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Full-Text Articles in Physical Sciences and Mathematics
Statistical Tools For Digital Image Forensics, Alin C. Popescu
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 …
Performance Evaluation Of A Resource Discovery Service, Jue Wang
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 …
Heterogeneous Self-Reconfiguring Robotics, Robert Charles Fitch
Heterogeneous Self-Reconfiguring Robotics, Robert Charles Fitch
Dartmouth College Ph.D Dissertations
Self-reconfiguring (SR) robots are modular systems that can autonomously change shape, or reconfigure, for increased versatility and adaptability in unknown environments. In this thesis, we investigate planning and control for systems of non-identical modules, known as heterogeneous SR robots. Although previous approaches rely on module homogeneity as a critical property, we show that the planning complexity of fundamental algorithmic problems in the heterogeneous case is equivalent to that of systems with identical modules. Primarily, we study the problem of how to plan shape changes while considering the placement of specific modules within the structure. We characterize this key challenge in …
Solar: Building A Context Fusion Network For Pervasive Computing, Guanling Chen
Solar: Building A Context Fusion Network For Pervasive Computing, Guanling Chen
Dartmouth College Ph.D Dissertations
The complexity of developing context-aware pervasive-computing applications calls for distributed software infrastructures that assist applications to collect, aggregate, and disseminate contextual data. In this dissertation, we present a Context Fusion Network (CFN), called Solar, which is built with a scalable and self-organized service overlay. Solar is flexible and allows applications to select distributed data sources and compose them with customized data-fusion operators into a directed acyclic information flow graph. Such a graph represents how an application computes high-level understandings of its execution context from low-level sensory data. To manage application-specified operators on a set of overlay nodes called Planets, Solar …
Type-Safe Operating System Abstractions, Lea Wittie
Type-Safe Operating System Abstractions, Lea Wittie
Dartmouth College Ph.D Dissertations
Operating systems and low-level applications are usually written in languages like C and assembly, which provide access to low-level abstractions. These languages have unsafe type systems that allow many bugs to slip by programmers. For example, in 1988, the Internet Worm exploited several insecure points in Unix including the finger command. A call to finger with an unexpected argument caused a buffer overflow, leading to the shutdown of most Internet traffic. A finger application written in a type-safe language would have prevented its exploit and limited the points the Internet Worm could attack. Such vulnerabilities are unacceptable in security-critical applications …
Simulating Mobile Ad Hoc Networks: A Quantitative Evaluation Of Common Manet Simulation Models, Calvin Newport
Simulating Mobile Ad Hoc Networks: A Quantitative Evaluation Of Common Manet Simulation Models, Calvin Newport
Dartmouth College Undergraduate Theses
Because it is difficult and costly to conduct real-world mobile ad hoc network experiments, researchers commonly rely on computer simulation to evaluate their routing protocols. However, simulation is far from perfect. A growing number of studies indicate that simulated results can be dramatically affected by several sensitive simulation parameters. It is also commonly noted that most simulation models make simplifying assumptions about radio behavior. This situation casts doubt on the reliability and applicability of many ad hoc network simulation results. In this study, we begin with a large outdoor routing experiment testing the performance of four popular ad hoc algorithms …
Ppl: A Packet Processing Language, Eric G. Krupski
Ppl: A Packet Processing Language, Eric G. Krupski
Dartmouth College Undergraduate Theses
Any computing device or system that uses the internet needs to analyze and identify the contents of network packets. Code that does this is often written in C, but reading, identifying, and manipulating network packets in C requires writing tricky and tedious code. Previous work has offered specification languages for describing the format of network packets, which would allow packet type identification without the hassles of doing this task in C. For example, McCann and Chandra's Packet Types [3] system allows the programmer to define arbitrary packet types and generates C unctions which match given data against a specified packet …
Mobile Agents Simulation With Dassf, Nikita E. Dubrovsky
Mobile Agents Simulation With Dassf, Nikita E. Dubrovsky
Dartmouth College Undergraduate Theses
