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55
Towards secure and scalable computation in peertopeer networks
 In FOCS
, 2006
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Ulysses: A Robust, LowDiameter, LowLatency PeertoPeer Network
, 2003
"... A number of Distributed Hash Table (DHT)based protocols have been proposed to address the issue of scalability in peertopeer networks. However, it remains an open question whether there exists a DHT scheme that can achieve the theoretical lower bound of log log n on network diameter when the avera ..."
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Cited by 22 (1 self)
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A number of Distributed Hash Table (DHT)based protocols have been proposed to address the issue of scalability in peertopeer networks. However, it remains an open question whether there exists a DHT scheme that can achieve the theoretical lower bound of log log n on network diameter when the average routing table size at nodes is no more than log n. In this paper, we present Ulysses, a peertopeer network based on the butterfly topology that matches this theoretical lower bound. Compared to existing DHTbased schemes with similar routing table size, Ulysses reduces the network diameter by a factor of log log n, which is 24 for typical configurations. This translates into the same amount of reduction on query latency and average traffic per link/node. In addition, Ulysses maintains the same level of robustness in terms of routing in the face of faults and recovering from graceful/ungraceful joins/departures, as provided by existing DHTbased schemes. The protocol is formally verified for its correctness and robustness using techniques from distributed computing. The performance of the protocol has been evaluated using both analysis and simulation.
A Framework for Structured PeertoPeer Overlay Networks
 In Postproceedings of the Global Computing Conference, LNCS
, 2004
"... Structured peertopeer overlay networks have recently emerged as good candidate infrastructure for building novel largescale and robust Internet applications in which participating peers share computing resources as equals. In the past three year, various structured peertopeer overlay networks h ..."
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Cited by 16 (4 self)
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Structured peertopeer overlay networks have recently emerged as good candidate infrastructure for building novel largescale and robust Internet applications in which participating peers share computing resources as equals. In the past three year, various structured peertopeer overlay networks have been proposed, and probably more are to come. We present a framework for understanding, analyzing and designing structured peertopeer overlay networks. The main objective of the paper is to provide practical guidelines for the design of structured overlay networks by identifying a fundamental element in the construction of overlay networks: the embedding of kary trees. Then, a number of effective techniques for maintaining these overlay networks are discussed. The proposed framework has been effective in the development of the DKS system.
Practical Robust Communication in DHTs Tolerating a Byzantine Adversary
"... There are several analytical results on distributed hash tables (DHTs) that can tolerate Byzantine faults. Unfortunately, in such systems, critical operations such as data retrieval and message sending incur significant communication costs. For example, a simple scheme used in many Byzantine faultt ..."
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Cited by 14 (3 self)
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There are several analytical results on distributed hash tables (DHTs) that can tolerate Byzantine faults. Unfortunately, in such systems, critical operations such as data retrieval and message sending incur significant communication costs. For example, a simple scheme used in many Byzantine faulttolerant DHT constructions of n nodes requires O(log 3 n) messages; this is likely impractical for realworld applications. Currently, the best known message complexity is O(log 2 n) in expectation; however, the corresponding protocol suffers from prohibitive costs owing to hidden constants in the asymptotic notation and to setup costs. In this paper, we focus on reducing the communication costs against a computationally bounded adversary. We employ threshold cryptography and distributed key generation to define two protocols both of which are more efficient than existing solutions. In comparison, our first protocol is deterministic with O(log 2 n) message complexity and our second protocol is randomized with expected O(log n) message complexity. Further, both the hidden constants and setup costs for our protocols are small and no trusted third party is required. Finally, we present results from microbenchmarks conducted over PlanetLab showing that our protocols are practical for deployment under significant levels of churn and adversarial behaviour. 1.
The expansion and mixing time of skip graphs with applications
 In Proc. of the 17th ACM Symp. on Parallel Algorithms and Architectures (SPAA
, 2005
"... We prove that with high probability a skip graph contains a 4regular expander as a subgraph and estimate the quality of the expansion via simulations. As a consequence, skip graphs contain a large connected component even after an adversarial deletion of nodes. We show how the expansion property ca ..."
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We prove that with high probability a skip graph contains a 4regular expander as a subgraph and estimate the quality of the expansion via simulations. As a consequence, skip graphs contain a large connected component even after an adversarial deletion of nodes. We show how the expansion property can be used to sample a node in the skip graph in a highly efficient manner. We also show that the expansion property can be used to load balance the skip graph quickly. Finally, it is shown that the skip graph could serve as an unstructured P2P system, making it a good candidate for a hybrid P2P system. 1
Reducing Communication Costs in Robust PeertoPeer Networks
"... Several recent research results describe how to design Distributed Hash Tables (DHTs) that are robust to adversarial attack via Byzantine faults. Unfortunately, all of these results require a significant blowup in communication costs over standard DHTs. For example, to perform a lookup operation, al ..."
