5 Search Results for "Dolev, Danny"

Document
Track A: Algorithms, Complexity and Games
DOI: 10.4230/LIPIcs.ICALP.2024.37
Fast Approximate Counting of Cycles

Authors: Keren Censor-Hillel, Tomer Even, and Virginia Vassilevska Williams

Published in: LIPIcs, Volume 297, 51st International Colloquium on Automata, Languages, and Programming (ICALP 2024)

Abstract
We consider the problem of approximate counting of triangles and longer fixed length cycles in directed graphs. For triangles, Tětek [ICALP'22] gave an algorithm that returns a (1±ε)-approximation in Õ(n^ω/t^{ω-2}) time, where t is the unknown number of triangles in the given n node graph and ω < 2.372 is the matrix multiplication exponent. We obtain an improved algorithm whose running time is, within polylogarithmic factors the same as that for multiplying an n× n/t matrix by an n/t × n matrix. We then extend our framework to obtain the first nontrivial (1± ε)-approximation algorithms for the number of h-cycles in a graph, for any constant h ≥ 3. Our running time is Õ(MM(n,n/t^{1/(h-2)},n)), the time to multiply n × n/(t^{1/(h-2)}) by n/(t^{1/(h-2)) × n matrices. Finally, we show that under popular fine-grained hypotheses, this running time is optimal.
Cite as

Keren Censor-Hillel, Tomer Even, and Virginia Vassilevska Williams. Fast Approximate Counting of Cycles. In 51st International Colloquium on Automata, Languages, and Programming (ICALP 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 297, pp. 37:1-37:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{censorhillel_et_al:LIPIcs.ICALP.2024.37,
  author =	{Censor-Hillel, Keren and Even, Tomer and Vassilevska Williams, Virginia},
  title =	{{Fast Approximate Counting of Cycles}},
  booktitle =	{51st International Colloquium on Automata, Languages, and Programming (ICALP 2024)},
  pages =	{37:1--37:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-322-5},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{297},
  editor =	{Bringmann, Karl and Grohe, Martin and Puppis, Gabriele and Svensson, Ola},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2024.37},
  URN =		{urn:nbn:de:0030-drops-201809},
  doi =		{10.4230/LIPIcs.ICALP.2024.37},
  annote =	{Keywords: Approximate triangle counting, Approximate cycle counting Fast matrix multiplication, Fast rectangular matrix multiplication}
}
Document
DOI: 10.4230/LIPIcs.DISC.2023.1
Colordag: An Incentive-Compatible Blockchain

Authors: Ittai Abraham, Danny Dolev, Ittay Eyal, and Joseph Y. Halpern

Published in: LIPIcs, Volume 281, 37th International Symposium on Distributed Computing (DISC 2023)

Abstract
We present Colordag, a blockchain protocol where following the prescribed strategy is, with high probability, a best response as long as all miners have less than 1/2 of the mining power. We prove the correctness of Colordag even if there is an extremely powerful adversary who knows future actions of the scheduler: specifically, when agents will generate blocks and when messages will arrive. The state-of-the-art protocol, Fruitchain, is an ε-Nash equilibrium as long as all miners have less than 1/2 of the mining power. However, there is a simple deviation that guarantees that deviators are never worse off than they would be by following Fruitchain, and can sometimes do better. Thus, agents are motivated to deviate. Colordag implements a solution concept that we call ε-sure Nash equilibrium and does not suffer from this problem. Because it is an ε-sure Nash equilibrium, Colordag is an ε-Nash equilibrium and with probability 1-ε is a best response.
Cite as

Ittai Abraham, Danny Dolev, Ittay Eyal, and Joseph Y. Halpern. Colordag: An Incentive-Compatible Blockchain. In 37th International Symposium on Distributed Computing (DISC 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 281, pp. 1:1-1:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{abraham_et_al:LIPIcs.DISC.2023.1,
  author =	{Abraham, Ittai and Dolev, Danny and Eyal, Ittay and Halpern, Joseph Y.},
  title =	{{Colordag: An Incentive-Compatible Blockchain}},
  booktitle =	{37th International Symposium on Distributed Computing (DISC 2023)},
  pages =	{1:1--1:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-301-0},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{281},
  editor =	{Oshman, Rotem},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2023.1},
  URN =		{urn:nbn:de:0030-drops-191272},
  doi =		{10.4230/LIPIcs.DISC.2023.1},
  annote =	{Keywords: Game theory, incentives, blockchain}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2022.38
Brief Announcement: Authenticated Consensus in Synchronous Systems with Mixed Faults

Authors: Ittai Abraham, Danny Dolev, Alon Kagan, and Gilad Stern

Published in: LIPIcs, Volume 246, 36th International Symposium on Distributed Computing (DISC 2022)

Abstract
Protocols solving authenticated consensus in synchronous networks with Byzantine faults have been widely researched and known to exists if and only if n > 2f for f Byzantine faults. Similarly, protocols solving authenticated consensus in partially synchronous networks are known to exist if n > 3f+2k for f Byzantine faults and k crash faults. In this work we fill a natural gap in our knowledge by presenting MixSync, an authenticated consensus protocol in synchronous networks resilient to f Byzantine faults and k crash faults if n > 2f+k. As a basic building block, we first define and then construct a publicly verifiable crusader agreement protocol with the same resilience. The protocol uses a simple double-send round to guarantee non-equivocation, a technique later used in the MixSync protocol. We then discuss how to construct a state machine replication protocol using these ideas, and how they can be used in general to make such protocols resilient to crash faults. Finally, we prove lower bounds showing that n > 2f+k is optimally resilient for consensus and state machine replication protocols.
Cite as

