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LIPIcs, Volume 361
29th International Conference on Principles of Distributed Systems (OPODIS 2025)
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- published at: 2026-01-07
- Publisher: Schloss Dagstuhl – Leibniz-Zentrum für Informatik
- ISBN: 978-3-95977-409-3
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Complete Volume
LIPIcs, Volume 361, OPODIS 2025, Complete Volume
Abstract
LIPIcs, Volume 361, OPODIS 2025, Complete Volume
Cite as
29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 1-680, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@Proceedings{arusoaie_et_al:LIPIcs.OPODIS.2025,
title = {{LIPIcs, Volume 361, OPODIS 2025, Complete Volume}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {1--680},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025},
URN = {urn:nbn:de:0030-drops-252834},
doi = {10.4230/LIPIcs.OPODIS.2025},
annote = {Keywords: LIPIcs, Volume 361, OPODIS 2025, Complete Volume}
}
Document
Front Matter
Front Matter, Table of Contents, Preface, Conference Organization
Abstract
Front Matter, Table of Contents, Preface, Conference Organization
Cite as
29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 0:i-0:xiv, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{arusoaie_et_al:LIPIcs.OPODIS.2025.0,
author = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael and Tucci-Piergiovanni, Sara},
title = {{Front Matter, Table of Contents, Preface, Conference Organization}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {0:i--0:xiv},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.0},
URN = {urn:nbn:de:0030-drops-252827},
doi = {10.4230/LIPIcs.OPODIS.2025.0},
annote = {Keywords: Front Matter, Table of Contents, Preface, Conference Organization}
}
Document
Invited Talk
SCONE Confidential Computing Environment: Protecting Applications Against Powerful Adversaries (Invited Talk)
Abstract
Our objective is to protect the code, data, and keys of applications against all users with access to the computer systems. In some domains (e.g., healthcare domain), this must be guaranteed, even if the application is not entirely correct. To simplify the adoption of confidential computing, SCONE transforms cloud-native applications into confidential cloud-native applications running on vanilla Kubernetes clusters. The applications can run on Intel SGX, Intel TDX, and AMD SEV. In the near future, SCONE will also support confidential GPUs. The confidentiality, integrity, and consistency of an application’s data and keys are guaranteed by always keeping the data encrypted, i.e., at rest, in transit, and in use. This enables us to add a protection layer around applications to prevent data loss caused be bugs and backdoors in the application code.
Cite as
Christof Fetzer. SCONE Confidential Computing Environment: Protecting Applications Against Powerful Adversaries (Invited Talk). In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, p. 1:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{fetzer:LIPIcs.OPODIS.2025.1,
author = {Fetzer, Christof},
title = {{SCONE Confidential Computing Environment: Protecting Applications Against Powerful Adversaries}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {1:1--1:1},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.1},
URN = {urn:nbn:de:0030-drops-251743},
doi = {10.4230/LIPIcs.OPODIS.2025.1},
annote = {Keywords: trusted execution environments, security}
}
Document
Invited Talk
From Principles to Practice: Algorithmic Insights from Building the Internet Computer (Invited Talk)
Abstract
The theoretical bedrock of distributed computing rests on foundational primitives: peer-to-peer protocols, Byzantine fault tolerance, state machine replication. But what happens when these principles are stretched to a global, evolving, decentralized compute platform intended to host arbitrary applications?
For the past seven years, our work has been dedicated to answering that question through the Internet Computer (IC), a public blockchain network designed for large-scale, general-purpose computation. The IC acts as a stateful serverless cloud[Maksym Arutyunyan et al., 2023], running over 900K applications for millions of users by implementing the Internet Computer Protocol (ICP)[Jan Camenisch et al., 2022] in a sharded, Byzantine-fault-tolerant setup.
This talk explores the algorithmic insights gained from this journey. We will confront where our cherished theoretical models were challenged and had to be radically adapted, composed, or re-imagined. Specifically, we will dive into core problems like:
- Scalable orchestration: Asynchronous and trustless composition of independent state machines.
- Taming Non-Determinism: Designing protocols that allow deterministic replicated state machines to securely query external data.
- The Paradox of Immutability: Enabling stateful upgrades for decentralized applications and even the underlying protocol stack without sacrificing security. I will share the successful design patterns that emerged, detail which core protocols stood the test of time, and which others we overhauled. Finally, I will discuss the hard and sometimes surprising trade-offs we made and pose open research questions to address when designing the next generation of decentralized systems.
Cite as
Yvonne-Anne Pignolet. From Principles to Practice: Algorithmic Insights from Building the Internet Computer (Invited Talk). In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, p. 2:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{pignolet:LIPIcs.OPODIS.2025.2,
author = {Pignolet, Yvonne-Anne},
title = {{From Principles to Practice: Algorithmic Insights from Building the Internet Computer}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {2:1--2:1},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.2},
URN = {urn:nbn:de:0030-drops-251756},
doi = {10.4230/LIPIcs.OPODIS.2025.2},
annote = {Keywords: Internet Computer Protocol, blockchain, state machine replication, Byzantine fault tolerance}
}
Document
Invited Talk
Computing with Content-Oblivious Messages (Invited Talk)
Abstract
One of the core aspects of distributed computing is the design of algorithms that tolerate failures [Cachin et al., 2011; Raynal, 2018]. Failures may involve processes (in which case we may encounter crash-stop, memory corruption, or Byzantine failures) or the communication among processes. When processes communicate through message passing, failures may include message loss, message addition (either duplication or fabrication), and message corruption [Santoro and Widmayer, 1989]. Tight bounds are known for agreement in the synchronous setting under these types of failures [Santoro and Widmayer, 1989], and numerous works have investigated message loss in the synchronous setting and asynchronous setting for many other problems [Herlihy et al., 2013; Raynal, 2018; Santoro and Widmayer, 1990; Schmid et al., 2009].
In this talk, we focus on what can be computed when the system is asynchronous and messages may be corrupted; that is, a sent message can be arbitrarily modified by an adversary, but it cannot be deleted or duplicated. We specifically consider the bleak scenario in which all messages sent by processes are corrupted. Alternatively, one can view this as a setting where all messages have zero size, consisting only of simple pulses. This content-oblivious model is reminiscent of the beeping model [A. Casteigts et al., 2019], but in the beeping model, synchrony allows silence to be used as a means of communication.
Surprisingly, contrary to what one might expect at first glance, [Censor-Hillel et al., 2023] has recently shown that, in the content-oblivious setting, when a predetermined leader is present and the network topology is 2-connected, it is possible to simulate an environment that is completely fault-free.
While [Censor-Hillel et al., 2023] has shown that 2-connectivity is necessary, it also conjectured that the presence of a leader was a required assumption. [Frei et al., 2024] disproved this conjecture for the special case of oriented ring graphs by presenting a composable leader election algorithm. This result was later extended in [Chalopin et al., 2025] to the case of unoriented graphs, and, under the mild assumption of an upper bound on the network size, for any 2-edge-connected network. Thus, for the special case of ring topologies, we have a computational equivalence between content-oblivious and classic asynchronous message passing.
Always in oriented in rings [Chalopin et al., 2025] has shown a non-uniform leader election algorithm with an optimal dependency on process IDs.
The talk will discuss these results, focusing on the open problems and the current state of computation in systems where messages carry no content.
Cite as
Giuseppe Antonio Di Luna. Computing with Content-Oblivious Messages (Invited Talk). In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 3:1-3:2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{diluna:LIPIcs.OPODIS.2025.3,
author = {Di Luna, Giuseppe Antonio},
title = {{Computing with Content-Oblivious Messages}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {3:1--3:2},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.3},
URN = {urn:nbn:de:0030-drops-251766},
doi = {10.4230/LIPIcs.OPODIS.2025.3},
annote = {Keywords: Fault-Tolerance, Message Failures, Simulation, Leader Election, Uniform Algorithms, Non-Uniform Algorithms}
}
Document
A Hierarchy of Unrestricted Deterministic Objects with Consensus Number 1
Abstract
The consensus number of a shared object is the maximum number of processes that can solve consensus in a wait-free manner using copies of the object and registers. In 2016, to prove that an object is not fully characterized by its consensus number, Afek, Ellen and Gafni showed that for all integers n ≥ 2, there exists an infinite sequence of deterministic objects of consensus number n with strictly increasing computational power. In 2018, Daian, Losa, Afek, and Gafni constructed an infinite sequence of deterministic objects of consensus number 1 with strictly decreasing computational power, but the single operation that each of these objects supports is restricted in how it can be used during an execution. As restrictions can have an effect on an object’s consensus number, it was left as an open question whether the same result holds without this restriction.
