19 Search Results for "Malkhi, Dahlia"

Document
DOI: 10.4230/LIPIcs.ESA.2024.66
Shortest Path Separators in Unit Disk Graphs

Authors: Elfarouk Harb, Zhengcheng Huang, and Da Wei Zheng

Published in: LIPIcs, Volume 308, 32nd Annual European Symposium on Algorithms (ESA 2024)

Abstract
We introduce a new balanced separator theorem for unit-disk graphs involving two shortest paths combined with the 1-hop neighbours of those paths and two other vertices. This answers an open problem of Yan, Xiang and Dragan [CGTA '12] and improves their result that requires removing the 3-hop neighbourhood of two shortest paths. Our proof uses very different ideas, including Delaunay triangulations and a generalization of the celebrated balanced separator theorem of Lipton and Tarjan [J. Appl. Math. '79] to systems of non-intersecting paths.
Cite as

Elfarouk Harb, Zhengcheng Huang, and Da Wei Zheng. Shortest Path Separators in Unit Disk Graphs. In 32nd Annual European Symposium on Algorithms (ESA 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 308, pp. 66:1-66:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{harb_et_al:LIPIcs.ESA.2024.66,
  author =	{Harb, Elfarouk and Huang, Zhengcheng and Zheng, Da Wei},
  title =	{{Shortest Path Separators in Unit Disk Graphs}},
  booktitle =	{32nd Annual European Symposium on Algorithms (ESA 2024)},
  pages =	{66:1--66:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-338-6},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{308},
  editor =	{Chan, Timothy and Fischer, Johannes and Iacono, John and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2024.66},
  URN =		{urn:nbn:de:0030-drops-211375},
  doi =		{10.4230/LIPIcs.ESA.2024.66},
  annote =	{Keywords: Balanced shortest path separators, unit disk graphs, crossings}
}
Document
DOI: 10.4230/LIPIcs.ESA.2024.71
Towards Communication-Efficient Peer-To-Peer Networks

Authors: Khalid Hourani, William K. Moses Jr., and Gopal Pandurangan

Published in: LIPIcs, Volume 308, 32nd Annual European Symposium on Algorithms (ESA 2024)

Abstract
We focus on designing Peer-to-Peer (P2P) networks that enable efficient communication. Over the last two decades, there has been substantial algorithmic research on distributed protocols for building P2P networks with various desirable properties such as high expansion, low diameter, and robustness to a large number of deletions. A key underlying theme in all of these works is to distributively build a random graph topology that guarantees the above properties. Moreover, the random connectivity topology is widely deployed in many P2P systems today, including those that implement blockchains and cryptocurrencies. However, a major drawback of using a random graph topology for a P2P network is that the random topology does not respect the underlying (Internet) communication topology. This creates a large propagation delay, which is a major communication bottleneck in modern P2P networks. In this paper, we work towards designing P2P networks that are communication-efficient (having small propagation delay) with provable guarantees. Our main contribution is an efficient, decentralized protocol, Close-Weaver, that transforms a random graph topology embedded in an underlying Euclidean space into a topology that also respects the underlying metric. We then present efficient point-to-point routing and broadcast protocols that achieve essentially optimal performance with respect to the underlying space.
Cite as

Khalid Hourani, William K. Moses Jr., and Gopal Pandurangan. Towards Communication-Efficient Peer-To-Peer Networks. In 32nd Annual European Symposium on Algorithms (ESA 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 308, pp. 71:1-71:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{hourani_et_al:LIPIcs.ESA.2024.71,
  author =	{Hourani, Khalid and Moses Jr., William K. and Pandurangan, Gopal},
  title =	{{Towards Communication-Efficient Peer-To-Peer Networks}},
  booktitle =	{32nd Annual European Symposium on Algorithms (ESA 2024)},
  pages =	{71:1--71:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-338-6},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{308},
  editor =	{Chan, Timothy and Fischer, Johannes and Iacono, John and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2024.71},
  URN =		{urn:nbn:de:0030-drops-211428},
  doi =		{10.4230/LIPIcs.ESA.2024.71},
  annote =	{Keywords: Peer-to-Peer Networks, Overlay Construction Protocol, Expanders, Broadcast, Geometric Routing}
}
Document
DOI: 10.4230/LIPIcs.AFT.2024.29
Transaction Fee Mechanism Design in a Post-MEV World

