Streams On Wireless Networks, David Kotz, George Cybenko, Robert S. Gray, Guofei Jiang, Ronald A. Peterson, Martin O. Hofmann, Daria A. Chacon, Kenneth R. Whitebread
Computer Science Technical Reports
Wireless networks are an ideal environment for mobile agents, since their mobility allows them to move across an unreliable link to reside on a wired host, next to or closer to the resources that they need to use. Furthermore, client-specific data transformations can be moved across the wireless link and run on a wired gateway server, reducing bandwidth demands. In this paper we examine the tradeoffs faced when deciding whether to use mobile agents in a data-filtering application where numerous wireless clients filter information from a large data stream arriving across the wired network. We develop an analytical model and …
The Complexity Of Planning With Partially-Observable Markov Decision Processes, Martin Mundhenk
The Complexity Of Planning With Partially-Observable Markov Decision Processes, Martin Mundhenk
Computer Science Technical Reports
This work surveys results on the complexity of planning under uncertainty. The planning model considered is the partially-observable Markov decision process. The general planning problems are, given such a process, (a) to calculate its performance under a given control policy, (b) to find an optimal or approximate optimal control policy, and (c) to decide whether a good policy exists. The complexity of this and related problems depend on a variety of factors, including the observability of the process state, the compactness of the process representation, the type of policy, or even the number of actions relative to the number of …
Approximation Algorithms For The Minimum Bends Traveling Salesman Problem, Cliff Stein, David P. Wagner
Approximation Algorithms For The Minimum Bends Traveling Salesman Problem, Cliff Stein, David P. Wagner
Computer Science Technical Reports
The problem of traversing a set of points in the order that minimizes the total distance traveled (traveling salesman problem) is one of the most famous and well-studied problems in combinatorial optimization. It has many applications, and has been a testbed for many of the must useful ideas in algorithm design and analysis. The usual metric, minimizing the total distance traveled, is an important one, but many other metrics are of interest. In this paper, we introduce the metric of minimizing the number of turns in the tour, given that the input points are in the Euclidean plane. To our …
Performance Analysis Of Mobile Agents For Filtering Data Streams On Wireless Networks, David Kotz, Guofei Jiang, Robert Gray, George Cybenko, Ronald A. Peterson
Performance Analysis Of Mobile Agents For Filtering Data Streams On Wireless Networks, David Kotz, Guofei Jiang, Robert Gray, George Cybenko, Ronald A. Peterson
Computer Science Technical Reports
Wireless networks are an ideal environment for mobile agents, because their mobility allows them to move across an unreliable link to reside on a wired host, next to or closer to the resources they need to use. Furthermore, client-specific data transformations can be moved across the wireless link, and run on a wired gateway server, with the goal of reducing bandwidth demands. In this paper we examine the tradeoffs faced when deciding whether to use mobile agents to support a data-filtering application, in which numerous wireless clients filter information from a large data stream arriving across the wired network. We …
A Formal Semantics For Spki, Jon Howell, David Kotz
A Formal Semantics For Spki, Jon Howell, David Kotz
Computer Science Technical Reports
We extend the logic and semantics of authorization due to Abadi, Lampson, et al. to support restricted delegation. Our formal model provides a simple interpretation for the variety of constructs in the Simple Public Key Infrastructure (SPKI), and lends intuition about possible extensions. We discuss both extensions that our semantics supports and extensions that it cautions against.
Landmarks For Absolute Localization, Jon Howell, Keith Kotay
Landmarks For Absolute Localization, Jon Howell, Keith Kotay
Computer Science Technical Reports
For certain experiments in mobile robotics, it is convenient to eliminate positional estimation error in the interest of analyzing other parts of the experiment. We designed and implemented a simple, accurate scheme for encoding and recovering absolute position information. The encoding is a two-dimensional image printed on the plane of the floor, and the absolute position information is recovered using a downward-looking video camera mounted on a mobile robot.
An Access-Control Calculus For Spanning Administrative Domains, Jon Howell, David Kotz
An Access-Control Calculus For Spanning Administrative Domains, Jon Howell, David Kotz
Computer Science Technical Reports
In our quest to give users uniform access to resources unimpeded by administrative boundaries, we discovered that we needed transitive sharing among users, with the possibility of restricted access along each sharing link. To achieve that goal, we extend Lampson et al.'s calculus for access control to support restricted delegations. We discuss the advantages of our extension, including the simplification of constructs like ACLs and statement expiration. We also apply our extension to model the Simple Public Key Infrastructure and make suggestions about its future development. Our extended calculus exposes some surprising consequences in such systems that use restricted delegation.