In this paper, we construct an infinite sequence of unrestricted deterministic objects with strictly decreasing computational power. All objects in this sequence have consensus number 1.
Cite as
Warren Zhu. A Hierarchy of Unrestricted Deterministic Objects with Consensus Number 1. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 4:1-4:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{zhu:LIPIcs.OPODIS.2025.4,
author = {Zhu, Warren},
title = {{A Hierarchy of Unrestricted Deterministic Objects with Consensus Number 1}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {4:1--4:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.4},
URN = {urn:nbn:de:0030-drops-251778},
doi = {10.4230/LIPIcs.OPODIS.2025.4},
annote = {Keywords: Shared Memory, Wait-free, Set Agreement, Consensus Hierarchy}
}
Document
Tight Conditions for Binary-Output Tasks Under Crashes
Abstract
This paper explores necessary and sufficient system conditions to solve distributed tasks with binary outputs (i.e., tasks with output values in {0,1}). We focus on the distinct output sets of values a task can produce (intentionally disregarding validity and value multiplicity), considering that some processes may output no value. In a distributed system with n processes, of which up to t ≤ n can crash, we provide a complete characterization of the tight conditions on n and t under which every class of tasks with binary outputs is solvable, for both synchronous and asynchronous systems. This output-set approach yields highly general results: it unifies multiple distributed computing problems, such as binary consensus and symmetry breaking, and it produces impossibility proofs that hold for stronger task formulations, including those that consider validity, account for value multiplicity, or move beyond binary outputs.
Cite as
Timothé Albouy, Antonio Fernández Anta, Chryssis Georgiou, Nicolas Nicolaou, and Junlang Wang. Tight Conditions for Binary-Output Tasks Under Crashes. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 5:1-5:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{albouy_et_al:LIPIcs.OPODIS.2025.5,
author = {Albouy, Timoth\'{e} and Fern\'{a}ndez Anta, Antonio and Georgiou, Chryssis and Nicolaou, Nicolas and Wang, Junlang},
title = {{Tight Conditions for Binary-Output Tasks Under Crashes}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {5:1--5:24},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.5},
URN = {urn:nbn:de:0030-drops-251786},
doi = {10.4230/LIPIcs.OPODIS.2025.5},
annote = {Keywords: Distributed solvability, Asynchrony, Synchrony, Impossibility proofs, Binary-output tasks, Crash tolerance, Disagreement}
}
Document
Foundations of Fiat-Denominated Loans Collateralized by Cryptocurrencies
Abstract
The rising importance of cryptocurrencies as financial assets pushed their applicability from an object of speculation closer to standard financial instruments such as loans. In this work, we initiate the study of secure protocols that enable fiat-denominated loans collateralized by cryptocurrencies such as Bitcoin. We provide limited-custodial protocols for such loans relying only on trusted arbitration and provide their game-theoretical analysis. We also highlight various interesting directions for future research.
Cite as
Pavel Hubáček, Jan Václavek, and Michelle Yeo. Foundations of Fiat-Denominated Loans Collateralized by Cryptocurrencies. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 6:1-6:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{hubacek_et_al:LIPIcs.OPODIS.2025.6,
author = {Hub\'{a}\v{c}ek, Pavel and V\'{a}clavek, Jan and Yeo, Michelle},
title = {{Foundations of Fiat-Denominated Loans Collateralized by Cryptocurrencies}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {6:1--6:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.6},
URN = {urn:nbn:de:0030-drops-251796},
doi = {10.4230/LIPIcs.OPODIS.2025.6},
annote = {Keywords: Blockchains, Cryptocurrencies, DeFi, Loans, Mechanism design, Subgame Perfect Equilibrium, Rational analysis}
}
Document
Mobile Byzantine Agreement in a Trusted World
Abstract
In this paper, we address the Byzantine Agreement problem in synchronous systems where Byzantine agents can move from process to process, corrupting their host. We focus on two representative models: Garay’s and Buhrman’s models. In Garay’s model, when a process has been left by the Byzantine agent, it enters a cured state, is aware of its condition, and can remain silent for a round to prevent the dissemination of incorrect information. In Buhrman’s model, a Byzantine agent moves together with the message. It has been shown that solving Byzantine Agreement requires at least 4t + 1 processes in Garay’s model, and at least 3t + 1 in Buhrman’s model. In this paper, we aim to increase the tolerance to mobile Byzantine agents by integrating a trusted counter abstraction into both models. This abstraction prevents nodes from equivocating. In the new models, we prove that at least 3t+1, respectively 2t+1 processors are needed to tolerate t mobile Byzantine agents. Furthermore, we propose novel Mobile Byzantine Agreement algorithms that match these new lower bounds for both Garay’s and Buhrman’s models, achieving agreement in 𝒪(n) synchronous rounds.
Cite as
Bo Pan and Maria Potop-Butucaru. Mobile Byzantine Agreement in a Trusted World. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 7:1-7:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{pan_et_al:LIPIcs.OPODIS.2025.7,
author = {Pan, Bo and Potop-Butucaru, Maria},
title = {{Mobile Byzantine Agreement in a Trusted World}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {7:1--7:20},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.7},
URN = {urn:nbn:de:0030-drops-251809},
doi = {10.4230/LIPIcs.OPODIS.2025.7},
annote = {Keywords: Byzantine Agreement, Mobile Faults, Trusted Abstractions}
}
Document
Weaker Assumptions for Asymmetric Trust
Abstract
In distributed systems with asymmetric trust, each participant is free to make its own trust assumptions about others, captured by an asymmetric quorum system. This contrasts with ordinary, symmetric quorum systems and threshold models, where trust assumptions are uniformly shared among participants. Fundamental problems like reliable broadcast and consensus are unsolvable in the asymmetric model if quorum systems satisfy only the classical properties of consistency and availability. Existing approaches overcome this by introducing stronger assumptions. We show that some of these assumptions are overly restrictive, so much so that they effectively eliminate the benefits of asymmetric trust. To address this, we propose a new approach to characterize asymmetric problems and, building upon it, present algorithms for reliable broadcast and consensus that require weaker assumptions than previous solutions. Our methods are general and can be extended to other core problems in systems with asymmetric trust.
Cite as
Ignacio Amores-Sesar, Christian Cachin, Simon Holmgaard Kamp, and Juan Villacis. Weaker Assumptions for Asymmetric Trust. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 8:1-8:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{amoressesar_et_al:LIPIcs.OPODIS.2025.8,
author = {Amores-Sesar, Ignacio and Cachin, Christian and Kamp, Simon Holmgaard and Villacis, Juan},
title = {{Weaker Assumptions for Asymmetric Trust}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {8:1--8:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.8},
URN = {urn:nbn:de:0030-drops-251812},
doi = {10.4230/LIPIcs.OPODIS.2025.8},
annote = {Keywords: Asymmetric Trust, Quorum Systems, Reliable Broadcast, Consensus}
}
Document
Contention-Aware Cooperation
Abstract
As shown by Reliable Broadcast and Consensus, cooperation among a set of independent computing entities (sequential processes) is crucial in fault-tolerant distributed computing. Considering n-process asynchronous message-passing systems where some processes may be Byzantine, this paper introduces a novel cooperation abstraction, Contention-Aware Cooperation (CAC). While Reliable Broadcast is a one-to-n cooperation abstraction and Consensus is an n-to-n cooperation abstraction, CAC is a d-to-n cooperation abstraction where d (1 ≤ d ≤ n) varies with each run and remains unknown to the processes. Correct processes accept the same set of 𝓁 pairs ⟨ v,i ⟩ (v is the value proposed by p_i) from the d proposer processes, where 1 ≤ 𝓁 ≤ d and (as d) 𝓁 remains unknown to the processes (except in specific cases). Those 𝓁 values are accepted one at a time, potentially in different orders at each process. In addition, CAC provides each process with an imperfect oracle that provides insights into the values that they may accept in the future. Interestingly, the CAC abstraction is particularly efficient in favorable circumstances, when the oracle becomes accurate, which processes can detect. To illustrate its practical utility, the paper details two applications leveraging CAC: a fast consensus implementation optimized for low contention (named Cascading Consensus), and a novel naming problem that can be solved under full asynchrony. All algorithms presented require signatures.