Authors: Maryam Bahrani, Pranav Garimidi, and Tim Roughgarden

Published in: LIPIcs, Volume 316, 6th Conference on Advances in Financial Technologies (AFT 2024)

Abstract
The incentive-compatibility properties of blockchain transaction fee mechanisms have been investigated with passive block producers that are motivated purely by the net rewards earned at the consensus layer. This paper introduces a model of active block producers that have their own private valuations for blocks (representing, for example, additional value derived from the application layer). The block producer surplus in our model can be interpreted as one of the more common colloquial meanings of the phrase "maximal extractable value (MEV)." We first prove that transaction fee mechanism design is fundamentally more difficult with active block producers than with passive ones: With active block producers, no non-trivial or approximately welfare-maximizing transaction fee mechanism can be incentive-compatible for both users and block producers. These results can be interpreted as a mathematical justification for augmenting transaction fee mechanisms with additional components such as order flow auctions, block producer competition, trusted hardware, or cryptographic techniques. We then consider a more fine-grained model of block production that more accurately reflects current practice, in which we distinguish the roles of "searchers" (who actively identify opportunities for value extraction from the application layer and compete for the right to take advantage of them) and "proposers" (who participate directly in the blockchain protocol and make the final choice of the published block). Searchers can effectively act as an "MEV oracle" for a transaction fee mechanism, thereby enlarging the design space. Here, we first consider a TFM that is inspired by how searchers have traditionally been incorporated into the block production process, with each transaction effectively sold off to a searcher through a first-price auction. We then explore the TFM design space with searchers more generally, and design a mechanism that circumvents our impossibility results for TFMs without searchers. Our mechanism (the "SAKA" mechanism) is incentive-compatible (for users, searchers, and the block producer), sybil-proof, and guarantees roughly 50% of the maximum-possible welfare when transaction sizes are small relative to block sizes. We conclude with a matching negative result: even when transaction sizes are small, no DSIC and sybil-proof deterministic TFM can guarantee more than 50% of the maximum-possible welfare.
Cite as

Maryam Bahrani, Pranav Garimidi, and Tim Roughgarden. Transaction Fee Mechanism Design in a Post-MEV World. In 6th Conference on Advances in Financial Technologies (AFT 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 316, pp. 29:1-29:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{bahrani_et_al:LIPIcs.AFT.2024.29,
  author =	{Bahrani, Maryam and Garimidi, Pranav and Roughgarden, Tim},
  title =	{{Transaction Fee Mechanism Design in a Post-MEV World}},
  booktitle =	{6th Conference on Advances in Financial Technologies (AFT 2024)},
  pages =	{29:1--29:24},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-345-4},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{316},
  editor =	{B\"{o}hme, Rainer and Kiffer, Lucianna},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2024.29},
  URN =		{urn:nbn:de:0030-drops-209658},
  doi =		{10.4230/LIPIcs.AFT.2024.29},
  annote =	{Keywords: MEV, Transaction Fee Mechanisms, Auctions}
}
Document
DOI: 10.4230/LIPIcs.AFT.2024.3
CFT-Forensics: High-Performance Byzantine Accountability for Crash Fault Tolerant Protocols

Authors: Weizhao Tang, Peiyao Sheng, Ronghao Ni, Pronoy Roy, Xuechao Wang, Giulia Fanti, and Pramod Viswanath

Published in: LIPIcs, Volume 316, 6th Conference on Advances in Financial Technologies (AFT 2024)

