20 Search Results for "Abraham, Ittai"

Document
DOI: 10.4230/LIPIcs.OPODIS.2023.14
Fever: Optimal Responsive View Synchronisation

Authors: Andrew Lewis-Pye and Ittai Abraham

Published in: LIPIcs, Volume 286, 27th International Conference on Principles of Distributed Systems (OPODIS 2023)

Abstract
View synchronisation is an important component of many modern Byzantine Fault Tolerant State Machine Replication (SMR) systems in the partial synchrony model. Roughly, the efficiency of view synchronisation is measured as the word complexity and latency required for moving from being synchronised in a view of one correct leader to being synchronised in the view of the next correct leader. The efficiency of view synchronisation has emerged as a major bottleneck in the efficiency of SMR systems as a whole. A key question remained open: Do there exist view synchronisation protocols with asymptotically optimal quadratic worst-case word complexity that also obtain linear complexity and responsiveness when moving between consecutive correct leaders? We answer this question affirmatively with a new view synchronisation protocol for partial synchrony assuming partial initial clock synchronisation, called Fever. If n is the number of processors and t is the largest integer < n/3, then Fever has resilience t, and in all executions with at most 0 ≤ f ≤ t Byzantine parties and network delays of at most δ ≤ Δ after GST (where f and δ are unknown), Fever has worst-case word complexity O(fn+n) and worst-case latency O(Δ f + δ).
Cite as

Andrew Lewis-Pye and Ittai Abraham. Fever: Optimal Responsive View Synchronisation. In 27th International Conference on Principles of Distributed Systems (OPODIS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 286, pp. 14:1-14:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{lewispye_et_al:LIPIcs.OPODIS.2023.14,
  author =	{Lewis-Pye, Andrew and Abraham, Ittai},
  title =	{{Fever: Optimal Responsive View Synchronisation}},
  booktitle =	{27th International Conference on Principles of Distributed Systems (OPODIS 2023)},
  pages =	{14:1--14:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-308-9},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{286},
  editor =	{Bessani, Alysson and D\'{e}fago, Xavier and Nakamura, Junya and Wada, Koichi and Yamauchi, Yukiko},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2023.14},
  URN =		{urn:nbn:de:0030-drops-195041},
  doi =		{10.4230/LIPIcs.OPODIS.2023.14},
  annote =	{Keywords: Distributed Systems, State Machine Replication}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2023.29
On the Round Complexity of Asynchronous Crusader Agreement

Authors: Ittai Abraham, Naama Ben-David, Gilad Stern, and Sravya Yandamuri

Published in: LIPIcs, Volume 286, 27th International Conference on Principles of Distributed Systems (OPODIS 2023)

Abstract
We present new lower and upper bounds on the number of communication rounds required for asynchronous Crusader Agreement (CA) and Binding Crusader Agreement (BCA), two primitives that are used for solving binary consensus. We show results for the information theoretic and authenticated settings. In doing so, we present a generic model for proving round complexity lower bounds in the asynchronous setting. In some settings, our attempts to prove lower bounds on round complexity fail. Instead, we show new, tight, rather surprising round complexity upper bounds for Byzantine fault tolerant BCA with and without a PKI setup.
Cite as

Ittai Abraham, Naama Ben-David, Gilad Stern, and Sravya Yandamuri. On the Round Complexity of Asynchronous Crusader Agreement. In 27th International Conference on Principles of Distributed Systems (OPODIS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 286, pp. 29:1-29:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{abraham_et_al:LIPIcs.OPODIS.2023.29,
  author =	{Abraham, Ittai and Ben-David, Naama and Stern, Gilad and Yandamuri, Sravya},
  title =	{{On the Round Complexity of Asynchronous Crusader Agreement}},
  booktitle =	{27th International Conference on Principles of Distributed Systems (OPODIS 2023)},
  pages =	{29:1--29:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-308-9},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{286},
  editor =	{Bessani, Alysson and D\'{e}fago, Xavier and Nakamura, Junya and Wada, Koichi and Yamauchi, Yukiko},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2023.29},
  URN =		{urn:nbn:de:0030-drops-195195},
  doi =		{10.4230/LIPIcs.OPODIS.2023.29},
  annote =	{Keywords: lower bounds, asynchronous protocols, round complexity}
}
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
DOI: 10.4230/LIPIcs.OPODIS.2022.16
New Dolev-Reischuk Lower Bounds Meet Blockchain Eclipse Attacks

