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ItemITR/SI: Guarding the next internet frontier: countering denial of information(Georgia Institute of Technology, 2008-12-19) Ahamad, Mustaque ; Omiecinski, Edward ; Pu, Calton ; Mark, Leo ; Liu, Ling ; Georgia Institute of Technology. Office of Sponsored Programs ; Georgia Institute of Technology. College of Computing ; Georgia Institute of Technology. Office of Sponsored Programs
ItemSystem Support for Robust, Collaborative Applications(Georgia Institute of Technology, 1995) Chelliah, Muthusamy ; Ahamad, MustaqueTraditional transaction models ensure robustness for distributed applications through the properties of view and failure atomicity. It has generally been felt that such atomicity properties are restrictive for a wide range of application domains; this is particularly true for robust, collaborative applications because such applications have concurrent components that are inherently long-lived and that cooperate. Recent advances in extended transaction models can be exploited to structure long-lived and cooperative computations. Applications can use a combination of such models to achieve the desired degree of robustness; hence, we develop a system which can support a number of flexible transaction models, with correctness semantics that extend or relax serializability. We analyze two concrete CSCW applications - collaborative editor and meeting scheduler. We show how a combination of two extended transaction models, that promote split and cooperating actions, facilitates robust implementations of these collaborative applications. Thus, we conclude that a system that implements multiple transaction models provides flexible support for building robust, collaborative applications.
ItemA Secure and Highly Available Distributed Store for Meeting Diverse Data Storage Needs(Georgia Institute of Technology, 2000) Lakshmanan, Subramanian ; Ahamad, Mustaque ; Venkateswaran, H.As computers become pervasive in environments like the home and community, data repositories that can maintain the long term state of applications will become increasingly important. Because of the greater reliance of people on such applications and the potentially sensitive nature of the data manipulated by them, the repository must be highly available and it should provide secure access to data. Furthermore, many different types of data, ranging from private data belonging to a single user to data shared across different users may be stored in the repository. We present the design of a distributed data repository, called a secure store, which can meet the data access needs of diverse applications. We develop protocols that replicate data at multiple servers to enhance availability and work even when a limited number of compromised servers exhibit arbitrary failure behavior. We also discuss how the nature of the data that is stored in the secure store impacts the availability and costs associated with data access.
ItemUsing Byzantine Quorum Systems to Manage Confidential Data(Georgia Institute of Technology, 2004-04-01) Subbiah, Arun ; Ahamad, Mustaque ; Blough, Douglas M.This paper addresses the problem of using proactive cryptosystems for generic data storage and retrieval. Proactive cryptosystems provide high security and confidentiality guarantees for stored data, and are capable of withstanding attacks that may compromise all the servers in the system over time. However, proactive cryptosystems are unsuitable for generic data storage uses for two reasons. First, proactive cryptosystems are usually used to store keys, which are rarely updated. On the other hand, generic data could be actively written and read. The system must therefore be highly available for both write and read operations. Second, existing share renewal protocols (the critical element to achieve proactive security) are expensive in terms of computation and communication overheads, and are time consuming operations. Since generic data will be voluminous, the share renewal process will consume substantial system resources and cause a significant amount of system downtime. Two schemes are proposed that combine Byzantine quorum systems and proactive secret sharing techniques to provide high availability and security guarantees for stored data, while reducing the overhead incurred during the share renewal process. Several performance metrics that can be used to evaluate proactively-secure generic data storage schemes are identified. The proposed schemes are thus shown to render proactive systems suitable for confidential generic data storage.
ItemA Characterization of Scalable Shared Memories(Georgia Institute of Technology, 1993) Kohli, Prince ; Neiger, Gil ; Ahamad, MustaqueThe traditional consistency requirements of shared memory are expensive to provide both in large scale multiprocessor systems and also in distributed systems that implement a shared memory abstraction in software. As a result, several memory systems have been proposed that enhance performance and scalability of shared memories by providing weaker consistency guarantees. Often, different models are used to describe such memories which makes it difficult to relate and compare them. We develop a simple non-operational model and identify parameters that can be varied to describe not only the existing memories but also to identify new ones. We show how such a uniform framework makes it easy to compare and relate the various memories. We also use the model to show that a well known software solution to the critical section problem can be used to distinguish the RC[subscript sc] and RC[subscript pc] memories explored in the DASH architecture.