Cite as
Timothé Albouy, Davide Frey, Mathieu Gestin, Michel Raynal, and François Taïani. Contention-Aware Cooperation. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 9:1-9:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{albouy_et_al:LIPIcs.OPODIS.2025.9,
author = {Albouy, Timoth\'{e} and Frey, Davide and Gestin, Mathieu and Raynal, Michel and Ta\"{i}ani, Fran\c{c}ois},
title = {{Contention-Aware Cooperation}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {9:1--9:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.9},
URN = {urn:nbn:de:0030-drops-251823},
doi = {10.4230/LIPIcs.OPODIS.2025.9},
annote = {Keywords: Agreement, Asynchronous message-passing system, Byzantine processes, Conflict detection, Consensus, Cooperation abstraction, Distributed computing, Fault tolerance, Optimistically terminating consensus, Short-naming}
}
Document
Computing in a Faulty Congested Clique
Abstract
We study a Faulty Congested Clique model, in which an adversary may fail nodes in the network throughout the computation. We show that any task of O(nlog{n})-bit input per node can be solved in roughly n rounds, where n is the size of the network. This nearly matches the linear upper bound on the complexity of the non-faulty Congested Clique model for such problems, by learning the entire input, and it holds in the faulty model even with a linear number of faults.
Our main contribution is that we establish that one can do much better by looking more closely at the computation. Given a deterministic algorithm 𝒜 for the non-faulty Congested Clique model, we show how to transform it into an algorithm 𝒜' for the faulty model, with an overhead that could be as small as some logarithmic-in-n factor, by considering refined complexity measures of 𝒜.
As an exemplifying application of our approach, we show that the O(n^{1/3})-round complexity of semi-ring matrix multiplication [Censor{-}Hillel, Kaski, Korhonen, Lenzen, Paz, Suomela, PODC 2015] remains the same up to polylog factors in the faulty model, even if the adversary can fail 99% of the nodes (or any other constant fraction).
Cite as
Keren Censor-Hillel and Pedro Soto. Computing in a Faulty Congested Clique. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 10:1-10:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{censorhillel_et_al:LIPIcs.OPODIS.2025.10,
author = {Censor-Hillel, Keren and Soto, Pedro},
title = {{Computing in a Faulty Congested Clique}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {10:1--10:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.10},
URN = {urn:nbn:de:0030-drops-251833},
doi = {10.4230/LIPIcs.OPODIS.2025.10},
annote = {Keywords: distributed computing, graph algorithms, computing with faults}
}
Document
Formalizing Rollback Netcodes for Robust and Real-Time Client-Server Architectures
Abstract
The rapid growth of the gaming industry has made netcodes (the part of an online game’s source code that handles networking and synchronization) a critical component of the online multiplayer experience. Among various approaches, rollback netcodes have become a popular choice for real-time games due to their ability to enhance responsiveness and player immersion. However, despite their widespread adoption, these netcodes remain susceptible to subtle latency-based attacks that can be challenging to detect. Notably, while rollback netcodes play a critical role in the gaming industry and share similarities with synchronization mechanisms in distributed systems, they have received relatively limited attention in academic research.
In this work, we present a formal specification of rollback netcodes and identify key behavioral properties and requirements to strengthen their resilience against latency-based attacks that are prevalent in gaming, such as lag-switch and DDoS attacks. Our analysis allows us to explore the trade-offs between preserving immersive gameplay and ensuring security. Our findings reveal that ideal immersion requires strict assumptions about network latency, which are unattainable in adversarial environments where message delays are inevitable.
Cite as
Yérom-David Bromberg, Jérémie Decouchant, Manon Sourisseau, and François Taïani. Formalizing Rollback Netcodes for Robust and Real-Time Client-Server Architectures. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 11:1-11:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{bromberg_et_al:LIPIcs.OPODIS.2025.11,
author = {Bromberg, Y\'{e}rom-David and Decouchant, J\'{e}r\'{e}mie and Sourisseau, Manon and Ta\"{i}ani, Fran\c{c}ois},
title = {{Formalizing Rollback Netcodes for Robust and Real-Time Client-Server Architectures}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {11:1--11:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.11},
URN = {urn:nbn:de:0030-drops-251841},
doi = {10.4230/LIPIcs.OPODIS.2025.11},
annote = {Keywords: Online Multiplayer Game, Rollback Netcode, Network Security, Latency attacks}
}
Document
Efficient Byzantine Reliable Broadcast in the Failure Case
Abstract
Reliable broadcast is a fundamental primitive in distributed computing that is widely used in various applications. Several new reliable broadcast algorithms have been presented in recent years, primarily focusing on reducing the communication complexity, which is the total number of exchanged bits in the worst case. While significant progress has been achieved, all proposed algorithms share a common weakness. Executions may fail, i.e., no message is ever delivered, while incurring a communication complexity equal or nearly equal to the communication complexity of executions where a message is delivered. In fact, a single Byzantine node, acting as the dedicated sender, is sufficient to trigger such executions, causing all nodes to consume bandwidth in vain.
This paper introduces the novel concept of a reliable broadcast detector, a distributed algorithm that can be coupled with a reliable broadcast algorithm to minimize the communication complexity of failed executions. Two concrete detectors are presented with different requirements and properties. Additionally, reliable broadcast algorithms that utilize detectors are introduced, the main algorithm guaranteeing an overhead factor, compared to an ideal failure-free execution, that tends to 2 as the network size increases. Furthermore, a lower bound is proven that an overhead factor of 5/3 is inevitable when the sender initially broadcasts the message, as is the case for the proposed algorithm. Therefore, it achieves a bound that is close to optimal for any algorithm with this property.
Cite as
Thomas Locher. Efficient Byzantine Reliable Broadcast in the Failure Case. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 12:1-12:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{locher:LIPIcs.OPODIS.2025.12,
author = {Locher, Thomas},
title = {{Efficient Byzantine Reliable Broadcast in the Failure Case}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {12:1--12:20},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.12},
URN = {urn:nbn:de:0030-drops-251854},
doi = {10.4230/LIPIcs.OPODIS.2025.12},
annote = {Keywords: asynchronous networks, reliable broadcast, communication complexity}
}
Document
A General Input-Dependent Colorless Computability Theorem and Applications to Core-Dependent Adversaries
Abstract
Distributed computing tasks can be presented with a triple (ℐ,𝒪,Δ). The solvability of a colorless task on the Iterated Immediate Snapshot model (IIS) has been characterized by the Colorless Computability Theorem [Maurice Herlihy et al., 2013]. A recent paper [Yannis Coutouly and Emmanuel Godard, 2024] generalizes this theorem for any message adversaries ℳ ⊆ IIS by geometric methods.
In 2001, Mostéfaoui, Rajsbaum, Raynal, and Roy [Achour Mostéfaoui et al., 2002] introduced condition-based adversaries. This setting considers a particular adversary that will be applied only to a subset of input configurations. In this setting, they studied the k-set agreement task with condition-based t-resilient adversaries and obtained a sufficient condition on the conditions that make k-Set Agreement solvable.
In this paper we have three contributions:
1) We generalize the characterization of [Yannis Coutouly and Emmanuel Godard, 2024] to input-dependent adversaries, which means that the adversaries can change depending on the input configuration.
2) We show that core-resilient adversaries of IIS_n have the same computability power as the core-resilient adversaries of IIS_n where crashes only happen at the start.
3) Using the two previous contributions, we provide a necessary and sufficient characterization of the condition-based, core-dependent adversaries that can solve k-Set Agreement.
We also distinguish four settings that may appear when presenting a distributed task as (ℐ,𝒪,Δ). Finally, in a later section, we present structural properties on the carrier map Δ. Such properties allow simpler proof, without changing the computability power of the task. Most of the proofs in this article leverage the topological framework used in distributed computing by using simple geometric constructions.