Abstract
Crash fault tolerant (CFT) consensus algorithms are commonly used in scenarios where system components are trusted - e.g., enterprise settings and government infrastructure. However, CFT consensus can be broken by even a single corrupt node. A desirable property in the face of such potential Byzantine faults is accountability: if a corrupt node breaks the protocol and affects consensus safety, it should be possible to identify the culpable components with cryptographic integrity from the node states. Today, the best-known protocol for providing accountability to CFT protocols is called PeerReview; it essentially records a signed transcript of all messages sent during the CFT protocol. Because PeerReview is agnostic to the underlying CFT protocol, it incurs high communication and storage overhead. We propose CFT-Forensics, an accountability framework for CFT protocols. We show that for a special family of forensics-compliant CFT protocols (which includes widely-used CFT protocols like Raft and multi-Paxos), CFT-Forensics gives provable accountability guarantees. Under realistic deployment settings, we show theoretically that CFT-Forensics operates at a fraction of the cost of PeerReview. We subsequently instantiate CFT-Forensics for Raft, and implement Raft-Forensics as an extension to the popular nuRaft library. In extensive experiments, we demonstrate that Raft-Forensics adds low overhead to vanilla Raft. With 256 byte messages, Raft-Forensics achieves a peak throughput 87.8% of vanilla Raft at 46% higher latency (+44 ms). We finally integrate Raft-Forensics into the open-source central bank digital currency OpenCBDC, and show that in wide-area network experiments, Raft-Forensics achieves 97.8% of the throughput of Raft, with 14.5% higher latency (+326 ms).
Cite as

Weizhao Tang, Peiyao Sheng, Ronghao Ni, Pronoy Roy, Xuechao Wang, Giulia Fanti, and Pramod Viswanath. CFT-Forensics: High-Performance Byzantine Accountability for Crash Fault Tolerant Protocols. In 6th Conference on Advances in Financial Technologies (AFT 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 316, pp. 3:1-3:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{tang_et_al:LIPIcs.AFT.2024.3,
  author =	{Tang, Weizhao and Sheng, Peiyao and Ni, Ronghao and Roy, Pronoy and Wang, Xuechao and Fanti, Giulia and Viswanath, Pramod},
  title =	{{CFT-Forensics: High-Performance Byzantine Accountability for Crash Fault Tolerant Protocols}},
  booktitle =	{6th Conference on Advances in Financial Technologies (AFT 2024)},
  pages =	{3:1--3:25},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-345-4},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{316},
  editor =	{B\"{o}hme, Rainer and Kiffer, Lucianna},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2024.3},
  URN =		{urn:nbn:de:0030-drops-209399},
  doi =		{10.4230/LIPIcs.AFT.2024.3},
  annote =	{Keywords: CFT Protocols, forensics, blockchain}
}
Document
DOI: 10.4230/LIPIcs.AFT.2024.8
A Circuit Approach to Constructing Blockchains on Blockchains

Authors: Ertem Nusret Tas, David Tse, and Yifei Wang

Published in: LIPIcs, Volume 316, 6th Conference on Advances in Financial Technologies (AFT 2024)

Abstract
Recent years have witnessed an explosion of blockchains, each with an open ledger that anyone can read from and write to. In this multi-chain world, an important question emerges: how can we build a more secure overlay blockchain by reading from and writing to a given set of blockchains? Drawing an analogy with switching circuits, we approach the problem by defining two basic compositional operations between blockchains, serial and triangular compositions, and use these operations as building blocks to construct general overlay blockchains. Under the partially synchronous setting, we have the following results: 1) the serial composition, between two certificate-producing blockchains, yields an overlay blockchain that is safe if at least one of the two underlay blockchains is safe and that is live if both of them are live; 2) the triangular composition between three blockchains, akin to parallel composition of switching circuits, yields an overlay blockchain that is safe if all underlay blockchains are safe and that is live if over half of them are live; 3) repeated composition of these two basic operations can yield all possible tradeoffs of safety and liveness for an overlay blockchain built on an arbitrary number of underlay chains. The results are also extended to the synchronous setting.
Cite as