Authors: Ittai Abraham and Gilad Stern

Published in: LIPIcs, Volume 253, 26th International Conference on Principles of Distributed Systems (OPODIS 2022)

Abstract
In 1985, Dolev and Reischuk proved a fundamental communication lower bounds on protocols achieving fault tolerant synchronous broadcast and consensus: any deterministic protocol solving those tasks (even against omission faults) requires at least a quadratic number of messages to be sent by nonfaulty parties. In contrast, many blockchain systems achieve consensus with seemingly linear communication per instance against Byzantine faults. We explore this dissonance in three main ways. First, we extend the Dolev-Reischuk family of lower bounds and prove a new lower bound for Crusader Broadcast protocols. Our lower bound for crusader broadcast requires non-trivial extensions and a much stronger Byzantine adversary with the ability to simulate honest parties. Secondly, we extend our lower bounds to all-but-m Crusader Broadcast, in which up to m parties are allowed to output a different value. Finally, we discuss the ways in which these lower bounds relate to the security of blockchain systems. We show how Eclipse-style attacks in such systems can be viewed as specific instances of the attacks used in our lower bound for Crusader Broadcast. This connection suggests a more systematic way of analyzing and reasoning about Eclipse-style attacks through the lens of the Dolev-Reischuk family of attacks.
Cite as

Ittai Abraham and Gilad Stern. New Dolev-Reischuk Lower Bounds Meet Blockchain Eclipse Attacks. In 26th International Conference on Principles of Distributed Systems (OPODIS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 253, pp. 16:1-16:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{abraham_et_al:LIPIcs.OPODIS.2022.16,
  author =	{Abraham, Ittai and Stern, Gilad},
  title =	{{New Dolev-Reischuk Lower Bounds Meet Blockchain Eclipse Attacks}},
  booktitle =	{26th International Conference on Principles of Distributed Systems (OPODIS 2022)},
  pages =	{16:1--16:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-265-5},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{253},
  editor =	{Hillel, Eshcar and Palmieri, Roberto and Rivi\`{e}re, Etienne},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2022.16},
  URN =		{urn:nbn:de:0030-drops-176368},
  doi =		{10.4230/LIPIcs.OPODIS.2022.16},
  annote =	{Keywords: consensus, crusader broadcast, Byzantine fault tolerance, blockchain, synchrony, lower bounds}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2022.24
Communication-Efficient BFT Using Small Trusted Hardware to Tolerate Minority Corruption

Authors: Sravya Yandamuri, Ittai Abraham, Kartik Nayak, and Michael K. Reiter

Published in: LIPIcs, Volume 253, 26th International Conference on Principles of Distributed Systems (OPODIS 2022)

Abstract
Agreement protocols for partially synchronous networks tolerate fewer than one-third Byzantine faults. If parties are equipped with trusted hardware that prevents equivocation, then fault tolerance can be improved to fewer than one-half Byzantine faults, but typically at the cost of increased communication complexity. In this work, we present results that use small trusted hardware without worsening communication complexity assuming the adversary controls a fraction of the network that is less than one-half. In particular, we show a version of HotStuff that retains linear communication complexity in each view, leveraging trusted hardware to tolerate a minority of corruptions. Our result uses expander graph techniques to achieve efficient communication in a manner that may be of independent interest.
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Sravya Yandamuri, Ittai Abraham, Kartik Nayak, and Michael K. Reiter. Communication-Efficient BFT Using Small Trusted Hardware to Tolerate Minority Corruption. In 26th International Conference on Principles of Distributed Systems (OPODIS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 253, pp. 24:1-24:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{yandamuri_et_al:LIPIcs.OPODIS.2022.24,
  author =	{Yandamuri, Sravya and Abraham, Ittai and Nayak, Kartik and Reiter, Michael K.},
  title =	{{Communication-Efficient BFT Using Small Trusted Hardware to Tolerate Minority Corruption}},
  booktitle =	{26th International Conference on Principles of Distributed Systems (OPODIS 2022)},
  pages =	{24:1--24:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-265-5},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{253},
  editor =	{Hillel, Eshcar and Palmieri, Roberto and Rivi\`{e}re, Etienne},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2022.24},
  URN =		{urn:nbn:de:0030-drops-176448},
  doi =		{10.4230/LIPIcs.OPODIS.2022.24},
  annote =	{Keywords: communication complexity, consensus, trusted hardware}
}
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-dev.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
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2022.39
Brief Announcement: It’s not easy to relax: liveness in chained BFT protocols