Cite as
Yannis Coutouly and Emmanuel Godard. A General Input-Dependent Colorless Computability Theorem and Applications to Core-Dependent Adversaries. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 13:1-13:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{coutouly_et_al:LIPIcs.OPODIS.2025.13,
author = {Coutouly, Yannis and Godard, Emmanuel},
title = {{A General Input-Dependent Colorless Computability Theorem and Applications to Core-Dependent Adversaries}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {13:1--13:21},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.13},
URN = {urn:nbn:de:0030-drops-251862},
doi = {10.4230/LIPIcs.OPODIS.2025.13},
annote = {Keywords: colorless task, topological methods, geometric simplicial complex, k-set-agreement, t-resilient model, condition-based computability}
}
Document
Optimal-Length Labeling Schemes for Fast Deterministic Communication in Radio Networks
Abstract
We consider two fundamental communication tasks in arbitrary radio networks: broadcasting (information from one source has to reach all nodes) and gossiping (every node has a message and all messages have to reach all nodes). Nodes are assigned labels that are (not necessarily different) binary strings. Each node knows its own label and can use it as a parameter in the same deterministic algorithm. The length of a labeling scheme is the largest length of a label. The goal is to find labeling schemes of asymptotically optimal length for the above tasks, and to design fast deterministic distributed algorithms for each of them, using labels of optimal length.
Our main result concerns broadcasting. We show the existence of a labeling scheme of constant length that supports broadcasting in time O(D+log² n), where D is the diameter of the network and n is the number of nodes. This broadcasting time is an improvement over the best currently known O(Dlog n + log² n) time of broadcasting with constant-length labels, due to Ellen and Gilbert (SPAA 2020). It also matches the optimal broadcasting time in radio networks of known topology. Hence, we show that appropriately chosen node labels of constant length permit to achieve, in a distributed way, the optimal centralized broadcasting time. This is, perhaps, the most surprising finding of this paper. We are able to obtain our result thanks to a novel methodological tool of propagating information in radio networks, that we call a 2-height respecting tree.
Next, we apply our broadcasting algorithm to solve the gossiping problem. We get a gossiping algorithm working in time O(D + Δlog n + log² n), using a labeling scheme of optimal length O(log Δ), where Δ is the maximum degree. Our time is the same as the best known gossiping time in radio networks of known topology.
Cite as
Adam Ganczorz, Tomasz Jurdzinski, and Andrzej Pelc. Optimal-Length Labeling Schemes for Fast Deterministic Communication in Radio Networks. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 14:1-14:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{ganczorz_et_al:LIPIcs.OPODIS.2025.14,
author = {Ganczorz, Adam and Jurdzinski, Tomasz and Pelc, Andrzej},
title = {{Optimal-Length Labeling Schemes for Fast Deterministic Communication in Radio Networks}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {14:1--14:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.14},
URN = {urn:nbn:de:0030-drops-251874},
doi = {10.4230/LIPIcs.OPODIS.2025.14},
annote = {Keywords: radio network, distributed algorithms, algorithms with advice, labeling scheme, broadcasting, gossiping}
}
Document
Time-Optimal and Energy-Efficient Deterministic Consensus
Abstract
We study fault-tolerant consensus in a variant of the synchronous message passing model, where, in each round, every node can choose to be awake or asleep. This is known as the sleeping model (Chatterjee, Gmyr, Pandurangan PODC 2020) and defines the awake complexity (also called energy complexity), which measures the maximum number of rounds that any node is awake throughout the execution. Only awake nodes can send and receive messages in a given round and all messages sent to sleeping nodes are lost. We present new deterministic consensus algorithms that tolerate up to f < n crash failures, where n is the number of nodes. Our algorithms match the optimal time complexity lower bound of f+1 rounds. For multi-value consensus, where the input values are chosen from some possibly large set, we achieve an energy complexity of 𝒪(⌈ f² / n ⌉) rounds, whereas for binary consensus, we show an algorithm to achieve 𝒪(⌈ f / √n ⌉) energy complexity.
Cite as
Shachar Meir, Hugo Mirault, David Peleg, and Peter Robinson. Time-Optimal and Energy-Efficient Deterministic Consensus. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 15:1-15:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{meir_et_al:LIPIcs.OPODIS.2025.15,
author = {Meir, Shachar and Mirault, Hugo and Peleg, David and Robinson, Peter},
title = {{Time-Optimal and Energy-Efficient Deterministic Consensus}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {15:1--15:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.15},
URN = {urn:nbn:de:0030-drops-251881},
doi = {10.4230/LIPIcs.OPODIS.2025.15},
annote = {Keywords: Distributed computing, Crash faults, Consensus, Energy complexity, Sleeping model}
}
Document
Asynchronous Approximate Agreement with Quadratic Communication
Abstract
We study approximate agreement in an asynchronous network of n parties, up to t of which are byzantine. This an agreement task where the parties obtain approximately equal inputs in the convex hull of their inputs. In an asynchronous network, it can be solved with the optimal resilience t < n/3 by forcing the parties to reliably broadcast their messages and thus preventing inconsistent byzantine behavior. This costs Θ(n²) messages per reliable broadcast, or Θ(n³) messages per protocol iteration.
In this work, we forgo reliable broadcast to achieve asynchronous approximate agreement against t < n/3 faults with quadratic communication. In a tree with the maximum degree Δ and the centroid decomposition height h, we achieve edge agreement (agreement on two adjacent vertices) in at most 6h + 1 rounds with 𝒪(n²) messages of size 𝒪(log Δ + log h) per round. We do this by designing a 6-round multivalued 2-graded consensus protocol and using it to construct a recursive edge agreement protocol. Then, we achieve edge agreement in the infinite path ℤ, again by using 2-graded consensus. Finally, we show that our edge agreement protocol enables approximate agreement in ℝ (with outputs that are at most some small parameter ε > 0 apart) in 6log₂M/(ε) + 𝒪(log log M/(ε)) rounds with 𝒪(n²) messages of size 𝒪(log log M/(ε)) per round, where M is the maximum non-byzantine input magnitude.
Cite as
Mose Mizrahi Erbes and Roger Wattenhofer. Asynchronous Approximate Agreement with Quadratic Communication. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 16:1-16:26, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{mizrahierbes_et_al:LIPIcs.OPODIS.2025.16,
author = {Mizrahi Erbes, Mose and Wattenhofer, Roger},
title = {{Asynchronous Approximate Agreement with Quadratic Communication}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {16:1--16:26},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.16},
URN = {urn:nbn:de:0030-drops-251890},
doi = {10.4230/LIPIcs.OPODIS.2025.16},
annote = {Keywords: Approximate agreement, byzantine fault tolerance, communication complexity}
}
Document
Recoverable Lock-Free Locks
Abstract
This paper presents the first transformation that introduces both lock-freedom and recoverability. Our transformation starts with a lock-based implementation, and provides a recoverable, lock-free substitution to lock acquire and lock release operations. The transformation supports nested locks for generality and ensures recoverability without jeopardising the correctness of the lock-based implementation it is applied on.
Cite as
Hagit Attiya, Panagiota Fatourou, Eleftherios Kosmas, and Yuanhao Wei. Recoverable Lock-Free Locks. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 17:1-17:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{attiya_et_al:LIPIcs.OPODIS.2025.17,
author = {Attiya, Hagit and Fatourou, Panagiota and Kosmas, Eleftherios and Wei, Yuanhao},
title = {{Recoverable Lock-Free Locks}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {17:1--17:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.17},
URN = {urn:nbn:de:0030-drops-251905},
doi = {10.4230/LIPIcs.OPODIS.2025.17},
annote = {Keywords: recoverable computing, NVM, lock, lock-freedom}
}
Document
Distributed Download from an External Data Source in Asynchronous Faulty Settings
Abstract
The distributed Data Retrieval (DR) model consists of k peers connected by a complete peer-to-peer communication network, and a trusted external data source that stores an array X of n bits (n ≫ k). Up to β k of the peers might fail in any execution (for β ∈ [0, 1)). Peers can obtain the information either by inexpensive messages passed among themselves or through expensive queries to the source array X. In the DR model, we focus on designing protocols that minimize the number of queries performed by any nonfaulty peer (a measure referred to as the query complexity) while maximizing the resiliency parameter β.
The Download problem requires each nonfaulty peer to correctly learn the entire array X. Earlier work on this problem focused on synchronous communication networks and established several deterministic and randomized upper and lower bounds. Our work is the first to extend the study of distributed data retrieval to asynchronous communication networks. We address the Download problem under both the Byzantine and crash failure models. We present query-optimal deterministic solutions in an asynchronous model that can tolerate any fixed fraction β < 1 of crash faults. In the Byzantine failure model, it is known that deterministic protocols incur a query complexity of Ω(n) per peer, even under synchrony. We extend this lower bound to randomized protocols in the asynchronous model for β ≥ 1/2, and further show that for β < 1/2, a randomized protocol exists with near-optimal query complexity.