Ertem Nusret Tas, David Tse, and Yifei Wang. A Circuit Approach to Constructing Blockchains on Blockchains. In 6th Conference on Advances in Financial Technologies (AFT 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 316, pp. 8:1-8:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{tas_et_al:LIPIcs.AFT.2024.8,
  author =	{Tas, Ertem Nusret and Tse, David and Wang, Yifei},
  title =	{{A Circuit Approach to Constructing Blockchains on Blockchains}},
  booktitle =	{6th Conference on Advances in Financial Technologies (AFT 2024)},
  pages =	{8:1--8:25},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-345-4},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{316},
  editor =	{B\"{o}hme, Rainer and Kiffer, Lucianna},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2024.8},
  URN =		{urn:nbn:de:0030-drops-209442},
  doi =		{10.4230/LIPIcs.AFT.2024.8},
  annote =	{Keywords: interchain consensus protocols, serial composition, triangular composition, circuits}
}
Document
DOI: 10.4230/OASIcs.Tokenomics.2022.6
Maximal Extractable Value (MEV) Protection on a DAG

Authors: Dahlia Malkhi and Pawel Szalachowski

Published in: OASIcs, Volume 110, 4th International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2022)

Abstract
Many cryptocurrency platforms are vulnerable to Maximal Extractable Value (MEV) attacks [Daian et al., 2020], where a malicious consensus leader can inject transactions or change the order of user transactions to maximize its profit. A promising line of research in MEV mitigation is to enhance the Byzantine fault tolerance (BFT) consensus core of blockchains by new functionalities, like hiding transaction contents, such that malicious parties cannot analyze and exploit them until they are ordered. An orthogonal line of research demonstrates excellent performance for BFT protocols designed around Directed Acyclic Graphs (DAG). They provide high throughput by keeping high network utilization, decoupling transactions' dissemination from their metadata ordering, and encoding consensus logic efficiently over a DAG representing a causal ordering of disseminated messages. This paper explains how to combine these two advances. It introduces a DAG-based protocol called Fino, that integrates MEV-resistance features into DAG-based BFT without delaying the steady spreading of transactions by the DAG transport and with zero message overhead. The scheme operates without complex secret share verifiability or recoverability, and avoids costly threshold encryption.
Cite as

Dahlia Malkhi and Pawel Szalachowski. Maximal Extractable Value (MEV) Protection on a DAG. In 4th International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2022). Open Access Series in Informatics (OASIcs), Volume 110, pp. 6:1-6:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{malkhi_et_al:OASIcs.Tokenomics.2022.6,
  author =	{Malkhi, Dahlia and Szalachowski, Pawel},
  title =	{{Maximal Extractable Value (MEV) Protection on a DAG}},
  booktitle =	{4th International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2022)},
  pages =	{6:1--6:17},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-274-7},
  ISSN =	{2190-6807},
  year =	{2023},
  volume =	{110},
  editor =	{Amoussou-Guenou, Yackolley and Kiayias, Aggelos and Verdier, Marianne},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.Tokenomics.2022.6},
  URN =		{urn:nbn:de:0030-drops-184231},
  doi =		{10.4230/OASIcs.Tokenomics.2022.6},
  annote =	{Keywords: DAG, MEV, consensus, BFT}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2021.7
Twins: BFT Systems Made Robust

Authors: Shehar Bano, Alberto Sonnino, Andrey Chursin, Dmitri Perelman, Zekun Li, Avery Ching, and Dahlia Malkhi

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

Abstract
This paper presents Twins, an automated unit test generator of Byzantine attacks. Twins implements three types of Byzantine behaviors: (i) leader equivocation, (ii) double voting, and (iii) losing internal state such as forgetting "locks" guarding voted values. To emulate interesting attacks by a Byzantine node, it instantiates twin copies of the node instead of one, giving both twins the same identities and network credentials. To the rest of the system, the twins appear indistinguishable from a single node behaving in a "questionable" manner. Twins can systematically generate Byzantine attack scenarios at scale, execute them in a controlled manner, and examine their behavior. Twins scenarios iterate over protocol rounds and vary the communication patterns among nodes. Twins runs in a production setting within DiemBFT where it can execute 44M Twins-generated scenarios daily. Whereas the system at hand did not manifest errors, subtle safety bugs that were deliberately injected for the purpose of validating the implementation of Twins itself were exposed within minutes. Twins can prevent developers from regressing correctness when updating the codebase, introducing new features, or performing routine maintenance tasks. Twins only requires a thin wrapper over DiemBFT, we thus envision other systems using it. Building on this idea, one new attack and several known attacks against other BFT protocols were materialized as Twins scenarios. In all cases, the target protocols break within fewer than a dozen protocol rounds, hence it is realistic for the Twins approach to expose the problems.
Cite as

