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Mustaque
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ItemA Crow or a Blackbird?: Using True Social Network and Tweeting Behavior to Detect Malicious Entities in Twitter(Georgia Institute of Technology, 2010) Balasubramaniyan, Vijay A. ; Maheswaran, Arjun ; Mahalingam, Viswanathan ; Ahamad, Mustaque ; Venkateswaran, H.The growing popularity of Twitter and its ability to enable near instantaneous sharing of information has made it a target of attacks by malicious entities who use it to spam and provide links to malware. There is evidence that these entities are using increasingly sophisticated techniques that mimic the behavior of reputed sources to avoid detection. We use novel mechanisms that utilize the true social network of users, the quality of information produced by them and their tweeting behavior to identify such entities. A scheme based on these mechanisms is even able to detect malicious entities that collude to establish dense social networks. Using actual data from a representative sample of 278, 758 Twitter users, we demonstrate the effectiveness of this approach by showing that (1) we identified 5334 accounts that had links to unsafe websites, and (2) over a period of 31 days, 181 accounts that our algorithm identified as potentially malicious were subsequently suspended by Twitter. We believe our algorithm is one of the first to automatically deal with a broad range of malicious entities present in Twitter.
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ItemCollective Endorsement and the Dissemination Problem in Malicious Environments(Georgia Institute of Technology, 2004-03-08) Lakshmanan, Subramanian ; Manohar, Deepak J. ; Ahamad, Mustaque ; Venkateswaran, H.We consider the problem of disseminating an update known to a set of servers to other servers in the system via a gossip protocol. Some of the servers can exhibit malicious behavior. We require that only the updates introduced by authorized clients are accepted by non-malicious servers. Spurious updates, in particular those generated by compromised nodes, are not accepted by non-malicious servers. We take the approach of collective endorsement where each server endorses an accepted update by computing a list of message authentication codes with symmetric keys allocated to it. We use a novel key allocation scheme that allocates a set of symmetric keys to each participating server to minimize the total number of keys. Our protocol is designed to minimize update diffusion time. In the absence of faulty nodes, its diffusion time is O(log n), which is the best possible time achieved when nodes only suffer from benign faults. If the actual number of Byzantine faults experienced during an update's dissemination is f, the diffusion time increases to O(log n + f). This is better than the latency of previously known protocols that take O(log n + b) time, where b is the assumed threshold that defines the maximum number of malicious servers that can be tolerated rather than f, the actual number of failures. The buffer requirements and message sizes are higher in our protocol than other known protocols and thus it trades off memory and bandwidth resources to improve latency.
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ItemResponsive Security for Stored Data(Georgia Institute of Technology, 2002) Lakshmanan, Subramanian ; Ahamad, Mustaque ; Venkateswaran, H.We present the design of a distributed store that offers various levels of security guarantees while tolerating a limited number of nodes that are compromised by an adversary. The store uses secret sharing schemes to offer security guarantees namely availability, confidentiality and integrity. However, a pure secret sharing scheme could suffer from performance problems and high access costs. We integrate secret sharing with replication for better performance and to keep access costs low. The tradeoffs involved between availability and access cost on one hand and confidentiality and integrity on the other are analyzed. Our system differs from traditional approaches such as state machine or quorum based replication that have been developed to tolerate Byzantine failures. Unlike such systems, we augment replication with secret sharing and demonstrate that such a hybrid scheme offers additional flexibility that is not possible with current schemes.
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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.