Cite as
John Augustine, Soumyottam Chatterjee, Valerie King, Manish Kumar, Shachar Meir, and David Peleg. Distributed Download from an External Data Source in Asynchronous Faulty Settings. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 18:1-18:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{augustine_et_al:LIPIcs.OPODIS.2025.18,
author = {Augustine, John and Chatterjee, Soumyottam and King, Valerie and Kumar, Manish and Meir, Shachar and Peleg, David},
title = {{Distributed Download from an External Data Source in Asynchronous Faulty Settings}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {18:1--18:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.18},
URN = {urn:nbn:de:0030-drops-251915},
doi = {10.4230/LIPIcs.OPODIS.2025.18},
annote = {Keywords: Byzantine Fault Tolerance, Blockchain Oracle, Data Retrieval Model, Distributed Download, asynchrony}
}
Document
Orientation Does Not Help with 3-Coloring a Grid in Online-LOCAL
Abstract
The online-LOCAL and SLOCAL models are extensions of the LOCAL model where nodes are processed in a sequential but potentially adversarial order. So far, the only problem we know of where the global memory of the online-LOCAL model has an advantage over SLOCAL is 3-coloring bipartite graphs. Recently, Chang et al. [PODC 2024] showed that even in grids, 3-coloring requires Ω(log n) locality in deterministic online-LOCAL. This result was subsequently extended by Akbari et al. [STOC 2025] to also hold in randomized online-LOCAL. However, both proofs heavily rely on the assumption that the algorithm does not have access to the orientation of the underlying grid. In this paper, we show how to lift this requirement and obtain the same lower bound (against either model) even when the algorithm is explicitly given a globally consistent orientation of the grid.
Cite as
Thomas Boudier, Filippo Casagrande, Avinandan Das, Massimo Equi, Henrik Lievonen, Augusto Modanese, and Ronja Stimpert. Orientation Does Not Help with 3-Coloring a Grid in Online-LOCAL. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 19:1-19:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{boudier_et_al:LIPIcs.OPODIS.2025.19,
author = {Boudier, Thomas and Casagrande, Filippo and Das, Avinandan and Equi, Massimo and Lievonen, Henrik and Modanese, Augusto and Stimpert, Ronja},
title = {{Orientation Does Not Help with 3-Coloring a Grid in Online-LOCAL}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {19:1--19:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.19},
URN = {urn:nbn:de:0030-drops-251925},
doi = {10.4230/LIPIcs.OPODIS.2025.19},
annote = {Keywords: coloring, locally checkable labeling problems, online algorithms}
}
Document
Fast Rerouting Against Dynamic Failures: 2-Resilience via Ear-Decomposition and Planarity
Abstract
Modern communication networks employ local fast failover mechanisms in the data plane, swiftly reacting to link failures through pre-installed rerouting rules. This paper investigates resilient routing schemes that guarantee packet delivery under up to k link failures, provided the source and destination remain connected in the degraded network. While prior theoretical studies have mainly addressed static failures, where multiple links fail simultaneously and permanently, real networks often experience dynamic failures, such as transient link flapping caused by short-lived faults.
We study the limits of basic and source-matched failover routing with packet-header rewriting against dynamic failures in general graphs. In basic routing, forwarding depends only on active links, incoming ports, and the destination, whereas source-matched routing additionally incorporates the source, requiring more memory (and logic) at the router. The 2-resilient source-matched routing for static failures is shown to fail under permanent but non-simultaneous failures. Moreover, even with source matching, we prove that in planar graphs k ≥ 2 resilience is impossible without bit rewriting, and in general graphs, perfect k-resilience is unachievable by only rewriting O(log k) bits.
For planar graphs, we introduce ear-decomposition into basic routing and develop novel local rerouting mechanisms that tolerate dynamic failures. These yield tight 2-resilient basic routing by rewriting only one or two bits, closing the gap between lower bounds and practical routing scheme.
Cite as
Wenkai Dai, Klaus-Tycho Foerster, and Stefan Schmid. Fast Rerouting Against Dynamic Failures: 2-Resilience via Ear-Decomposition and Planarity. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 20:1-20:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{dai_et_al:LIPIcs.OPODIS.2025.20,
author = {Dai, Wenkai and Foerster, Klaus-Tycho and Schmid, Stefan},
title = {{Fast Rerouting Against Dynamic Failures: 2-Resilience via Ear-Decomposition and Planarity}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {20:1--20:20},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.20},
URN = {urn:nbn:de:0030-drops-251930},
doi = {10.4230/LIPIcs.OPODIS.2025.20},
annote = {Keywords: Resilience, Local Failover, Routing, Dynamic Link Failures, Link Flapping}
}
Document
Solving Tasks with Fewer Registers Than Processes
Abstract
This paper studies distributed-computing tasks through the lens of space complexity in the read/write wait-free model, defined as the number of multi-reader-multi-writer atomic read/write registers needed to solve a task using a wait-free algorithm. Surprisingly, even though the read/write wait-free model is at the foundation of distributed computing, previous work on space complexity has focused on synchronization primitives stronger than read/write registers or on weaker progress conditions.
The paper reveals that the read/write wait-free model offers a rich space-complexity landscape: (1) assuming non-anonymous processes, it shows that there is an infinite hierarchy of tasks of increasing space complexity; (2) it shows that space complexity separates anonymous from non-anonymous memory; (3) regardless of process or register anonymity, it exhibits a task of space complexity two, which is the minimal non-trivial space complexity; (4) finally, it shows that subcases of the adopt-commit task have different space complexity in non-anonymous memory under bounded wait-freedom.
Cite as
Eli Gafni, Giuliano Losa, Michel Raynal, and Gadi Taubenfeld. Solving Tasks with Fewer Registers Than Processes. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 21:1-21:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{gafni_et_al:LIPIcs.OPODIS.2025.21,
author = {Gafni, Eli and Losa, Giuliano and Raynal, Michel and Taubenfeld, Gadi},
title = {{Solving Tasks with Fewer Registers Than Processes}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {21:1--21:21},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.21},
URN = {urn:nbn:de:0030-drops-251947},
doi = {10.4230/LIPIcs.OPODIS.2025.21},
annote = {Keywords: Asynchrony, Read/write registers, Wait-freedom, Tasks, Covering argument, Lower bound, Space complexity, Anonymous Processes, Anonymous Memory}
}
Document
Making Democracy Work: Fixing and Simplifying Egalitarian Paxos
Abstract
Classical state-machine replication protocols, such as Paxos, rely on a distinguished leader process to order commands. Unfortunately, this approach makes the leader a single point of failure and increases the latency for clients that are not co-located with it. As a response to these drawbacks, Egalitarian Paxos [Iulian Moraru et al., 2013] introduced an alternative, leaderless approach, that allows replicas to order commands collaboratively. Not relying on a single leader allows the protocol to maintain non-zero throughput with up to f crashes of any processes out of a total of n = 2f+1. The protocol furthermore allows any process to execute a command c fast, in 2 message delays, provided no more than e = ⌈(f+1)/2⌉ other processes fail, and all concurrently submitted commands commute with c; the latter condition is often satisfied in practical systems.
Egalitarian Paxos has served as a foundation for many other replication protocols. But unfortunately, the protocol is very complex, ambiguously specified and suffers from nontrivial bugs. In this paper, we present EPaxos* - a simpler and correct variant of Egalitarian Paxos. Our key technical contribution is a simpler failure-recovery algorithm, which we have rigorously proved correct. Our protocol also generalizes Egalitarian Paxos to cover the whole spectrum of failure thresholds f and e such that n ≥ max{2e+f-1, 2f+1} - the number of processes that we show to be optimal.