Mobile agents are programs that can migrate from machine to machine in a network of computers and have complete control over their movement. Since the performance space of mobile agents has not been characterized fully, assessing the effectiveness of using mobile agents over a traditional client/server approach currently requires implementing an agent system and running time-consuming experiments. This report presents a simple mobile-agent simulation that can provide quick information on the performance and scalability of a generic information retrieval (IR) mobile-agent system under different network configurations. The simulation is built using the DaSSF and DaSSFNet frameworks, resulting in high performance …
Spatial Multipath Location Aided Routing, Soumendra Nanda
Spatial Multipath Location Aided Routing, Soumendra Nanda
Dartmouth College Master’s Theses
Mobile ad-hoc networks (MANETs) are infrastructure-free networks of mobile nodes that communicate with each other wirelessly. There are several routing schemes that have been proposed and several of these have been already extensively simulated or implemented as well. The primary applications of such networks have been in disaster relief operations, military use, conferencing and environment sensing. There are several ad hoc routing algorithms at present that utilize position information (usually in two dimensional terms) to make routing decisions at each node. Our goal is to utilize three-dimensional (3D) position information to provide more reliable as well as efficient routing for …
Scheduling Pipelined, Multi-Threaded Programs In Linux, Brunn W. Roysden
Scheduling Pipelined, Multi-Threaded Programs In Linux, Brunn W. Roysden
Dartmouth College Undergraduate Theses
A process causes latency when it performs I/O or communication. Pipelined processes mitigate latency by concurrently executing multiple threads--- sequences of operations--- and overlapping computation, communication, and I/O. When more than one thread is ready to run, the scheduler determines which thread in fact runs. This paper presents techniques for scheduling pipelines, with the following three findings. First, using Linux kernel version 2.6 and the NPTL threads package, we observe a 3-6% performance improvement over kernel version 2.4 and the LinuxThreads package. Second, we test techniques that both take advantage of prior knowledge about whether a program is I/O-bound or …
Efficient Wait-Free Implementation Of Atomic Multi-Word Buffer, Rachel B. Ringel
Efficient Wait-Free Implementation Of Atomic Multi-Word Buffer, Rachel B. Ringel
Dartmouth College Undergraduate Theses
This thesis proposes algorithms for implementing a atomic multi-word buffer, which can be accessed concurrently by multiple readers and a single writer, from the hardware-supported shared memory. The algorithms are required to be wait-free: each process reads or writes the multi-word buffer in a bounded number of its own steps, regardless of whether other processes are fast, slow or have crashed. Our first algorithm is built from multi-writer, multi-reader variables whereas the second algorithm is built from single-writer, multi-reader variables. For either algorithm, the worst-case running time of a read or a write operation on the m-word buffer is O(m). …
Greenpass Client Tools For Delegated Authorization In Wireless Networks, Nicholas C. Goffee
Greenpass Client Tools For Delegated Authorization In Wireless Networks, Nicholas C. Goffee
Dartmouth College Master’s Theses
Dartmouth's Greenpass project seeks to provide strong access control to a wireless network while simultaneously providing flexible guest access; to do so, it augments the Wi-Fi Alliance's existing WPA standard, which offers sufficiently strong user authentication and access control, with authorization based on SPKI certificates. SPKI allows certain local users to delegate network access to guests by issuing certificates that state, in essence, "he should get access because I said it's okay." The Greenpass RADIUS server described in Kim's thesis [55] performs an authorization check based on such statements so that guests can obtain network access without requiring a busy …
Greenpass Radius Tools For Delegated Authorization In Wireless Networks, Sung Hoon Kim
Greenpass Radius Tools For Delegated Authorization In Wireless Networks, Sung Hoon Kim
Dartmouth College Master’s Theses
Dartmouth's Greenpass project extends how public key cryptography can be used to secure the wireless LAN with a RADIUS (Remote Authentication Dial In User Service) server that is responsible for handling authentication requests from clients (called supplicants in the 802.1x authentication model). This thesis describes the design and implementation of the authentication process of Greenpass, specifically what decisions are made in determining who is granted access and how a small modification of already existing protocols can be used to provide guest access in a way that better reflects how delegation of authority works in the real world. Greenpass takes advantage …
Testing The Greenpass Wireless Security System, Kimberly S. Powell
Testing The Greenpass Wireless Security System, Kimberly S. Powell
Dartmouth College Undergraduate Theses