ItemResponsiveness and Consistency Tradeoffs in Interactive Groupware(Georgia Institute of Technology, 1998) Bhola, Sumeer Kumar ; Banavar, Guruduth S. ; Ahamad, MustaqueInteractive (or Synchronous) groupware is increasingly being deployed in widely distributed environments. Users of such applications are accustomed to direct manipulation interfaces that require fast response time. The state that enables interaction among distributed users can be replicated to provide acceptable response time in the presence of high communication latencies. We describe and evaluate design choices for protocols that maintain consistency of such state. In particular, we develop workloads which model user actions, identify the metrics important from a user's viewpoint, and do detailed simulations of a number of protocols to evaluate how effective they are in meeting user requirements.
ItemEnabling Interactive Applications over the Internet(Georgia Institute of Technology, 1999) Krishnaswamy, Vijaykumar ; Ganev, Ivan Borissov ; Dharap, Jaideep M. ; Ahamad, MustaqueAs computers become pervasive in the home and community and homes become better connected, new applications will be deployed over the Internet. Interactive Distributed Applications involve users in multiple locations, across a wide area network, who interact and cooperate by manipulating shared objects. A timely response to user actions, which can potentially update the state of the objects, is an important requirement. Because of the inherent heterogeneity of the environment, traditionally distributed applications are built using technologies like distributed objects. These technologies are built around a central server paradigm which is undesirable because the response time for the actions of interactive users is always subject to communication latencies.Our approach is to extend these technologies with aggressive caching and replication mechanisms without changing the remote object interface to the applications. Thus, caching and replication are done transparently to provide interactive response time and to improve scalability. A flexible caching framework is presented, where objects can be cached in an application specific manner. It provides multiple consistency protocols that enable tradeoffs between the consistency of a cached object's state at a particular client, and the communication resources available at the client. At runtime, clients can specify their consistency requirements which can vary across different clients. This can be done via a Quality of Service specification interface that is meaningful at the application level. This paper presents the caching framework, its implementation and some preliminary performance results.
ItemRobust State Sharing for Wide Area Distributed Applications(Georgia Institute of Technology, 1997) Topol, Brad Byer ; Ahamad, Mustaque ; Stasko, John T.In this article, we present the Mocha wide area computing infrastructure we are currently developing. Mocha provides support for robust shared objects on heterogeneous platforms, and utilizes advanced distributed shared memory techniques for maintaining consistency of shared objects that are replicated at multiple nodes to improve performance. In addition, our system handles failures that we feel will be common in wide area environments. For example, to ensure that the state of an object is not lost due to a node failure, updated state of the object can be disseminated to several other nodes. The overhead of such state dissemination can be controlled based on the level of availability needed for shared objects. We have used an approach that makes use of multiple communication protocols to improve the efficiency of shared object state transfers in Mocha. We also provide an empirical evaluation of our prototype implementation for both local and wide area networks and present a sample home service application written with the system.
ItemUsing multicast communication for resource finding in distributed systems(Georgia Institute of Technology, 1991) Ahamad, Mustaque ; Georgia Institute of Technology. Office of Sponsored Programs ; Georgia Institute of Technology. College of Computing ; Georgia Institute of Technology. Office of Sponsored Programs
ItemSecuring Context-Aware Applications Using Environment Roles(Georgia Institute of Technology, 2000) Covington, Michael J. ; Long, Wende ; Srinivasan, Srividhya ; Dey, Anind K. ; Ahamad, Mustaque ; Abowd, Gregory D.In the future, a largely invisible and ubiquitous computing infrastructure will assist people with a variety of activities in the home and at work. The applications that will be deployed in such systems will create and manipulate private information and will provide access to a variety of other resources. Securing such applications is challenging for a number of reasons. Unlike traditional systems where access control has been explored, access decisions may depend on the context in which requests are made. We show how the well-developed notion of roles can be used to capture security-relevant context of the environment in which access requests are made. By introducing environment roles, we create a uniform access control framework that can be used to secure context-aware applications. We also present a security architecture that supports security policies that make use of environment roles to control access to resources.