Authors: Ittai Abraham, Natacha Crooks, Neil Giridharan, Heidi Howard, and Florian Suri-Payer

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

Abstract
Modern chained BFT SMR protocols have poor liveness under failures as they require multiple consecutive honest leaders to commit a single block. Siesta, our proposed new BFT SMR protocol, is instead able to commit a block that spans multiple non-consecutive honest leaders. Siesta reduces the expected commit latency of HotStuff by a factor of three under failures, and the worst-case latency by a factor of eight.
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Ittai Abraham, Natacha Crooks, Neil Giridharan, Heidi Howard, and Florian Suri-Payer. Brief Announcement: It’s not easy to relax: liveness in chained BFT protocols. In 36th International Symposium on Distributed Computing (DISC 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 246, pp. 39:1-39:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{abraham_et_al:LIPIcs.DISC.2022.39,
  author =	{Abraham, Ittai and Crooks, Natacha and Giridharan, Neil and Howard, Heidi and Suri-Payer, Florian},
  title =	{{Brief Announcement: It’s not easy to relax: liveness in chained BFT protocols}},
  booktitle =	{36th International Symposium on Distributed Computing (DISC 2022)},
  pages =	{39:1--39:3},
  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-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2022.39},
  URN =		{urn:nbn:de:0030-drops-172305},
  doi =		{10.4230/LIPIcs.DISC.2022.39},
  annote =	{Keywords: Consensus, blockchain, BFT}
}
Document
Invited Talk
DOI: 10.4230/OASIcs.FAB.2022.1
Reflections on the Past, Present and Future of Blockchain Foundations and Applications (Invited Talk)

Authors: Ittai Abraham

Published in: OASIcs, Volume 101, 5th International Symposium on Foundations and Applications of Blockchain 2022 (FAB 2022)

Abstract
We survey some of the amazing progress in Blockchain technology in the last 5 years: from foundations like consensus protocols, execution models, and zero-knowledge proofs, to why these foundations are critical for applications like decentralized finance and web3. The main part of the talk will try to envision the future of Blockchains: how will the "Endgame" look like? What foundations are we still missing? We argue that for Blockchains to thrive and reach Billions of users, we should expect a much more regulated landscape to emerge and discuss some exciting opportunities in reg-crypto and RegDeFi. An example of this direction is our new work on UTT which is a decentralized Ecash system with accountable privacy.
Cite as

Ittai Abraham. Reflections on the Past, Present and Future of Blockchain Foundations and Applications (Invited Talk). In 5th International Symposium on Foundations and Applications of Blockchain 2022 (FAB 2022). Open Access Series in Informatics (OASIcs), Volume 101, p. 1:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{abraham:OASIcs.FAB.2022.1,
  author =	{Abraham, Ittai},
  title =	{{Reflections on the Past, Present and Future of Blockchain Foundations and Applications}},
  booktitle =	{5th International Symposium on Foundations and Applications of Blockchain 2022 (FAB 2022)},
  pages =	{1:1--1:1},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-248-8},
  ISSN =	{2190-6807},
  year =	{2022},
  volume =	{101},
  editor =	{Tucci-Piergiovanni, Sara and Crooks, Natacha},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/OASIcs.FAB.2022.1},
  URN =		{urn:nbn:de:0030-drops-162686},
  doi =		{10.4230/OASIcs.FAB.2022.1},
  annote =	{Keywords: Blockchain}
}
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-dev.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/LIPIcs.OPODIS.2021.5
Good-Case and Bad-Case Latency of Unauthenticated Byzantine Broadcast: A Complete Categorization

