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Documents authored by Cohen, Shir

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Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2023.39
Brief Announcement: Subquadratic Multivalued Asynchronous Byzantine Agreement WHP

Authors: Shir Cohen and Idit Keidar

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

Abstract
There have been several reductions from multivalued consensus to binary consensus over the past 20 years. To the best of our knowledge, none of them solved it for Byzantine asynchronous settings. In this short paper, we close this gap. Moreover, we do so in subquadratic communication, using newly developed subquadratic binary Byzantine Agreement techniques.
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Shir Cohen and Idit Keidar. Brief Announcement: Subquadratic Multivalued Asynchronous Byzantine Agreement WHP. In 37th International Symposium on Distributed Computing (DISC 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 281, pp. 39:1-39:6, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{cohen_et_al:LIPIcs.DISC.2023.39,
  author =	{Cohen, Shir and Keidar, Idit},
  title =	{{Brief Announcement: Subquadratic Multivalued Asynchronous Byzantine Agreement WHP}},
  booktitle =	{37th International Symposium on Distributed Computing (DISC 2023)},
  pages =	{39:1--39:6},
  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.2023.39},
  URN =		{urn:nbn:de:0030-drops-191658},
  doi =		{10.4230/LIPIcs.DISC.2023.39},
  annote =	{Keywords: Byzantine agreement, subquadratic communication, fault tolerance in distributed systems}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2022.18
Make Every Word Count: Adaptive Byzantine Agreement with Fewer Words

Authors: Shir Cohen, Idit Keidar, and Alexander Spiegelman

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

Abstract
Byzantine Agreement (BA) is a key component in many distributed systems. While Dolev and Reischuk have proven a long time ago that quadratic communication complexity is necessary for worst-case runs, the question of what can be done in practically common runs with fewer failures remained open. In this paper we present the first Byzantine Broadcast algorithm with O(n(f+1)) communication complexity in a model with resilience of n = 2t+1, where 0 ≤ f ≤ t is the actual number of process failures in a run. And for BA with strong unanimity, we present the first optimal-resilience algorithm that has linear communication complexity in the failure-free case and a quadratic cost otherwise.
Cite as

Shir Cohen, Idit Keidar, and Alexander Spiegelman. Make Every Word Count: Adaptive Byzantine Agreement with Fewer Words. In 26th International Conference on Principles of Distributed Systems (OPODIS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 253, pp. 18:1-18:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{cohen_et_al:LIPIcs.OPODIS.2022.18,
  author =	{Cohen, Shir and Keidar, Idit and Spiegelman, Alexander},
  title =	{{Make Every Word Count: Adaptive Byzantine Agreement with Fewer Words}},
  booktitle =	{26th International Conference on Principles of Distributed Systems (OPODIS 2022)},
  pages =	{18:1--18:21},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2022.18},
  URN =		{urn:nbn:de:0030-drops-176385},
  doi =		{10.4230/LIPIcs.OPODIS.2022.18},
  annote =	{Keywords: Byzantine Agreement, Byzantine Broadcast, Adaptive communication}
}
Document
DOI: 10.4230/LIPIcs.DISC.2021.18
Tame the Wild with Byzantine Linearizability: Reliable Broadcast, Snapshots, and Asset Transfer

Authors: Shir Cohen and Idit Keidar

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

Abstract
We formalize Byzantine linearizability, a correctness condition that specifies whether a concurrent object with a sequential specification is resilient against Byzantine failures. Using this definition, we systematically study Byzantine-tolerant emulations of various objects from registers. We focus on three useful objects- reliable broadcast, atomic snapshot, and asset transfer. We prove that there exist n-process f-resilient Byzantine linearizable implementations of such objects from registers if and only if f < n/2.
Cite as

Shir Cohen and Idit Keidar. Tame the Wild with Byzantine Linearizability: Reliable Broadcast, Snapshots, and Asset Transfer. In 35th International Symposium on Distributed Computing (DISC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 209, pp. 18:1-18:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{cohen_et_al:LIPIcs.DISC.2021.18,
  author =	{Cohen, Shir and Keidar, Idit},
  title =	{{Tame the Wild with Byzantine Linearizability: Reliable Broadcast, Snapshots, and Asset Transfer}},
  booktitle =	{35th International Symposium on Distributed Computing (DISC 2021)},
  pages =	{18:1--18:18},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2021.18},
  URN =		{urn:nbn:de:0030-drops-148203},
  doi =		{10.4230/LIPIcs.DISC.2021.18},
  annote =	{Keywords: Byzantine linearizability, concurrent algorithms, snapshot, asset transfer}
}
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.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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