Sar By Ms For Functional Genomics (Structure-Activity Relation By Mass Spectrometry), Bruce Randall Donald, Chris Bailey-Kellogg, John J. Kelley Iii, Cliff Stein
Sar By Ms For Functional Genomics (Structure-Activity Relation By Mass Spectrometry), Bruce Randall Donald, Chris Bailey-Kellogg, John J. Kelley Iii, Cliff Stein
Computer Science Technical Reports
Large-scale functional genomics will require fast, high-throughput experimental techniques, coupled with sophisticated computer algorithms for data analysis and experiment planning. In this paper, we introduce a combined experimental-computational protocol called Structure-Activity Relation by Mass Spectrometry (SAR by MS), which can be used to elucidate the function of protein-DNA or protein-protein complexes. We present algorithms for SAR by MS and analyze their complexity. Carefully-designed Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight (MALDI TOF) and Electrospray Ionization (ESI) assays require only femtomolar samples, take only microseconds per spectrum to record, enjoy a resolution of up to one dalton in $10^6$, and (in the case of …
A Game-Theoretic Formulation Of Multi-Agent Resource Allocation, Jonathan Bredin, Rajiv T. Maheswaran, Cagri Imer, Tamer Basar, David Kotz, Daniela Rus
A Game-Theoretic Formulation Of Multi-Agent Resource Allocation, Jonathan Bredin, Rajiv T. Maheswaran, Cagri Imer, Tamer Basar, David Kotz, Daniela Rus
Computer Science Technical Reports
This paper considers resource allocation in a network with mobile agents competing for computational priority. We formulate this problem as a multi-agent game with the players being agents purchasing service from a common server. We show that there exists a computable Nash equilibrium when agents have perfect information into the future. We simulate a network of hosts and agents using our strategy to show that our resource-allocation mechanism effectively prioritizes agents according to their endowments.
An Environment For The Facilitation Of Robotic Programming, Artem Lifschitz
An Environment For The Facilitation Of Robotic Programming, Artem Lifschitz
Computer Science Technical Reports
I have developed, tested, and evaluated a robot programming environment organized as a library of flexible data structures to facilitate the creation of robotics programs. Abstractions are the basis of all of the achievements of Computer Science, and if it were possible to create a truly flexible, generic abstraction for the programming of robots -- the science of robotics could advance at a faster pace. For this reason, I have attempted to implement the abstraction of low-level commands, and the assembling of them into hierarchies of higher-level actions. My libraries provide mechanisms for the manipulation and queuing of actions, as …
Mobile-Agent Planning In A Market-Oriented Environment, Jonathan Bredin, David Kotz, Daniela Rus
Mobile-Agent Planning In A Market-Oriented Environment, Jonathan Bredin, David Kotz, Daniela Rus
Computer Science Technical Reports
We propose a method for increasing incentives for sites to host arbitrary mobile agents in which mobile agents purchase their computing needs from host sites. We present a scalable market-based CPU allocation policy and an on-line algorithm that plans a mobile agent's expenditure over a multihop ordered itinerary. The algorithm chooses a set of sites at which to execute and computational priorities at each site to minimize execution time while preserving a prespecified budget constraint. We present simulation results of our algorithm to show that our allocation policy and planning algorithm scale well as more agents are added to the …
Using Haptic Vector Fields For Animation Motion Control, Bruce Randall Donald, Frederick Henle
Using Haptic Vector Fields For Animation Motion Control, Bruce Randall Donald, Frederick Henle
Computer Science Technical Reports
We are exploring techniques for animation authoring and editing using a haptic force-feedback device. In our system, a family of animations is encoded by a bundle of trajectories. This bundle in turn defines a time-varying, higher-order vector field on a configuration space for the animation. A haptic input device provides a low-dimensional parameterization of the resulting dynamical system, and the haptic force feedback permits browsing and editing of the space of animations, by allowing the user to experience the vector field as physical forces.
Greedy Approximation Algorithms For K-Medians By Randomized Rounding, Neal E. Young
Greedy Approximation Algorithms For K-Medians By Randomized Rounding, Neal E. Young
Computer Science Technical Reports
We give an improved approximation algorithm for the general k-medians problem. Given any \epsilon>0, the algorithm finds a solution of total distance at most D(1+\epsilon) using at most k ln(n+n/\epsilon) medians (a.k.a. sites), provided some solution of total distance D using k medians exists. This improves over the best previous bound (w.r.t. the number of medians) by a factor of \Omega(1/\epsilon) provided 1/\epsilon=n^O(1). The algorithm is a greedy algorithm, derived using the method of oblivious randomized rounding. It requires at most k ln(n+n/\epsilon) linear-time iterations. We also derive algorithms for fractional and weighted variants of the problem.
