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87
Secure and efficient asynchronous broadcast protocols (Extended Abstract)
 Advances in Cryptology: CRYPTO 2001
, 2001
"... Broadcast protocols are a fundamental building block for implementing replication in faulttolerant distributed systems. This paper addresses secure service replication in an asynchronous environment with a static set of servers, where a malicious adversary may corrupt up to a threshold of servers ..."
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Cited by 67 (19 self)
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Broadcast protocols are a fundamental building block for implementing replication in faulttolerant distributed systems. This paper addresses secure service replication in an asynchronous environment with a static set of servers, where a malicious adversary may corrupt up to a threshold of servers and controls the network. We develop a formal model using concepts from modern cryptography, give modular definitions for several broadcast problems, including reliable, atomic, and secure causal broadcast, and present protocols implementing them. Reliable broadcast is a basic primitive, also known as the Byzantine generals problem, providing agreement on a delivered message. Atomic broadcast imposes additionally a total order on all delivered messages. We present a randomized atomic broadcast protocol based on a new, efficient multivalued asynchronous Byzantine agreement primitive with an external validity condition. Apparently, no such efficient asynchronous atomic broadcast protocol maintaining liveness and safety in the Byzantine model has appeared previously in the literature. Secure causal broadcast extends atomic broadcast by encryption to guarantee a causal order among the delivered messages. Our protocols use threshold cryptography for signatures, encryption, and cointossing.
Heartbeat: A TimeoutFree Failure Detector for Quiescent Reliable Communication
, 1997
"... We study the problem of achieving reliable communication with quiescent algorithms (i.e., algorithms that eventually stop sending messages) in asynchronoussystems with process crashes and lossy links. We first show that it is impossible to solve this problem without failure detectors. We then show h ..."
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Cited by 51 (6 self)
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We study the problem of achieving reliable communication with quiescent algorithms (i.e., algorithms that eventually stop sending messages) in asynchronoussystems with process crashes and lossy links. We first show that it is impossible to solve this problem without failure detectors. We then show how to solve it using a new failure detector, called heartbeat. In contrast to previous failure detectors that have been used to circumvent impossibility results, the heartbeat failure detector is implementable, and its implementation does not use timeouts. These results have wide applicability: they can be used to transform many existing algorithms that tolerate only process crashes into quiescent algorithms that tolerate both process crashes and message losses. This can be applied to consensus, atomic broadcast, kset agreement, atomic commitment, etc. The heartbeat failure detector is novel: besides being implementable without timeouts, it does not output lists of suspects as typical failu...
Hundreds of Impossibility Results for Distributed Computing
 Distributed Computing
, 2003
"... We survey results from distributed computing that show tasks to be impossible, either outright or within given resource bounds, in various models. The parameters of the models considered include synchrony, faulttolerance, different communication media, and randomization. The resource bounds refe ..."
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Cited by 44 (4 self)
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We survey results from distributed computing that show tasks to be impossible, either outright or within given resource bounds, in various models. The parameters of the models considered include synchrony, faulttolerance, different communication media, and randomization. The resource bounds refer to time, space and message complexity. These results are useful in understanding the inherent difficulty of individual problems and in studying the power of different models of distributed computing.
Conditions on input vectors for consensus solvability in asynchronous distributed systems
 Journal of the ACM
, 2001
"... Abstract. This article introduces and explores the conditionbased approach to solve the consensus problem in asynchronous systems. The approach studies conditions that identify sets of input vectors for which it is possible to solve consensus despite the occurrence of up to f process crashes. The f ..."
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Cited by 36 (11 self)
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Abstract. This article introduces and explores the conditionbased approach to solve the consensus problem in asynchronous systems. The approach studies conditions that identify sets of input vectors for which it is possible to solve consensus despite the occurrence of up to f process crashes. The first main result defines acceptable conditions and shows that these are exactly the conditions for which a consensus protocol exists. Two examples of realistic acceptable conditions are presented, and proved to be maximal, in the sense that they cannot be extended and remain acceptable. The second main result is a generic consensus sharedmemory protocol for any acceptable condition. The protocol always guarantees agreement and validity, and terminates (at least) when the inputs satisfy the condition with which the protocol has been instantiated, or when there are no crashes. An efficient version of the protocol is then designed for the message passing model that works when f < n/2, and it is shown that no such protocol exists when f ≥ n/2. It is also shown how the protocol’s safety can be traded for its liveness.
A Simple Algorithmically Reasoned Characterization of Waitfree Computations
 In Proceedings of the 16th Annual ACM Symposium on Principles of Distributed Computing
, 1996
"... ) Elizabeth Borowsky (borowsky@hpl.hp.com) HewlettPackard Laboratories PaloAlto, CA 94303 U.S.A. Eli Gafni (eli@cs.ucla.edu) Computer Science Department University of California, Los Angeles Los Angeles, CA 90024 U.S.A. July 1, 1996 Abstract In a sequence of two pioneering papers Herlihy and S ..."
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Cited by 34 (11 self)
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) Elizabeth Borowsky (borowsky@hpl.hp.com) HewlettPackard Laboratories PaloAlto, CA 94303 U.S.A. Eli Gafni (eli@cs.ucla.edu) Computer Science Department University of California, Los Angeles Los Angeles, CA 90024 U.S.A. July 1, 1996 Abstract In a sequence of two pioneering papers Herlihy and Shavit characterized waitfree sharedmemory computations. The derivation of the characterization involves homology for the necessary conditions, and complex geometry arguments for the sufficiency. This paper gives an alternative proof of the conditions using familiar algorithmic arguments. Our only reliance on geometry is the use of a corollary to the simplicial approximation. Furthermore, this paper is the first to present another consequence of the relation between distributed algorithms and topology: that certain theorems in topology are naturally proven by distributed algorithms interpretations. Our techniques can be extended to characterize models that are more complex than the waitfree...