Cite as
Fedor Ryabinin, Alexey Gotsman, and Pierre Sutra. Making Democracy Work: Fixing and Simplifying Egalitarian Paxos. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 22:1-22:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{ryabinin_et_al:LIPIcs.OPODIS.2025.22,
author = {Ryabinin, Fedor and Gotsman, Alexey and Sutra, Pierre},
title = {{Making Democracy Work: Fixing and Simplifying Egalitarian Paxos}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {22:1--22:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.22},
URN = {urn:nbn:de:0030-drops-251955},
doi = {10.4230/LIPIcs.OPODIS.2025.22},
annote = {Keywords: Consensus, state-machine replication, fault tolerance}
}
Document
Distributed (Δ+1)-Coloring in Graphs of Bounded Neighborhood Independence
Abstract
The distributed coloring problem is arguably one of the key problems studied in the area of distributed graph algorithms. The most standard variant of the problem asks for a proper vertex coloring of a graph with Δ+1 colors, where Δ is the maximum degree of the graph. Despite an immense amount of work on distributed coloring problems in the distributed setting, determining the deterministic complexity of (Δ+1)-coloring in the standard message passing model remains one of the most important open questions of the area. In the LOCAL model, it is known that (Δ+1)-coloring requires Ω(log^* n) rounds even in paths and rings (i.e., when Δ = 2). For general graphs, the problem is known to be solvable in Õ(log^{5/3}n) rounds and in O(√{ΔlogΔ} + log^* n) rounds when expressing the complexity as a function of Δ and with an optimal dependency on n. In the present paper, we aim to improve our understanding of the deterministic complexity of (Δ+1)-coloring as a function of Δ in a special family of graphs for which significantly faster algorithms are already known.
The neighborhood independence θ of a graph is the maximum number of pairwise non-adjacent neighbors of some node of the graph. Notable examples of graphs of bounded neighborhood independence are line graphs of graphs and bounded-rank hypergraphs. It is known that the (2Δ-1)-edge coloring problem and therefore the (Δ+1)-coloring problem in line graphs of graphs can be solved in O(log^{12}Δ+log^* n) rounds. In general, in graphs of neighborhood independence θ = O(1), it is known that (Δ+1)-coloring can be solved in 2^{O(√{logΔ})}+O(log^* n) rounds. In the present paper, we significantly improve the latter result, and we show that in graphs of neighborhood independence θ, a (Δ+1)-coloring can be computed in (θ⋅logΔ)^{O(log logΔ / log log logΔ)}+O(log^* n) rounds and thus in quasipolylogarithmic time in Δ as long as θ is at most polylogarithmic in Δ. Our algorithm can be seen as a generalization of an existing similar, but slightly weaker result for (2Δ-1)-edge coloring. We also show that the approach that leads to this polylogarithmic in Δ algorithm for (2Δ-1)-edge coloring already fails for edge colorings of hypergraphs of rank at least 3. At the core of the fast edge coloring algorithm is an algorithm to divide the edges of a graph into two parts so that up to a multiplicative error of 1+o(1), the maximum degree of the line graph induced by each part is at most half the maximum degree of the original line graph. We show that computing such a bipartition of the edges of the line graph of a hypergraph of rank at least 3 requires time logarithmic in n.
Cite as
Marc Fuchs and Fabian Kuhn. Distributed (Δ+1)-Coloring in Graphs of Bounded Neighborhood Independence. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 23:1-23:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{fuchs_et_al:LIPIcs.OPODIS.2025.23,
author = {Fuchs, Marc and Kuhn, Fabian},
title = {{Distributed (\Delta+1)-Coloring in Graphs of Bounded Neighborhood Independence}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {23:1--23:21},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.23},
URN = {urn:nbn:de:0030-drops-251968},
doi = {10.4230/LIPIcs.OPODIS.2025.23},
annote = {Keywords: distributed computing, distributed graph algorithms, graph coloring, list coloring, defective coloring}
}
Document
On Time-Optimal, Fault-Tolerant Algorithms for Connected Consensus Beyond Grade Two
Abstract
A common question in the asynchronous model is whether some given notion of agreement between processes is achievable. Usually, we formalise such agreement notions in the form of agreement problems. Some of these problems also receive the name of coordination primitives. Several fault-tolerant algorithms in asynchronous systems rely upon the use of different primitives as building blocks, such as adopt-commit, crusader agreement, or graded broadcast.
Recently, the connected consensus problem - a form of agreement over a specific family of graphs parametrised by a positive integer R- was introduced. This problem unifies the three mentioned primitives while extending them for multi-valued inputs. Moreover, the problem is equipped with a security condition called binding, which limits the effect of malicious processes over the decision of correct parties. While fault-tolerant connected consensus algorithms for R = 1 and R = 2 are known, the existence of algorithmic solutions for any positive integer parameter remained an open question.
In this work, we introduce a pair of fault-tolerant algorithms for connected consensus when the R parameter is any positive integer. We introduce a crash-resilient algorithm, which is optimal with respect to the maximum number of possible faulty processes. Our second algorithm is resilient to Byzantine failures; whose failure-resilience is optimal for a specific class of algorithms. Both algorithms satisfy the binding property and match the best known time complexities achieved for the R = 1 and R = 2 cases, further achieving time optimality for the general case in the crash-failure setting, and asymptotic time optimality in the Byzantine scenario.
Cite as
Alan Ernesto Arteaga Vázquez. On Time-Optimal, Fault-Tolerant Algorithms for Connected Consensus Beyond Grade Two. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 24:1-24:28, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{arteagavazquez:LIPIcs.OPODIS.2025.24,
author = {Arteaga V\'{a}zquez, Alan Ernesto},
title = {{On Time-Optimal, Fault-Tolerant Algorithms for Connected Consensus Beyond Grade Two}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {24:1--24:28},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.24},
URN = {urn:nbn:de:0030-drops-251973},
doi = {10.4230/LIPIcs.OPODIS.2025.24},
annote = {Keywords: Approximate Agreement, Binding, Connected Consensus}
}
Document
On the Complexity of Distributed Edge Coloring and Orientation Problems
Abstract
Understanding the role of randomness when solving locally checkable labeling (LCL) problems in the LOCAL model has been one of the top priorities in the research on distributed graph algorithms in recent years. For LCL problems in bounded-degree graphs, it is known that randomness cannot help more than polynomially, except in one case: if the deterministic complexity of an LCL problem is in Ω(log n) and its randomized complexity is in o(log n), then the randomized complexity is guaranteed to be O(poly(log log n)) and it is even known to be O(log log n) in bounded-degree trees. However, the fundamental question of which problems with a deterministic complexity of Ω(log n) can be solved exponentially faster using randomization still remains wide open.
We make a step towards answering this question by studying a simple, but natural class of LCL problems: so-called degree splitting problems. These problems come in two varieties: coloring problems where the edges of a graph have to be colored with 2 colors and orientation problems where each edge needs to be oriented. For an exact classification, it is most natural to consider the Δ-regular case (for Δ = O(1)), where we obtain the following results.
- We exactly characterize the complexity of problems where the edges need to be colored with two colors, say red and blue. We show that for every y ∈ {0,… ,Δ-1}, the problem of red-blue coloring the edges such that every node of degree Δ has either y or y+1 red edges has randomized complexity O(log log n) in general graphs of maximum degree Δ. Any other problem, i.e., any problem that does not allow two consecutive red degrees, is already known to have randomized complexity Ω(log n) even in Δ-regular trees. We note that a set of edges F such that every node has either y or y+1 incident edges in F is also known as a {y,y+1}-factor of a graph.
- For edge orientations, we show that for any two r₁ and r₂ such that r₁,r₂ ≤ Δ/2 and r₁+r₂ ≥ Δ/2, there are randomized algorithms with round complexities O(log log n) in trees and Õ(log⁴log n) in general graphs to compute an edge orientation such that all nodes have outdegree r₁ ± O(√{ΔlogΔ}) or Δ-r₂ ± O(√{ΔlogΔ}). Further, there exists a constant c > 0 such that for any 0 ≤ r₁+r₂ ≤ Δ/2, the problem of computing an edge orientation in which all outdegrees are either at most r₁-c⋅ √{Δ} or at least Δ-r₂+c⋅√{Δ} has randomized complexity Ω(log n) even in Δ-regular trees.
While our results are cleanest to state for the Δ-regular case, all our algorithms naturally generalize to nodes of any degree d < Δ in general graphs of maximum degree Δ. All our algorithms also naturally generalize to the unbounded degree case and they then have a randomized complexity of Õ(Δ) ⋅ log log n (resp. Õ(Δ ⋅log⁴log n) for orienting general graphs).