Ittai Abraham, Danny Dolev, Alon Kagan, and Gilad Stern. Brief Announcement: Authenticated Consensus in Synchronous Systems with Mixed Faults. In 36th International Symposium on Distributed Computing (DISC 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 246, pp. 38:1-38:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{abraham_et_al:LIPIcs.DISC.2022.38,
  author =	{Abraham, Ittai and Dolev, Danny and Kagan, Alon and Stern, Gilad},
  title =	{{Brief Announcement: Authenticated Consensus in Synchronous Systems with Mixed Faults}},
  booktitle =	{36th International Symposium on Distributed Computing (DISC 2022)},
  pages =	{38:1--38:3},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-255-6},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{246},
  editor =	{Scheideler, Christian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2022.38},
  URN =		{urn:nbn:de:0030-drops-172292},
  doi =		{10.4230/LIPIcs.DISC.2022.38},
  annote =	{Keywords: consensus, state machine replication, mixed faults, synchrony, lower bounds}
}
Document
Invited Talk
DOI: 10.4230/OASIcs.Tokenomics.2021.1
Distributed Computing Meets Game Theory: Fault Tolerance and Implementation with Cheap Talk (Invited Talk)

Authors: Joseph Y. Halpern

Published in: OASIcs, Volume 97, 3rd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2021)

Abstract
Traditionally, work in distributed computing has divided the agents into "good guys" and "bad guys". The good guys follow the protocol; the bad guys do everything in their power to make sure it does not work. By way of contrast, game theory has focused on "rational" agents, who try to maximize their utilities. Here I try to combine these viewpoints. Specifically, following the work of Abraham et al. [I. Abraham et al., 2006], I consider (k,t)-robust protocols/strategies, which tolerate coalitions of rational players of size up to k and up to t malicious players. I focus in particular on the problem that economists have called implementing a mediator. That is, can the players in the system, just talking among themselves (using what economists call "cheap talk") simulate the effects of the mediator (see, e.g., [I. Barany, 1992; E. Ben-Porath, 2003; Forges, 1990; D. Gerardi, 2004; Y. Heller, 2005; A. Urbano and J. E. Vila, 2002; A. Urbano and J. E. Vila, 2004]). In computer science, this essentially amounts to multiparty computation [O. Goldreich et al., 1987; A. Shamir et al., 1981; A. Yao, 1982]. Ideas from cryptography and distributed computing allow us to prove results on how many agents are required to implement a (k,t)-robust mediator just using cheap talk. These results subsume (and, in some cases, correct) results from the game theory literature. The results of Abraham et al. [I. Abraham et al., 2006] were proved for what are called synchronous systems in the distributed computing community; this is also the case for all the results in the economics literature cited above. In synchronous systems, communication proceeds in atomic rounds, and all messages sent during round r are received by round r + 1. But many systems in the real world are asynchronous. In an asynchronous setting, there are no rounds; messages sent by the players may take arbitrarily long to get to their recipients. Markets and the internet are best viewed as asynchronous. Blockchain implementations assume partial synchrony, where there is an upper bound on how long messages take to arrive. The partial synchronous setting already shows some of the difficulty of moving away from synchrony: An agent i can wait to take its action until it receives a message from j (on which its action can depend). This cannot happen in a synchronous setting. Abraham, Dolev, Geffner, abnd Halpern [I. Abraham et al., 2019] extend the results on implementing mediators to the asynchronous setting.
Cite as

Joseph Y. Halpern. Distributed Computing Meets Game Theory: Fault Tolerance and Implementation with Cheap Talk (Invited Talk). In 3rd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2021). Open Access Series in Informatics (OASIcs), Volume 97, pp. 1:1-1:2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{halpern:OASIcs.Tokenomics.2021.1,
  author =	{Halpern, Joseph Y.},
  title =	{{Distributed Computing Meets Game Theory: Fault Tolerance and Implementation with Cheap Talk}},
  booktitle =	{3rd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2021)},
  pages =	{1:1--1:2},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-220-4},
  ISSN =	{2190-6807},
  year =	{2022},
  volume =	{97},
  editor =	{Gramoli, Vincent and Halaburda, Hanna and Pass, Rafael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.Tokenomics.2021.1},
  URN =		{urn:nbn:de:0030-drops-158981},
  doi =		{10.4230/OASIcs.Tokenomics.2021.1},
  annote =	{Keywords: robust equilibrium, implementing mediators, asynchronous systems}
}
Document
DOI: 10.4230/DagSemRep.138
Time Services (Dagstuhl Seminar 9611)

Authors: Danny Dolev, Rüdiger Reischuk, Fred B. Schneider, and H. Raymond Strong

Published in: Dagstuhl Seminar Reports. Dagstuhl Seminar Reports, Volume 1 (2021)

Abstract
Cite as

Danny Dolev, Rüdiger Reischuk, Fred B. Schneider, and H. Raymond Strong. Time Services (Dagstuhl Seminar 9611). Dagstuhl Seminar Report 138, pp. 1-19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (1996)

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@TechReport{dolev_et_al:DagSemRep.138,
  author =	{Dolev, Danny and Reischuk, R\"{u}diger and Schneider, Fred B. and Strong, H. Raymond},
  title =	{{Time Services (Dagstuhl Seminar 9611)}},
  pages =	{1--19},
  ISSN =	{1619-0203},
  year =	{1996},
  type = 	{Dagstuhl Seminar Report},
  number =	{138},
  institution =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemRep.138},
  URN =		{urn:nbn:de:0030-drops-150256},
  doi =		{10.4230/DagSemRep.138},
}
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