Shehar Bano, Alberto Sonnino, Andrey Chursin, Dmitri Perelman, Zekun Li, Avery Ching, and Dahlia Malkhi. Twins: BFT Systems Made Robust. In 25th International Conference on Principles of Distributed Systems (OPODIS 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 217, pp. 7:1-7:29, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{bano_et_al:LIPIcs.OPODIS.2021.7,
  author =	{Bano, Shehar and Sonnino, Alberto and Chursin, Andrey and Perelman, Dmitri and Li, Zekun and Ching, Avery and Malkhi, Dahlia},
  title =	{{Twins: BFT Systems Made Robust}},
  booktitle =	{25th International Conference on Principles of Distributed Systems (OPODIS 2021)},
  pages =	{7:1--7:29},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2021.7},
  URN =		{urn:nbn:de:0030-drops-157825},
  doi =		{10.4230/LIPIcs.OPODIS.2021.7},
  annote =	{Keywords: Distributed Systems, Byzantine Fault Tolerance, Real-World Deployment}
}
Document
Invited Talk
DOI: 10.4230/LIPIcs.DISC.2021.2
Tech Transfer Stories and Takeaways (Invited Talk)

Authors: Dahlia Malkhi

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

Abstract
In this talk, I will share impressions from several industrial research project experiences that reached production and became part of successful products. I will go through four stories of how these systems transpired and their journey to impact. All of the stories are in the distributed computing arena, and more specifically, they revolve around the state-machine-replication paradigm. Yet, I hope that the take-aways from the experience of building foundations for these systems may be of interest and value to everyone, no matter the discipline.
Cite as

Dahlia Malkhi. Tech Transfer Stories and Takeaways (Invited Talk). In 35th International Symposium on Distributed Computing (DISC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 209, p. 2:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{malkhi:LIPIcs.DISC.2021.2,
  author =	{Malkhi, Dahlia},
  title =	{{Tech Transfer Stories and Takeaways}},
  booktitle =	{35th International Symposium on Distributed Computing (DISC 2021)},
  pages =	{2:1--2:1},
  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.2021.2},
  URN =		{urn:nbn:de:0030-drops-148045},
  doi =		{10.4230/LIPIcs.DISC.2021.2},
  annote =	{Keywords: Tech Transfer, Distributed Systems}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2021.46
Brief Announcement: Twins – BFT Systems Made Robust

Authors: Shehar Bano, Alberto Sonnino, Andrey Chursin, Dmitri Perelman, Zekun Li, Avery Ching, and Dahlia Malkhi

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

Abstract
Twins is an effective strategy for generating test scenarios with Byzantine [Lamport et al., 1982] nodes in order to find flaws in Byzantine Fault Tolerant (BFT) systems. Twins finds flaws in the design or implementation of BFT protocols that may cause correctness issues. The main idea of Twins is the following: running twin instances of a node that use correct, unmodified code and share the same network identity and credentials allows to emulate most interesting Byzantine behaviors. Because a twin executes normal, unmodified node code, building Twins only requires a thin wrapper over an existing distributed system designed for Byzantine tolerance. To emulate material, interesting scenarios with Byzantine nodes, it instantiates one or more twin copies of the node, giving the twins the same identities and network credentials as the original node. To the rest of the system, the node and all its twins appear indistinguishable from a single node behaving in a "questionable" manner. This approach generates many interesting Byzantine behaviors, including equivocation, double voting, and losing internal state, while forgoing uninteresting behavior scenarios that can be filtered at the transport layer, such as producing semantically invalid messages. Building on configurations with twin nodes, Twins systematically generates scenarios with Byzantine nodes via enumeration over protocol rounds and communication patterns among nodes. Despite this being inherently exponential, one new flaw and several known flaws were materialized by Twins in the arena of BFT consensus protocols. In all cases, protocols break within fewer than a dozen protocol rounds, hence it is realistic for the Twins approach to expose the problems. In two of these cases, it took the community more than a decade to discover protocol flaws that Twins would have surfaced within minutes. Additionally, Twins has been incorporated into the continuous release testing process of a production setting (DiemBFT) in which it can execute 44M Twins-generated scenarios daily.
Cite as