Authors: Ittai Abraham, Ling Ren, and Zhuolun Xiang

Published in: LIPIcs, Volume 217, 25th International Conference on Principles of Distributed Systems (OPODIS 2021)

Abstract
This paper studies the good-case latency of unauthenticated Byzantine fault-tolerant broadcast, which measures the time it takes for all non-faulty parties to commit given a non-faulty broadcaster. For both asynchrony and synchrony, we show that n ≥ 4f is the tight resilience threshold that separates good-case 2 rounds and 3 rounds. For asynchronous Byzantine reliable broadcast (BRB), we also investigate the bad-case latency for all non-faulty parties to commit when the broadcaster is faulty but some non-faulty party commits. We provide matching upper and lower bounds on the resilience threshold of bad-case latency for BRB protocols with optimal good-case latency of 2 rounds. In particular, we show 2 impossibility results and propose 4 asynchronous BRB protocols.
Cite as

Ittai Abraham, Ling Ren, and Zhuolun Xiang. Good-Case and Bad-Case Latency of Unauthenticated Byzantine Broadcast: A Complete Categorization. In 25th International Conference on Principles of Distributed Systems (OPODIS 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 217, pp. 5:1-5:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{abraham_et_al:LIPIcs.OPODIS.2021.5,
  author =	{Abraham, Ittai and Ren, Ling and Xiang, Zhuolun},
  title =	{{Good-Case and Bad-Case Latency of Unauthenticated Byzantine Broadcast: A Complete Categorization}},
  booktitle =	{25th International Conference on Principles of Distributed Systems (OPODIS 2021)},
  pages =	{5:1--5:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-219-8},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{217},
  editor =	{Bramas, Quentin and Gramoli, Vincent and Milani, Alessia},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2021.5},
  URN =		{urn:nbn:de:0030-drops-157806},
  doi =		{10.4230/LIPIcs.OPODIS.2021.5},
  annote =	{Keywords: Byzantine broadcast, asynchrony, synchrony, latency, good-case, optimal}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2021.27
Optimal Good-Case Latency for Rotating Leader Synchronous BFT

Authors: Ittai Abraham, Kartik Nayak, and Nibesh Shrestha

Published in: LIPIcs, Volume 217, 25th International Conference on Principles of Distributed Systems (OPODIS 2021)

Abstract
This paper explores the good-case latency of synchronous Byzantine Fault Tolerant (BFT) consensus protocols in the rotating leader setting. We first present a lower bound that relates the latency of a broadcast when the sender is honest and the latency of switching to the next sender. We then present a matching upper bound with a latency of 2Δ (Δ is the pessimistic synchronous delay) with an optimistically responsive change to the next sender. The results imply that both our lower and upper bounds are tight. We implement and evaluate our protocol and show that our protocol obtains similar latency compared to state-of-the-art stable-leader protocol Sync HotStuff while allowing optimistically responsive leader rotation.
Cite as

Ittai Abraham, Kartik Nayak, and Nibesh Shrestha. Optimal Good-Case Latency for Rotating Leader Synchronous BFT. In 25th International Conference on Principles of Distributed Systems (OPODIS 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 217, pp. 27:1-27:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{abraham_et_al:LIPIcs.OPODIS.2021.27,
  author =	{Abraham, Ittai and Nayak, Kartik and Shrestha, Nibesh},
  title =	{{Optimal Good-Case Latency for Rotating Leader Synchronous BFT}},
  booktitle =	{25th International Conference on Principles of Distributed Systems (OPODIS 2021)},
  pages =	{27:1--27:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-219-8},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{217},
  editor =	{Bramas, Quentin and Gramoli, Vincent and Milani, Alessia},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2021.27},
  URN =		{urn:nbn:de:0030-drops-158022},
  doi =		{10.4230/LIPIcs.OPODIS.2021.27},
  annote =	{Keywords: Distributed Computing, Byzantine Fault Tolerance, Synchrony}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2021.62
Brief Announcement: Communication-Efficient BFT Using Small Trusted Hardware to Tolerate Minority Corruption