Cite as
Sebastian Brandt, Fabian Kuhn, and Zahra Parsaeian. On the Complexity of Distributed Edge Coloring and Orientation Problems. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 25:1-25:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{brandt_et_al:LIPIcs.OPODIS.2025.25,
author = {Brandt, Sebastian and Kuhn, Fabian and Parsaeian, Zahra},
title = {{On the Complexity of Distributed Edge Coloring and Orientation Problems}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {25:1--25:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.25},
URN = {urn:nbn:de:0030-drops-251982},
doi = {10.4230/LIPIcs.OPODIS.2025.25},
annote = {Keywords: LCL problems, binary labeling problems, degree splitting}
}
Document
Recognizing Hereditary Properties in the Presence of Byzantine Nodes
Abstract
Augustine et al. [DISC 2022] initiated the study of distributed graph algorithms in the presence of Byzantine nodes in the congested clique model. In this model, there is a set B of Byzantine nodes, where |B| is less than a third of the total number of nodes. These nodes have complete knowledge of the network and the state of other nodes, and they conspire to alter the output of the system. The authors addressed the connectivity problem, showing that it is solvable under the promise that either the subgraph induced by the honest nodes is connected, or the graph has 2|B|+1 connected components.
In the current work, we continue the study of the Byzantine congested clique model by considering the recognition of other graph properties, specifically hereditary properties. A graph property is hereditary if it is closed under taking induced subgraphs. Examples of hereditary properties include acyclicity, bipartiteness, planarity, and bounded (chromatic, independence) number, etc.
For each class of graphs 𝒢 satisfying a hereditary property (a hereditary graph-class), we propose a randomized algorithm which, with high probability, (1) accepts if the input graph G belongs to 𝒢, and (2) rejects if G contains at least |B| + 1 disjoint subgraphs not belonging to 𝒢. The round complexity of our algorithm is 𝒪(((log (|𝒢_n|))/n) +|B|) ⋅polylog(n)) , where 𝒢_n is the set of n-node graphs in 𝒢.
Finally, we obtain an impossibility result that proves that our result is tight. Indeed, we consider the hereditary class of acyclic graphs, and we prove that there is no algorithm that can distinguish between a graph being acyclic and a graph having |B| disjoint cycles.
Cite as
David Cifuentes-Núñez, Pedro Montealegre, and Ivan Rapaport. Recognizing Hereditary Properties in the Presence of Byzantine Nodes. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 26:1-26:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{cifuentesnunez_et_al:LIPIcs.OPODIS.2025.26,
author = {Cifuentes-N\'{u}\~{n}ez, David and Montealegre, Pedro and Rapaport, Ivan},
title = {{Recognizing Hereditary Properties in the Presence of Byzantine Nodes}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {26:1--26:15},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.26},
URN = {urn:nbn:de:0030-drops-251990},
doi = {10.4230/LIPIcs.OPODIS.2025.26},
annote = {Keywords: Byzantine protocols, congested clique, hereditary properties}
}
Document
Where to Place Your TEE? In Search of a Censorship-Resilient Design for Rollup Sequencers
Abstract
Ethereum is the dominant blockchain ecosystem capable of executing Turing-complete smart contracts. Rollups gained significant traction as the primary layer 2 (L2) solution meant to bring horizontal scalability to the main Ethereum network (L1). A core component of any rollup is the sequencer, which creates new L2 blocks to be submitted in rollup batches to L1. In most of the current rollup architectures, this component is centralised. As a result, these designs are prone to inconspicuous censorship practices by the sequencer. Trusted execution environments (TEEs) can guarantee the integrity of various sequencer components, which is instrumental in addressing censorship. However, the reaction of the system design to censorship attempts depends on where a TEE is integrated and which components it protects. In particular, this reaction is limited in the case of a monolithic TEE-protected sequencer design. Proposer-Builder Separation (PBS) is a non-monolithic paradigm adopted on L1, which separates the production of blocks from proposing them for inclusion in the blockchain. Recently, PBS has been considered for integration with L2 sequencers, with an impact on alleviating censorship. In this paper, we explore the design space of TEE-integrating PBS and non-PBS sequencer variants. First, we introduce a formal framework for the censorship actions that captures the specificity of the L2 sequencer. Then, we analyse to what extent the different designs address these censorship actions. Our main contribution is a novel design variation that allows for a precise observation of censored transactions. In the presence of TEEs, in a PBS setting, we demonstrate this precise observability, which is necessary to enable resilience to censorship.
Cite as
Andrei Arusoaie, Claudiu-Nicu Bărbieru, Oana-Otilia Captarencu, Pascal Felber, Corentin Libert, Emanuel Onica, Etienne Rivière, Valerio Schiavoni, and Peterson Yuhala. Where to Place Your TEE? In Search of a Censorship-Resilient Design for Rollup Sequencers. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 27:1-27:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{arusoaie_et_al:LIPIcs.OPODIS.2025.27,
author = {Arusoaie, Andrei and B\u{a}rbieru, Claudiu-Nicu and Captarencu, Oana-Otilia and Felber, Pascal and Libert, Corentin and Onica, Emanuel and Rivi\`{e}re, Etienne and Schiavoni, Valerio and Yuhala, Peterson},
title = {{Where to Place Your TEE? In Search of a Censorship-Resilient Design for Rollup Sequencers}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {27:1--27:20},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.27},
URN = {urn:nbn:de:0030-drops-252000},
doi = {10.4230/LIPIcs.OPODIS.2025.27},
annote = {Keywords: Rollups, Trusted Execution Environments, Censorship}
}
Document
Demand-Aware Small-World Networks on Clustered Demands
Abstract
Small-world networks are attractive for the efficient routing they provide, requiring only a low link density. They have hence also been considered for the design of distributed systems, such as peer-to-peer networks. However, existing small-world network designs are oblivious to the actual traffic they serve. In this paper, we initiate the study of demand-aware small-world networks. In particular, we extend the Kleinberg graph model, by allowing the nodes to choose the distribution of long-range links according to the traffic demand. We present a formal analysis of the weighted route lengths for the important case of clustered demands. We show both in theory and in simulations, using real-world traffic workloads, that demand-aware small-world graphs can significantly outperform their demand-oblivious counterparts.
Cite as
Chen Avin, Robert Elsässer, Aleksander Figiel, Darya Melnyk, and Stefan Schmid. Demand-Aware Small-World Networks on Clustered Demands. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 28:1-28:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{avin_et_al:LIPIcs.OPODIS.2025.28,
author = {Avin, Chen and Els\"{a}sser, Robert and Figiel, Aleksander and Melnyk, Darya and Schmid, Stefan},
title = {{Demand-Aware Small-World Networks on Clustered Demands}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {28:1--28:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.28},
URN = {urn:nbn:de:0030-drops-252017},
doi = {10.4230/LIPIcs.OPODIS.2025.28},
annote = {Keywords: Small-world networks, demand-aware network designs, algorithms and analysis, clustering}
}
Document
How Exhaustive Does an Extension-Based Proof Need to Be?
Abstract
The class of extension-based proofs encompasses traditional valency arguments. It has been shown that they are insufficient to establish the impossibility of (n-1)-set agreement among n ≥ 3 processes in an asynchronous system with crash failures. We generalize this definition to k-exhaustive extension-based proofs, in which a prover can learn the maximum length of all executions involving a set of at most k processes from a specified configuration (which may be infinite). An upper bound on the length of these executions enables the prover to determine the outputs of all these executions. When k = n, this enables the prover to perform an exhaustive search of all reachable configurations, so it knows everything about the protocol. On the other hand, extension based proofs are as powerful as 1-exhaustive extension-based proofs. For any task with no deterministic, wait-free solution among n ≥ 2 processes, we show that there is an (n-1)-exhaustive extension-based proof of its impossibility. This is done using a new characterization of such tasks. In contrast, we prove that for 1 ≤ k ≤ n-2, there is no k-exhaustive extension-based proof of the impossibility of (n-1)-set agreement.