Shehar Bano, Alberto Sonnino, Andrey Chursin, Dmitri Perelman, Zekun Li, Avery Ching, and Dahlia Malkhi. Brief Announcement: Twins – BFT Systems Made Robust. In 35th International Symposium on Distributed Computing (DISC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 209, pp. 46:1-46:4, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{bano_et_al:LIPIcs.DISC.2021.46,
  author =	{Bano, Shehar and Sonnino, Alberto and Chursin, Andrey and Perelman, Dmitri and Li, Zekun and Ching, Avery and Malkhi, Dahlia},
  title =	{{Brief Announcement: Twins – BFT Systems Made Robust}},
  booktitle =	{35th International Symposium on Distributed Computing (DISC 2021)},
  pages =	{46:1--46:4},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2021.46},
  URN =		{urn:nbn:de:0030-drops-148485},
  doi =		{10.4230/LIPIcs.DISC.2021.46},
  annote =	{Keywords: Distributed Systems, Byzantine Fault Tolerance, Real-World Deployment}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2020.9
ACE: Abstract Consensus Encapsulation for Liveness Boosting of State Machine Replication

Authors: Alexander Spiegelman, Arik Rinberg, and Dahlia Malkhi

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

Abstract
With the emergence of attack-prone cross-organization systems, providing asynchronous state machine replication (SMR) solutions is no longer a theoretical concern. This paper presents ACE, a framework for the design of such fault tolerant systems. Leveraging a known paradigm for randomized consensus solutions, ACE wraps existing practical solutions and real-life systems, boosting their liveness under adversarial conditions and, at the same time, promoting load balancing and fairness. Boosting is achieved without modifying the overall design or the engineering of these solutions. ACE is aimed at boosting the prevailing approach for practical fault tolerance. This approach, often named partial synchrony, is based on a leader-based paradigm: a good leader makes progress and a bad leader does no harm. The partial synchrony approach focuses on safety and forgoes liveness under targeted and dynamic attacks. Specifically, an attacker might block specific leaders, e.g., through a denial of service, to prevent progress. ACE provides boosting by running waves of parallel leaders and selecting a winning leader only retroactively, achieving boosting at a linear communication cost increase. ACE is agnostic to the fault model, inheriting it s failure model from the wrapped solution assumptions. As our evaluation shows, an asynchronous Byzantine fault tolerance (BFT) replication system built with ACE around an existing partially synchronous BFT protocol demonstrates reasonable slow-down compared with the base BFT protocol during faultless synchronous scenarios, yet exhibits significant speedup while the system is under attack.
Cite as

Alexander Spiegelman, Arik Rinberg, and Dahlia Malkhi. ACE: Abstract Consensus Encapsulation for Liveness Boosting of State Machine Replication. In 24th International Conference on Principles of Distributed Systems (OPODIS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 184, pp. 9:1-9:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{spiegelman_et_al:LIPIcs.OPODIS.2020.9,
  author =	{Spiegelman, Alexander and Rinberg, Arik and Malkhi, Dahlia},
  title =	{{ACE: Abstract Consensus Encapsulation for Liveness Boosting of State Machine Replication}},
  booktitle =	{24th International Conference on Principles of Distributed Systems (OPODIS 2020)},
  pages =	{9:1--9:18},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2020.9},
  URN =		{urn:nbn:de:0030-drops-134948},
  doi =		{10.4230/LIPIcs.OPODIS.2020.9},
  annote =	{Keywords: Framework, Asynchronous, Consensus boosting, State Machine Replication}
}
Document
DOI: 10.4230/LIPIcs.DISC.2020.23
Making Byzantine Consensus Live