Authors: Sravya Yandamuri, Ittai Abraham, Kartik Nayak, and Michael Reiter

Published in: LIPIcs, Volume 209, 35th International Symposium on Distributed Computing (DISC 2021)

Abstract
Small trusted hardware primitives can improve fault tolerance of Byzantine Fault Tolerant (BFT) protocols to one-half faults. However, existing works achieve this at the cost of increased communication complexity. In this work, we explore the design of communication-efficient BFT protocols that can boost fault tolerance to one-half without worsening communication complexity. Our results include a version of HotStuff that retains linear communication complexity in each view and a version of the VABA protocol with quadratic communication, both leveraging trusted hardware to tolerate a minority of corruptions. As a building block, we present communication-efficient provable broadcast, a core broadcast primitive with increased fault tolerance. Our results use expander graphs to achieve efficient communication in a manner that may be of independent interest.
Cite as

Sravya Yandamuri, Ittai Abraham, Kartik Nayak, and Michael Reiter. Brief Announcement: Communication-Efficient BFT Using Small Trusted Hardware to Tolerate Minority Corruption. In 35th International Symposium on Distributed Computing (DISC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 209, pp. 62:1-62:4, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{yandamuri_et_al:LIPIcs.DISC.2021.62,
  author =	{Yandamuri, Sravya and Abraham, Ittai and Nayak, Kartik and Reiter, Michael},
  title =	{{Brief Announcement: Communication-Efficient BFT Using Small Trusted Hardware to Tolerate Minority Corruption}},
  booktitle =	{35th International Symposium on Distributed Computing (DISC 2021)},
  pages =	{62:1--62:4},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-210-5},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{209},
  editor =	{Gilbert, Seth},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2021.62},
  URN =		{urn:nbn:de:0030-drops-148647},
  doi =		{10.4230/LIPIcs.DISC.2021.62},
  annote =	{Keywords: communication complexity, consensus, trusted hardware}
}
Document
Invited Talk
DOI: 10.4230/OASIcs.Tokenomics.2020.2
When Nakamoto Meets Nash: Blockchain Breakthrough Through the Lens of Game Theory (Invited Talk)

Authors: Ittai Abraham

Published in: OASIcs, Volume 82, 2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020)

Abstract
We discuss the deep connections between Blockchain Technology, Computer Science and Economics. The talk surveys the ways the Blockchain disruption raises fundamental challenges that have a deep game theoretic nature. We focus on four major open questions: 1) The need for a game theoretic endogenous theory of the utility of Money Systems that can model friction, fairness, and trust. 2) The need to incentivize trust in both consensus and execution. A need for a game theoretic theory of Consensus and analogue to Byzantine Fault Tolerance. A need for a game theoretic framework for scalable validation. 3) The challenge of incentivizing fairness and chain quality. Can we use notions of robust equilibrium to provide better notions of fairness? 4) The open question of how Blockchains can incentivise welfare. The need for a theory of Blockchains as public goods.
Cite as

Ittai Abraham. When Nakamoto Meets Nash: Blockchain Breakthrough Through the Lens of Game Theory (Invited Talk). In 2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020). Open Access Series in Informatics (OASIcs), Volume 82, p. 2:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{abraham:OASIcs.Tokenomics.2020.2,
  author =	{Abraham, Ittai},
  title =	{{When Nakamoto Meets Nash: Blockchain Breakthrough Through the Lens of Game Theory}},
  booktitle =	{2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020)},
  pages =	{2:1--2:1},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-157-3},
  ISSN =	{2190-6807},
  year =	{2021},
  volume =	{82},
  editor =	{Anceaume, Emmanuelle and Bisi\`{e}re, Christophe and Bouvard, Matthieu and Bramas, Quentin and Casamatta, Catherine},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/OASIcs.Tokenomics.2020.2},
  URN =		{urn:nbn:de:0030-drops-135248},
  doi =		{10.4230/OASIcs.Tokenomics.2020.2},
  annote =	{Keywords: Game theory, Consensus, Blockchain}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2020.11
Information Theoretic HotStuff

Authors: Ittai Abraham and Gilad Stern

Published in: LIPIcs, Volume 184, 24th International Conference on Principles of Distributed Systems (OPODIS 2020)

