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Documents authored by Ghinea, Diana

Document
DOI: 10.4230/LIPIcs.DISC.2024.15
Convex Consensus with Asynchronous Fallback

Authors: Andrei Constantinescu, Diana Ghinea, Roger Wattenhofer, and Floris Westermann

Published in: LIPIcs, Volume 319, 38th International Symposium on Distributed Computing (DISC 2024)

Abstract
Convex Consensus (CC) allows a set of parties to agree on a value v inside the convex hull of their inputs with respect to a predefined abstract convexity notion, even in the presence of byzantine parties. In this work, we focus on achieving CC in the best-of-both-worlds paradigm, i.e., simultaneously tolerating at most t_s corruptions if communication is synchronous, and at most t_a ≤ t_s corruptions if it is asynchronous. Our protocol is randomized, which is a requirement under asynchrony, and we prove that it achieves optimal resilience. In the process, we introduce communication primitives tailored to the network-agnostic model. These are a deterministic primitive allowing parties to obtain intersecting views (Gather), and a randomized primitive leading to identical views (Agreement on a Core-Set). Our primitives provide stronger guarantees than previous counterparts, making them of independent interest.
Cite as

Andrei Constantinescu, Diana Ghinea, Roger Wattenhofer, and Floris Westermann. Convex Consensus with Asynchronous Fallback. In 38th International Symposium on Distributed Computing (DISC 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 319, pp. 15:1-15:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{constantinescu_et_al:LIPIcs.DISC.2024.15,
  author =	{Constantinescu, Andrei and Ghinea, Diana and Wattenhofer, Roger and Westermann, Floris},
  title =	{{Convex Consensus with Asynchronous Fallback}},
  booktitle =	{38th International Symposium on Distributed Computing (DISC 2024)},
  pages =	{15:1--15:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-352-2},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{319},
  editor =	{Alistarh, Dan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2024.15},
  URN =		{urn:nbn:de:0030-drops-212411},
  doi =		{10.4230/LIPIcs.DISC.2024.15},
  annote =	{Keywords: convex consensus, network-agnostic protocols, agreement on a core-set}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2024.43
Brief Announcement: Unifying Partial Synchrony

Authors: Andrei Constantinescu, Diana Ghinea, Jakub Sliwinski, and Roger Wattenhofer

Published in: LIPIcs, Volume 319, 38th International Symposium on Distributed Computing (DISC 2024)

Abstract
The distributed computing literature considers multiple options for modeling communication. Most simply, communication is categorized as either synchronous or asynchronous. Synchronous communication assumes that messages get delivered within a publicly known timeframe and that parties' clocks are synchronized. Asynchronous communication, on the other hand, only assumes that messages get delivered eventually. A more nuanced approach, or a middle ground between the two extremes, is given by the partially synchronous model, which is arguably the most realistic option. This model comes in two commonly considered flavors: ii) The Global Stabilization Time (GST) model: after an (unknown) amount of time, the network becomes synchronous. This captures scenarios where network issues are transient. iii) The Unknown Latency (UL) model: the network is, in fact, synchronous, but the message delay bound is unknown. This work formally establishes that any time-agnostic property that can be achieved by a protocol in the UL model can also be achieved by a (possibly different) protocol in the GST model. By time-agnostic, we mean properties that can depend on the order in which events happen but not on time as measured by the parties. Most properties considered in distributed computing are time-agnostic. The converse was already known, even without the time-agnostic requirement, so our result shows that the two network conditions are, under one sensible assumption, equally demanding.
Cite as

Andrei Constantinescu, Diana Ghinea, Jakub Sliwinski, and Roger Wattenhofer. Brief Announcement: Unifying Partial Synchrony. In 38th International Symposium on Distributed Computing (DISC 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 319, pp. 43:1-43:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{constantinescu_et_al:LIPIcs.DISC.2024.43,
  author =	{Constantinescu, Andrei and Ghinea, Diana and Sliwinski, Jakub and Wattenhofer, Roger},
  title =	{{Brief Announcement: Unifying Partial Synchrony}},
  booktitle =	{38th International Symposium on Distributed Computing (DISC 2024)},
  pages =	{43:1--43:7},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-352-2},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{319},
  editor =	{Alistarh, Dan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2024.43},
  URN =		{urn:nbn:de:0030-drops-212717},
  doi =		{10.4230/LIPIcs.DISC.2024.43},
  annote =	{Keywords: partial synchrony, unknown latency, global stabilization time}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2023.8
A Fair and Resilient Decentralized Clock Network for Transaction Ordering

Authors: Andrei Constantinescu, Diana Ghinea, Lioba Heimbach, Zilin Wang, and Roger Wattenhofer