Authors: Manuel Bravo, Gregory Chockler, and Alexey Gotsman

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

Abstract
Partially synchronous Byzantine consensus protocols typically structure their execution into a sequence of views, each with a designated leader process. The key to guaranteeing liveness in these protocols is to ensure that all correct processes eventually overlap in a view with a correct leader for long enough to reach a decision. We propose a simple view synchronizer abstraction that encapsulates the corresponding functionality for Byzantine consensus protocols, thus simplifying their design. We present a formal specification of a view synchronizer and its implementation under partial synchrony, which runs in bounded space despite tolerating message loss during asynchronous periods. We show that our synchronizer specification is strong enough to guarantee liveness for single-shot versions of several well-known Byzantine consensus protocols, including HotStuff, Tendermint, PBFT and SBFT. We furthermore give precise latency bounds for these protocols when using our synchronizer. By factoring out the functionality of view synchronization we are able to specify and analyze the protocols in a uniform framework, which allows comparing them and highlights trade-offs.
Cite as

Manuel Bravo, Gregory Chockler, and Alexey Gotsman. Making Byzantine Consensus Live. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 23:1-23:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{bravo_et_al:LIPIcs.DISC.2020.23,
  author =	{Bravo, Manuel and Chockler, Gregory and Gotsman, Alexey},
  title =	{{Making Byzantine Consensus Live}},
  booktitle =	{34th International Symposium on Distributed Computing (DISC 2020)},
  pages =	{23:1--23:17},
  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.2020.23},
  URN =		{urn:nbn:de:0030-drops-131013},
  doi =		{10.4230/LIPIcs.DISC.2020.23},
  annote =	{Keywords: Byzantine consensus, blockchain, partial synchrony, liveness}
}
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}
}
Document
Keynote Lecture
DOI: 10.4230/OASIcs.Tokenomics.2019.2
Flexible BFT: Separating BFT Protocol Design from the Fault Model (Keynote Lecture)

Authors: Dahlia Malkhi

Published in: OASIcs, Volume 71, International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2019)

Abstract
Byzantine Fault Tolerant (BFT) protocols designed for building replicated services collapse if deployed under settings that differ from the fault model they are designed for. For example, in a partial-synchrony model, a known lower bound for BFT is 1/3. Optimal-resilience solutions completely break if the fraction of Byzantine faults exceeds 1/3. The only way we know to achieve > 1/3 resilience is by assuming synchrony, but this requires the protocol to be designed with that assumption. Flexible BFT is a new approach to BFT protocol design that separates between the fault model and the solution. Clients in Flexible BFT specify (i) the adversarial threshold they need to tolerate, and (ii) whether they believe in synchrony (and the presumed bound on transmission delays). We present a Flexible BFT solution that simultaneously supports different clients, who differ simply by the number of messages and/or time the clients are willing to wait for. At an even finer grain, Flexible BFT supports under the same solution high-value and low-value transactions, each tolerating a different threat model.
Cite as

Dahlia Malkhi. Flexible BFT: Separating BFT Protocol Design from the Fault Model (Keynote Lecture). In International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2019). Open Access Series in Informatics (OASIcs), Volume 71, p. 2:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{malkhi:OASIcs.Tokenomics.2019.2,
  author =	{Malkhi, Dahlia},
  title =	{{Flexible BFT: Separating BFT Protocol Design from the Fault Model}},
  booktitle =	{International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2019)},
  pages =	{2:1--2:1},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-108-5},
  ISSN =	{2190-6807},
  year =	{2020},
  volume =	{71},
  editor =	{Danos, Vincent and Herlihy, Maurice and Potop-Butucaru, Maria and Prat, Julien and Tucci-Piergiovanni, Sara},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.Tokenomics.2019.2},
  URN =		{urn:nbn:de:0030-drops-119660},
  doi =		{10.4230/OASIcs.Tokenomics.2019.2},
  annote =	{Keywords: Byzantine fault-tolerance, blockchains}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2019.4
FairLedger: A Fair Blockchain Protocol for Financial Institutions

Authors: Kfir Lev-Ari, Alexander Spiegelman, Idit Keidar, and Dahlia Malkhi

Published in: LIPIcs, Volume 153, 23rd International Conference on Principles of Distributed Systems (OPODIS 2019)