Hey, You Got Your Language In My Operating System!, Jon Howell, Mark Montague
Hey, You Got Your Language In My Operating System!, Jon Howell, Mark Montague
Computer Science Technical Reports
Several projects in the operating systems research community suggest a trend of convergence among features once divided between operating systems and languages. We describe how partial evaluation and transformational programming systems apply to this trend by providing a general framework for application support, from compilation to run-time services. We contend that the community will no longer think of implementing a static collection of services and calling it an operating system; instead, this general framework will allow applications to be flexibly configured, and the ``operating system'' will simply be the application support that is supplied at run-time.
Snowflake: Spanning Administrative Domains, Jon Howell, David Kotz
Snowflake: Spanning Administrative Domains, Jon Howell, David Kotz
Computer Science Technical Reports
Many distributed systems provide a ``single-system image'' to their users, so the user has the illusion that they are using a single system when in fact they are using many distributed resources. It is a powerful abstraction that helps users to manage the complexity of using distributed resources. The goal of the Snowflake project is to discover how single-system images can be made to span administrative domains. Our current prototype organizes resources in namespaces and distributes them using Java Remote Method Invocation. Challenging issues include how much flexibility should be built into the namespace interface, and how transparent the network …
Utility Driven Mobile-Agent Scheduling, Jonathan Bredin, David Kotz, Daniela Rus
Utility Driven Mobile-Agent Scheduling, Jonathan Bredin, David Kotz, Daniela Rus
Computer Science Technical Reports
Mobile agents are programs capable of migrating from one host machine to another. We propose that mobile agents purchase resource access rights from host machines thereby establishing a market for computational resources and giving agents a metric to evenly distribute themselves throughout the network. Market participation requires quantitative information about resource consumption to define demand and calculate utility. We create a formal utility model to derive user-demand functions, allowing agents to efficiently plan expenditure and deal with price fluctuations. By quantifying demand and utility, resource owners can precisely set a value for a good. We simulate our model in a …
Abstractions For Simplifying Planning In Self-Reconfigurable Robotic Systems, Craig Mcgray, Daniela Rus
Abstractions For Simplifying Planning In Self-Reconfigurable Robotic Systems, Craig Mcgray, Daniela Rus
Computer Science Technical Reports
In [KVRM], we described a three-dimensional self-reconfiguring robot module called the Molecule Robot. In this paper, we provide a system of abstractions for modules in self-reconfigurable robotic systems, and show how this system can be used to simplify the motion planning of the Molecule Robot system.
Applications Of Parallel I/O, Ron Oldfield, David Kotz
Applications Of Parallel I/O, Ron Oldfield, David Kotz
Computer Science Technical Reports
Scientific applications are increasingly being implemented on massively parallel supercomputers. Many of these applications have intense I/O demands, as well as massive computational requirements. This paper is essentially an annotated bibliography of papers and other sources of information about scientific applications using parallel I/O. It will be updated periodically.
Straightforward Java Persistence Through Checkpointing, Jon Howell
Straightforward Java Persistence Through Checkpointing, Jon Howell
Computer Science Technical Reports
Several techniques have been proposed for adding persistence to the Java language environment. This paper describes a scheme based on checkpointing the Java Virtual Machine, and compares the scheme to other techniques. Checkpointing offers two unique advantages: first, the implementation is independent of the JVM implementation, and therefore survives JVM updates; second, because checkpointing saves and restores execution state, even threads become persistent entities.
An Implementation Of The Vesta Parallel File System Api On The Galley Parallel File System, Matthew P. Carter, David Kotz
An Implementation Of The Vesta Parallel File System Api On The Galley Parallel File System, Matthew P. Carter, David Kotz
Computer Science Technical Reports
To demonstrate the flexibility of the Galley parallel file system and to analyze the efficiency and flexibility of the Vesta parallel file system interface, we implemented Vesta's application-programming interface on top of Galley. We implemented the Vesta interface using Galley's file-access methods, whose design arose from extensive testing and characterization of the I/O requirements of scientific applications for high-performance multiprocessors. We used a parallel CPU, parallel I/O, out-of-core matrix-multiplication application to test the Vesta interface in both its ability to specify data access patterns and in its run-time efficiency. In spite of its powerful ability to specify the distribution of …