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

Abstract
Traditional blockchain design gives miners or validators full control over transaction ordering, i.e., they can freely choose which transactions to include or exclude, as well as in which order. While not an issue initially, the emergence of decentralized finance has introduced new transaction order dependencies allowing parties in control of the ordering to make a profit by front-running others' transactions. In this work, we present the Decentralized Clock Network, a new approach for achieving fair transaction ordering. Users submit their transactions to the network’s clocks, which run an agreement protocol that provides each transaction with a timestamp of receipt which is then used to define the transactions' order. By separating agreement from ordering, our protocol is efficient and has a simpler design compared to other available solutions. Moreover, our protocol brings to the blockchain world the paradigm of asynchronous fallback, where the algorithm operates with stronger fairness guarantees during periods of synchronous use, switching to an asynchronous mode only during times of increased network delay.
Cite as

Andrei Constantinescu, Diana Ghinea, Lioba Heimbach, Zilin Wang, and Roger Wattenhofer. A Fair and Resilient Decentralized Clock Network for Transaction Ordering. In 27th International Conference on Principles of Distributed Systems (OPODIS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 286, pp. 8:1-8:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{constantinescu_et_al:LIPIcs.OPODIS.2023.8,
  author =	{Constantinescu, Andrei and Ghinea, Diana and Heimbach, Lioba and Wang, Zilin and Wattenhofer, Roger},
  title =	{{A Fair and Resilient Decentralized Clock Network for Transaction Ordering}},
  booktitle =	{27th International Conference on Principles of Distributed Systems (OPODIS 2023)},
  pages =	{8:1--8:20},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2023.8},
  URN =		{urn:nbn:de:0030-drops-194989},
  doi =		{10.4230/LIPIcs.OPODIS.2023.8},
  annote =	{Keywords: Median Validity, Blockchain, Fair Ordering, Front-running Prevention, Miner Extractable Value}
}
Document
DOI: 10.4230/LIPIcs.DISC.2020.29
From Partial to Global Asynchronous Reliable Broadcast

Authors: Diana Ghinea, Martin Hirt, and Chen-Da Liu-Zhang

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

Abstract
Broadcast is a fundamental primitive in distributed computing. It allows a sender to consistently distribute a message among n recipients. The seminal result of Pease et al. [JACM'80] shows that in a complete network of synchronous bilateral channels, broadcast is achievable if and only if the number of corruptions is bounded by t < n/3. To overcome this bound, a fascinating line of works, Fitzi and Maurer [STOC'00], Considine et al. [JC'05], and Raykov [ICALP'15], proposed strengthening the communication network by assuming partial synchronous broadcast channels, which guarantee consistency among a subset of recipients. We extend this line of research to the asynchronous setting. We consider reliable broadcast protocols assuming a communication network which provides each subset of b parties with reliable broadcast channels. A natural question is to investigate the trade-off between the size b and the corruption threshold t. We answer this question by showing feasibility and impossibility results: - A reliable broadcast protocol Π_{RBC} that: - For 3 ≤ b ≤ 4, is secure up to t < n/2 corruptions. - For b > 4 even, is secure up to t < ((b-4)/(b-2) n + 8/(b-2)) corruptions. - For b > 4 odd, is secure up to t < ((b-3)/(b-1) n + 6/(b-1)) corruptions. - A nonstop reliable broadcast Π_{nRBC}, where parties are guaranteed to obtain output as in reliable broadcast but may need to run forever, secure up to t < (b-1)/(b+1) n corruptions. - There is no protocol for (nonstop) reliable broadcast secure up to t ≥ (b-1)/(b+1) n corruptions, implying that Π_{RBC} is an asymptotically optimal reliable broadcast protocol, and Π_{nRBC} is an optimal nonstop reliable broadcast protocol.
Cite as

Diana Ghinea, Martin Hirt, and Chen-Da Liu-Zhang. From Partial to Global Asynchronous Reliable Broadcast. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 29:1-29:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{ghinea_et_al:LIPIcs.DISC.2020.29,
  author =	{Ghinea, Diana and Hirt, Martin and Liu-Zhang, Chen-Da},
  title =	{{From Partial to Global Asynchronous Reliable Broadcast}},
  booktitle =	{34th International Symposium on Distributed Computing (DISC 2020)},
  pages =	{29:1--29:16},
  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.2020.29},
  URN =		{urn:nbn:de:0030-drops-131074},
  doi =		{10.4230/LIPIcs.DISC.2020.29},
  annote =	{Keywords: asynchronous broadcast, partial broadcast}
}
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