Greenpass, developed by Nick Goffee, Sung Hoon Kim, Meiyuan Zhao and John Marchesini under the supervision of Sean Smith and Punch Taylor, is a wireless security solution that implements SPKI/SDSI delegation on top of X.509 keypairs within the EAP-TLS authentication protocol. This system aims to model the decentralized way that authorization flows in real-world enterprise settings and provide a seamless solution that allows for easy access to all resources in the network by both registered users and authorized guests. These goals are achieved through the deployment of a delegation tool, which allows an active entity associated to the organization's network …
A Secure Network Node Approach To The Policy Decision Point In Distributed Access Control, Geoffrey H. Stowe
A Secure Network Node Approach To The Policy Decision Point In Distributed Access Control, Geoffrey H. Stowe
Dartmouth College Undergraduate Theses
To date, the vast majority of access control research and development has been on gathering, managing, and exchanging information about users. But an equally important component which has yet to be fully developed is the Policy Decision Point - the system that decides whether an access request should be granted given certain attributes of the requestor. This paper describes the research and implementation of a new PDP system for an undergraduate honors project. This PDP system employs three unique features which differentiate it from existing technology: collaboration capabilities, trusted management, and interoperability with other access control systems. Security considerations and …
Synchronizing Keyframe Facial Animation To Multiple Text-To-Speech Engines And Natural Voice With Fast Response Time, William H. Pechter
Synchronizing Keyframe Facial Animation To Multiple Text-To-Speech Engines And Natural Voice With Fast Response Time, William H. Pechter
Dartmouth College Undergraduate Theses
This thesis aims to create an automated lip-synchronization system for real-time applications. Specifically, the system is required to be fast, consist of a limited number of keyframes with small memory requirements, and create fluid and believable animations that synchronize with text-to-speech engines as well as raw voice data. The algorithms utilize traditional keyframe animation and a novel method of keyframe selection. Additionally, phoneme-to-keyframe mapping, synchronization, and simple blending rules are employed. The algorithms provide blending between keyframe images, borrow information from neighboring phonemes, accentuate phonemes b, p and m, differentiate between keyframes for phonemes with allophonic variations, and provide prosodromic …
Enhancing Expressiveness Of Speech Through Animated Avatars For Instant Messaging And Mobile Phones, Joseph E. Pechter
Enhancing Expressiveness Of Speech Through Animated Avatars For Instant Messaging And Mobile Phones, Joseph E. Pechter
Dartmouth College Undergraduate Theses
This thesis aims to create a chat program that allows users to communicate via an animated avatar that provides believable lip-synchronization and expressive emotion. Currently many avatars do not attempt to do lip-synchronization. Those that do are not well synchronized and have little or no emotional expression. Most avatars with lip synch use realistic looking 3D models or stylized rendering of complex models. This work utilizes images rendered in a cartoon style and lip-synchronization rules based on traditional animation. The cartoon style, as opposed to a more realistic look, makes the mouth motion more believable and the characters more appealing. …
Parallel Out-Of-Core Sorting: The Third Way, Geeta Chaudhry
Parallel Out-Of-Core Sorting: The Third Way, Geeta Chaudhry
Dartmouth College Ph.D Dissertations
Sorting very large datasets is a key subroutine in almost any application that is built on top of a large database. Two ways to sort out-of-core data dominate the literature: merging-based algorithms and partitioning-based algorithms. Within these two paradigms, all the programs that sort out-of-core data on a cluster rely on assumptions about the input distribution. We propose a third way of out-of-core sorting: oblivious algorithms. In all, we have developed six programs that sort out-of-core data on a cluster. The first three programs, based completely on Leighton's columnsort algorithm, have a restriction on the maximum problem size that they …
Access Control In A Distributed Decentralized Network: An Xml Approach To Network Security Using Xacml And Saml, Paul J. Mazzuca
Access Control In A Distributed Decentralized Network: An Xml Approach To Network Security Using Xacml And Saml, Paul J. Mazzuca
Dartmouth College Undergraduate Theses
The development of eXtensible Distributed Access Control (XDAC) systems is influenced by the transference of data access and storage from the local computer to the network. In this distributed system, access control is determined by independent components which transmit requests and decisions over a network, utilizing XML signing capabilities found in the Security Assertion Markup Language (SAML). All resources in the XDAC system are protected by the first component, a Policy Enforcement Point (PEP), which acts as the main divider between the requesting entity and the requested resource. The PEP grants access to a resource only if the second component, …