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Cited by 8 (2 self)
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Several recent research results describe how to design Distributed Hash Tables (DHTs) that are robust to adversarial attack via Byzantine faults. Unfortunately, all of these results require a significant blowup in communication costs over standard DHTs. For example, to perform a lookup operation, all such robust DHTs of which we are aware require sending O(log 3 n) messages while standard DHTs require sending only O(log n), where n is the number of nodes in the network. In this paper, we describe protocols to reduce the communication costs of all such robust DHTs. In particular, we give a protocol to reduce the number of messages sent to perform a lookup operation from O(log 3 n) to O(log 2 n) in expectation. Moreover, we also give a protocol for sending a large (i.e. containing Ω(log 4 n) bits) message securely through a robust DHT that requires, in expectation, only a constant blowup in the total number of bits sent compared with performing the same operation in a standard DHT. This is an improvement over the O(log 2 n) bit blowup that is required to perform such an operation in all current robust DHTs. Both of our protocols are robust against an adaptive adversary.
Scalable Byzantine Agreement
, 2004
"... This paper gives a scalable protocol for solving the Byzantine agreement problem. The protocol is scalable in the sense that for Byzantine agreement over n processors, each processor sends and receives only O(log n) messages in expectation. To the best of our knowledge this is the first result for t ..."
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This paper gives a scalable protocol for solving the Byzantine agreement problem. The protocol is scalable in the sense that for Byzantine agreement over n processors, each processor sends and receives only O(log n) messages in expectation. To the best of our knowledge this is the first result for the Byzantine agreement problem where each processor sends and receives o(n) messages. The protocol uses randomness and is correct with high probability. 1 It can tolerate any fraction of faulty processors which is strictly less than 1/6. Our result partially answers the following question posed by Kenneth Birman: “How scalable are the traditional solutions to problems such as Consensus or Byzantine Agreement? ” [5]. 1
FChord: Improved uniform routing on Chord
 Proc. 11th Colloquium on Structural Information and Communication Complexity
, 2004
"... We propose a family of novel Chordbased P2P schemes retaining all positive aspects that made Chord a popular topology for routing in P2P networks. The schemes, based on the Fibonacci number system, allow to simultaneously improve on the maximum/average number of hops for lookups and the routing tab ..."
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Cited by 5 (3 self)
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We propose a family of novel Chordbased P2P schemes retaining all positive aspects that made Chord a popular topology for routing in P2P networks. The schemes, based on the Fibonacci number system, allow to simultaneously improve on the maximum/average number of hops for lookups and the routing table size per node.
Routing Complexity of Faulty Networks
 In Proc. of 24th Annu. ACM Symp.on Principles of Distributed Computing (PODC ’05
, 2004
"... One of the fundamental problems in distributed computing is how to efficiently perform routing in a faulty network in which each link fails with some probability. This paper investigates how big the failure probability can be, before the capability to efficiently find a path in the network is lost. ..."
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One of the fundamental problems in distributed computing is how to efficiently perform routing in a faulty network in which each link fails with some probability. This paper investigates how big the failure probability can be, before the capability to efficiently find a path in the network is lost. Our main results show tight upper and lower bounds for the failure probability which permits routing, both for the hypercube and for the ddimensional mesh. We use tools from percolation theory to show that in the ddimensional mesh, once a giant component appears  efficient routing is possible. A different behavior is observed when the hypercube is considered. In the hypercube there is a range of failure probabilities in which short paths exist with high probability, yet finding them must involve querying essentially the entire network. Thus the routing complexity of the hypercube shows an asymptotic phase transition. The critical probability with respect to routing complexity lies in a different location then that of the critical probability with respect to connectivity. Finally we show that an oracle access to links (as opposed to local routing) may reduce significantly the complexity of the routing problem. We demonstrate this fact by providing tight upper and lower bounds for the complexity of routing in the random graph G n,p .
Experiences building security applications on DHTs
"... In the recent past we introduced two new security applications built on peertopeer systems and distributed hashtables (DHTs). First, we designed Adeona [18], which leverages DHTs to provide a privacypreserving laptop tracking solution. Second, we designed the Vanish [10] selfdestructing data sys ..."
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In the recent past we introduced two new security applications built on peertopeer systems and distributed hashtables (DHTs). First, we designed Adeona [18], which leverages DHTs to provide a privacypreserving laptop tracking solution. Second, we designed the Vanish [10] selfdestructing data system, which uses DHTs to protect against retroactive attacks on archived data in the cloud. Both systems exploit intuitive properties of DHTs that differentiate them from centralized solutions: e.g., complete or partial decentralization, giant scale, and geographic distribution. We implemented and made publicly available research prototypes of both Adeona and Vanish; the Adeona prototype uses OpenDHT as its underlying DHT and the Vanish prototype uses the Vuze DHT. While the properties of DHTs make them a tempting environment for new securitybased systems, existing DHTs were never designed to support security or privacy applications, and such applications therefore stress DHTs in new ways. This paper provides a retrospective from our collective experience both designing and prototyping the two DHTbased security/privacy applications, and operating and designing deployed DHTs (OpenDHT and Vuze). We discuss limitations and vulnerabilities of modern DHTs for security applications and propose very simple defenses that — perhaps surprisingly — greatly raise the bar for existing DHTs against certain privacy attacks. We also advocate for a hybrid approach that combines the best of both decentralized DHTs and centralized services for new security applications. Our goal is to inform the design of future DHTs and to strengthen the applicability of existing DHTs for supporting applications such as Adeona and Vanish. 1