Abstract
Financial institutions nowadays are looking into technologies for permissioned blockchains. A major effort in this direction is Hyperledger, an open source project hosted by the Linux Foundation and backed by a consortium of over a hundred companies. A key component in permissioned blockchain protocols is a byzantine fault tolerant (BFT) consensus engine that orders transactions. However, currently available BFT solutions in Hyperledger (as well as in the literature at large) are inadequate for financial settings; they are not designed to ensure fairness or to tolerate the selfish behavior that inevitably arises when financial institutions strive to maximize their own profit. We present FairLedger, a permissioned BFT blockchain protocol, which is fair, deigned to deal with rational behavior, and, no less important, easy to understand and implement. Our secret sauce is a new communication abstraction called detectable all-to-all (DA2A), which allows us to detect players (byzantine or rational) that deviate from the protocol and punish them. We implement FairLedger in the Hyperledger open source project using the Iroha framework - one of the biggest projects therein. To evaluate FairLegder’s performance, we also implement it in the PBFT framework and compare the two protocols. Our results show that in failure-free scenarios in wide-area settings, FairLedger achieves better throughput than both Iroha’s implementation and PBFT.
Cite as

Kfir Lev-Ari, Alexander Spiegelman, Idit Keidar, and Dahlia Malkhi. FairLedger: A Fair Blockchain Protocol for Financial Institutions. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 4:1-4:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{levari_et_al:LIPIcs.OPODIS.2019.4,
  author =	{Lev-Ari, Kfir and Spiegelman, Alexander and Keidar, Idit and Malkhi, Dahlia},
  title =	{{FairLedger: A Fair Blockchain Protocol for Financial Institutions}},
  booktitle =	{23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
  pages =	{4:1--4:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-133-7},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{153},
  editor =	{Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.4},
  URN =		{urn:nbn:de:0030-drops-117904},
  doi =		{10.4230/LIPIcs.OPODIS.2019.4},
  annote =	{Keywords: Blockchain, Fairness, Byzantine fault tolerance, Rational players, Equilibrium}
}
Document
DOI: 10.4230/LIPIcs.DISC.2018.7
State Machine Replication Is More Expensive Than Consensus

Authors: Karolos Antoniadis, Rachid Guerraoui, Dahlia Malkhi, and Dragos-Adrian Seredinschi

Published in: LIPIcs, Volume 121, 32nd International Symposium on Distributed Computing (DISC 2018)

Abstract
Consensus and State Machine Replication (SMR) are generally considered to be equivalent problems. In certain system models, indeed, the two problems are computationally equivalent: any solution to the former problem leads to a solution to the latter, and vice versa. In this paper, we study the relation between consensus and SMR from a complexity perspective. We find that, surprisingly, completing an SMR command can be more expensive than solving a consensus instance. Specifically, given a synchronous system model where every instance of consensus always terminates in constant time, completing an SMR command does not necessarily terminate in constant time. This result naturally extends to partially synchronous models. Besides theoretical interest, our result also corresponds to practical phenomena we identify empirically. We experiment with two well-known SMR implementations (Multi-Paxos and Raft) and show that, indeed, SMR is more expensive than consensus in practice. One important implication of our result is that - even under synchrony conditions - no SMR algorithm can ensure bounded response times.
Cite as

Karolos Antoniadis, Rachid Guerraoui, Dahlia Malkhi, and Dragos-Adrian Seredinschi. State Machine Replication Is More Expensive Than Consensus. In 32nd International Symposium on Distributed Computing (DISC 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 121, pp. 7:1-7:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{antoniadis_et_al:LIPIcs.DISC.2018.7,
  author =	{Antoniadis, Karolos and Guerraoui, Rachid and Malkhi, Dahlia and Seredinschi, Dragos-Adrian},
  title =	{{State Machine Replication Is More Expensive Than Consensus}},
  booktitle =	{32nd International Symposium on Distributed Computing (DISC 2018)},
  pages =	{7:1--7:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-092-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{121},
  editor =	{Schmid, Ulrich and Widder, Josef},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2018.7},
  URN =		{urn:nbn:de:0030-drops-97961},
  doi =		{10.4230/LIPIcs.DISC.2018.7},
  annote =	{Keywords: Consensus, State machine replication, Synchronous model}
}
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