The BG distributed simulation algorithm
, 1997
"... A snapshot shared memory algorithm is presented, allowing a set off+1processes, anyfof which may exhibit stopping failures, to “simulate ” a larger numbernof processes, also with at mostffailures. One application of this simulation algorithm is to convert an arbitrarykfaulttolerantnprocess soluti ..."
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Cited by 33 (12 self)
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A snapshot shared memory algorithm is presented, allowing a set off+1processes, anyfof which may exhibit stopping failures, to “simulate ” a larger numbernof processes, also with at mostffailures. One application of this simulation algorithm is to convert an arbitrarykfaulttolerantnprocess solution for theksetagreement problem into a waitfreek+1process solution for the same problem. Since thek+1process ksetagreement problem has been shown to have no waitfree solution [4, 16, 24], this transformation implies that there is nokfaulttolerant solution to thenprocessksetagreement problem, for anyn. More generally, the algorithm satisfies the requirements of a faulttolerant distributed simulation. The distributed simulation implements a notion of faulttolerant reducibility between decision problems. These notions are defined, and examples of their use are provided. The algorithm is presented and verified in terms of I/O automata. The presentation has a great deal of interesting modularity, expressed by I/O automaton composition and both forward and backward simulation relations. Composition is used to include a safe agreement module as a subroutine. Forward and backward simulation relations are used to view the algorithm as implementing a multitry snapshot strategy. The main algorithm works in snapshot shared memory systems; a simple modification of the algorithm that works in read/write shared memory systems is also presented.
Algebraic spans
, 2000
"... Topological methods have yielded a variety of lower bounds and impossibility results for distributed computing. In this paper, we introduce a new tool for proving impossibility results, which is based on a core theorem of algebraic topology, the acyclic carrier theorem, and unifies, generalizes and ..."
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Cited by 32 (16 self)
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Topological methods have yielded a variety of lower bounds and impossibility results for distributed computing. In this paper, we introduce a new tool for proving impossibility results, which is based on a core theorem of algebraic topology, the acyclic carrier theorem, and unifies, generalizes and extends earlier results.
On Quiescent Reliable Communication
, 1998
"... We study the problem of achieving reliable communication with quiescent algorithms (i.e., algorithms that eventually stop sending messages) in asynchronous systems with process crashes and lossy links. We first show that it is impossible to solve this problem in purely asynchronous systems (with n ..."
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Cited by 27 (1 self)
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We study the problem of achieving reliable communication with quiescent algorithms (i.e., algorithms that eventually stop sending messages) in asynchronous systems with process crashes and lossy links. We first show that it is impossible to solve this problem in purely asynchronous systems (with no failure detectors). We then show that, among failure detectors that output lists of suspects, the weakest one that can be used to solve this problem is 3P , a failure detector that cannot be implemented. To overcome this difficulty, we introduce an implementable failure detector called Heartbeat and show that it can be used to achieve quiescent reliable communication. Heartbeat is novel: in contrast to typical failure detectors, it does not output lists of suspects and it is implementable without timeouts. With Heartbeat, many existing algorithms that tolerate only process crashes can be transformed into quiescent algorithms that tolerate both process crashes and message losses. Thi...
Homotopy and Concurrency
 Bulletin of the EATCS
, 1994
"... In this paper we give a homotopy theoretic proof of a wellknown result in database engineering: that 2phase locking is safe. The proof gives an immediate intuitive reason for why the 2phase locking condition implies safety. We point out a number of interesting open questions regarding the interpl ..."
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Cited by 26 (1 self)
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In this paper we give a homotopy theoretic proof of a wellknown result in database engineering: that 2phase locking is safe. The proof gives an immediate intuitive reason for why the 2phase locking condition implies safety. We point out a number of interesting open questions regarding the interplay between homotopy and concurrency. Keywords: Homotopy theory, serializability, 2phase locking, concurrency theory 1 Introduction What has homotopy got to do with concurrency? At first sight it seems unlikely that there should be any relationship between these two subjects. After all, homotopy theory is about continuous objects while concurrency typically deals with discrete structures. In this paper I will try to show that, on the contrary, there may be a very natural relationship between the two. Instead of making a lot of abstract statements about homotopy and concurrency I would like to work through the proof of a theorem which all database engineers learn at their Mother's knee: th...
The Combinatorial Structure of Waitfree Solvable Tasks (Extended Abstract)
, 1996
"... This paper presents a selfcontained study of waitfree solvable tasks. A new necessary and sufficient condition for waitfree solvability is proved, providing a characterization of the waitfree solvable tasks. The necessary condition is used to prove tight bounds on renaming and kset consensus. ..."
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Cited by 24 (13 self)
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This paper presents a selfcontained study of waitfree solvable tasks. A new necessary and sufficient condition for waitfree solvability is proved, providing a characterization of the waitfree solvable tasks. The necessary condition is used to prove tight bounds on renaming and kset consensus. The framework is based on topology, but uses only elementary combinatorics, and does not rely on algebraic or geometric arguments.