Abstract
This work presents Information Theoretic HotStuff (IT-HS), a new optimally resilient protocol for solving Byzantine Agreement in partial synchrony with information theoretic security guarantees. In particular, IT-HS does not depend on any PKI or common setup assumptions and is resilient to computationally unbounded adversaries. IT-HS is based on the Primary-Backup view-based paradigm. In IT-HS, in each view, and in each view change, each party sends only a constant number of words to every other party. This yields an O(n²) word and message complexity in each view. In addition, IT-HS requires just O(1) persistent local storage and O(n) transient local storage. Finally, like all Primary-Backup view-based protocols in partial synchrony, after the system becomes synchronous, all nonfaulty parties decide on a value in the first view a nonfaulty leader is chosen. Moreover, like PBFT and HotStuff, IT-HS is optimistically responsive: with a nonfaulty leader, parties decide as quickly as the network allows them to do so, without regard for the known upper bound on network delay. Our work improves in multiple dimensions upon the information theoretic version of PBFT presented by Miguel Castro, and can be seen as an information theoretic variant of the HotStuff paradigm.
Cite as

Ittai Abraham and Gilad Stern. Information Theoretic HotStuff. In 24th International Conference on Principles of Distributed Systems (OPODIS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 184, pp. 11:1-11:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{abraham_et_al:LIPIcs.OPODIS.2020.11,
  author =	{Abraham, Ittai and Stern, Gilad},
  title =	{{Information Theoretic HotStuff}},
  booktitle =	{24th International Conference on Principles of Distributed Systems (OPODIS 2020)},
  pages =	{11:1--11:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-176-4},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{184},
  editor =	{Bramas, Quentin and Oshman, Rotem and Romano, Paolo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2020.11},
  URN =		{urn:nbn:de:0030-drops-134969},
  doi =		{10.4230/LIPIcs.OPODIS.2020.11},
  annote =	{Keywords: byzantine agreement, partial synchrony, bounded space}
}
Document
DOI: 10.4230/LIPIcs.DISC.2020.25
Not a COINcidence: Sub-Quadratic Asynchronous Byzantine Agreement WHP

Authors: Shir Cohen, Idit Keidar, and Alexander Spiegelman

Published in: LIPIcs, Volume 179, 34th International Symposium on Distributed Computing (DISC 2020)

Abstract
King and Saia were the first to break the quadratic word complexity bound for Byzantine Agreement in synchronous systems against an adaptive adversary, and Algorand broke this bound with near-optimal resilience (first in the synchronous model and then with eventual-synchrony). Yet the question of asynchronous sub-quadratic Byzantine Agreement remained open. To the best of our knowledge, we are the first to answer this question in the affirmative. A key component of our solution is a shared coin algorithm based on a VRF. A second essential ingredient is VRF-based committee sampling, which we formalize and utilize in the asynchronous model for the first time. Our algorithms work against a delayed-adaptive adversary, which cannot perform after-the-fact removals but has full control of Byzantine processes and full information about communication in earlier rounds. Using committee sampling and our shared coin, we solve Byzantine Agreement with high probability, with a word complexity of Õ(n) and O(1) expected time, breaking the O(n²) bit barrier for asynchronous Byzantine Agreement.
Cite as

Shir Cohen, Idit Keidar, and Alexander Spiegelman. Not a COINcidence: Sub-Quadratic Asynchronous Byzantine Agreement WHP. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 25:1-25:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{cohen_et_al:LIPIcs.DISC.2020.25,
  author =	{Cohen, Shir and Keidar, Idit and Spiegelman, Alexander},
  title =	{{Not a COINcidence: Sub-Quadratic Asynchronous Byzantine Agreement WHP}},
  booktitle =	{34th International Symposium on Distributed Computing (DISC 2020)},
  pages =	{25:1--25:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-168-9},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{179},
  editor =	{Attiya, Hagit},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.25},
  URN =		{urn:nbn:de:0030-drops-131034},
  doi =		{10.4230/LIPIcs.DISC.2020.25},
  annote =	{Keywords: shared coin, Byzantine Agreement, VRF, sub-quadratic consensus protocol}
}
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