Cite as
Faith Ellen, Shihao Liu, Leqi Zhu, Eli Gafni, and Rati Gelashvili. How Exhaustive Does an Extension-Based Proof Need to Be?. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 29:1-29:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{ellen_et_al:LIPIcs.OPODIS.2025.29,
author = {Ellen, Faith and Liu, Shihao and Zhu, Leqi and Gafni, Eli and Gelashvili, Rati},
title = {{How Exhaustive Does an Extension-Based Proof Need to Be?}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {29:1--29:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.29},
URN = {urn:nbn:de:0030-drops-252020},
doi = {10.4230/LIPIcs.OPODIS.2025.29},
annote = {Keywords: Extension-based proof, set agreement, valency argument, zero-one exclusion}
}
Document
Byzantine-Tolerant Phase Clock
Abstract
A phase clock is a basic synchronization mechanism that keeps distributed nodes closely synchronized to execute the same phase of a distributed algorithm. A phase clock is typically implemented with a local logical counter that keeps track of the current phase count. Phase clocks are particularly useful in population protocols for implementing leader election and majority selection. We study phase clocks that tolerate Byzantine faults. We show that there is a phase clock that tolerates up to f < n/3 faulty nodes, where n is the number of nodes, such that the gap of the local counter values is O(n²log n). The gap can be further lowered to O(log n) when f ≤ n/8. We also show that if f > n/3, then the gap grows to infinity as time increases. While analyzing phase clock we introduce novel techniques and bounds for balls into bins processes, which might be of independent interest. Using the phase clock, we obtain a majority selection population protocol that tolerates up to f faults and decides on the majority value in O(log² n) parallel time using poly-log states per node.
Cite as
Costas Busch, Paweł Garncarek, and Dariusz R. Kowalski. Byzantine-Tolerant Phase Clock. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 30:1-30:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{busch_et_al:LIPIcs.OPODIS.2025.30,
author = {Busch, Costas and Garncarek, Pawe{\l} and Kowalski, Dariusz R.},
title = {{Byzantine-Tolerant Phase Clock}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {30:1--30:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.30},
URN = {urn:nbn:de:0030-drops-252036},
doi = {10.4230/LIPIcs.OPODIS.2025.30},
annote = {Keywords: phase clock, Byzantine nodes, population protocols, balls into bins}
}
Document
Fast Re-Routing in Networks: On the Complexity of Perfect Resilience
Abstract
To achieve fast recovery from link failures, most modern communication networks feature fully decentralized fast re-routing mechanisms. These re-routing mechanisms rely on pre-installed static re-routing rules at the nodes (the routers), which depend only on local failure information, namely on the failed links incident to the node. Ideally, a network is perfectly resilient: the re-routing rules ensure that packets are always successfully routed to their destinations as long as the source and the destination are still physically connected in the underlying network after the failures. Unfortunately, there are examples where achieving perfect resilience is not possible. Surprisingly, only very little is known about the algorithmic aspect of when and how perfect resilience can be achieved.
We investigate the computational complexity of analyzing such local fast re-routing mechanisms. Our main result is a negative one: we show that even checking whether a given set of static re-routing rules ensures perfect resilience is coNP-complete. Additionally, we investigate other fundamental variations of the problem. In particular, we show that our coNP-completeness proof also applies to scenarios where the re-routing rules have specific patterns (known as skipping in the literature).
On the positive side, for scenarios where nodes do not have information about the link from which a packet arrived (the so-called in-port), we present a linear-time algorithm to realize perfect resilience whenever possible (which we show can also be determined in linear time).
Cite as
Matthias Bentert, Esra Ceylan, Valentin Hübner, Stefan Schmid, and Jiří Srba. Fast Re-Routing in Networks: On the Complexity of Perfect Resilience. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 31:1-31:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{bentert_et_al:LIPIcs.OPODIS.2025.31,
author = {Bentert, Matthias and Ceylan, Esra and H\"{u}bner, Valentin and Schmid, Stefan and Srba, Ji\v{r}{\'\i}},
title = {{Fast Re-Routing in Networks: On the Complexity of Perfect Resilience}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {31:1--31:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.31},
URN = {urn:nbn:de:0030-drops-252040},
doi = {10.4230/LIPIcs.OPODIS.2025.31},
annote = {Keywords: routing in computer networks, fast re-route, perfect resilience, complexity}
}
Document
Recolorable Graph Exploration by an Oblivious Agent with Fewer Colors
Abstract
Recently, Böckenhauer, Frei, Unger, and Wehner (SIROCCO 2023) introduced a novel variant of the graph exploration problem in which a single memoryless agent must visit all nodes of an unknown, undirected, and connected graph before returning to its starting node. Unlike the standard model for mobile agents, edges are not labeled with port numbers. Instead, the agent can color its current node and observe the color of each neighboring node. To move, it specifies a target color and then moves to an adversarially chosen neighbor of that color. They analyzed the minimum number of colors required for successful exploration and proposed an elegant algorithm that enables the agent to explore an arbitrary graph using only eight colors. In this paper, we present a novel graph exploration algorithm that requires only six colors. Furthermore, we prove that five colors are sufficient if we consider only a restricted class of graphs, which we call the φ-free graphs, a class that includes every graph with maximum degree at most three and every cactus.
Cite as
Shota Takahashi, Haruki Kanaya, Shoma Hiraoka, Ryota Eguchi, and Yuichi Sudo. Recolorable Graph Exploration by an Oblivious Agent with Fewer Colors. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 32:1-32:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{takahashi_et_al:LIPIcs.OPODIS.2025.32,
author = {Takahashi, Shota and Kanaya, Haruki and Hiraoka, Shoma and Eguchi, Ryota and Sudo, Yuichi},
title = {{Recolorable Graph Exploration by an Oblivious Agent with Fewer Colors}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {32:1--32:15},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.32},
URN = {urn:nbn:de:0030-drops-252052},
doi = {10.4230/LIPIcs.OPODIS.2025.32},
annote = {Keywords: mobile agents, recolorable graphs, graph exploration}
}
Document
Resolving Conflicts with Grace: Dynamically Concurrent Universality
Abstract
Synchronization is the major obstacle to scalability in distributed computing. Concurrent operations on the shared data engage in synchronization when they encounter a conflict, i.e., their effects depend on the order in which they are applied. Ideally, one would like to detect conflicts in a dynamic manner, i.e., adjusting to the current system state. Indeed, it is very common that two concurrent operations conflict only in some rarely occurring states. In this paper, we define the notion of dynamic concurrency: an operation employs strong synchronization primitives only if it has to arbitrate with concurrent operations, given the current system state. We then present a dynamically concurrent universal construction.
Cite as
Petr Kuznetsov and Nathan Josia Schrodt. Resolving Conflicts with Grace: Dynamically Concurrent Universality. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 33:1-33:29, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{kuznetsov_et_al:LIPIcs.OPODIS.2025.33,
author = {Kuznetsov, Petr and Schrodt, Nathan Josia},
title = {{Resolving Conflicts with Grace: Dynamically Concurrent Universality}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {33:1--33:29},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.33},
URN = {urn:nbn:de:0030-drops-252068},
doi = {10.4230/LIPIcs.OPODIS.2025.33},
annote = {Keywords: Universal Construction, Consensus, Dynamic Concurrency}
}
Document
Uniform Deployment of Mobile Robots in Complete Bipartite Graphs
Abstract
In this paper, we address the problem of uniformly deploying mobile robots in complete bipartite graphs. Specifically, when n robots are positioned arbitrarily at distinct nodes in a complete bipartite graph K_{n,n}, which consists of two n-node sets V_L and V_R, the uniform deployment problem requires the robots to achieve one of the following configurations: (a) each node in V_L is occupied by exactly one robot, with no robots in V_R, or (b) each node in V_R is occupied by exactly one robot, with no robots in V_L. In either configuration, the distance between any two robots is 2, ensuring that the robots are uniformly deployed. In this paper, we explore the relationship between the visibility range of robots and the solvability of the uniform deployment problem. First, we characterize solvable and unsolvable initial configurations under the assumption that robots have an infinite visibility range. Next, we demonstrate that visibility range 1 (meaning robots can only observe nodes at a distance of 1 and the robots positioned on them) is insufficient, proving the impossibility of solving the problem under this constraint. Conversely, we show that visibility range Θ(log n) is sufficient by presenting an algorithm that solves the uniform deployment problem in O(1) rounds, starting from any solvable initial configuration. Finally, we briefly introduce an example showing that robots with a constant visibility range (which is 3 in this example) cannot solve the problem in a native way.
Cite as
Masahiro Shibata, Naoki Kitamura, Ryota Eguchi, Yuichi Sudo, Junya Nakamura, Yonghwan Kim, Yoshiaki Katayama, Toshimitsu Masuzawa, Quentin Bramas, and Sébastien Tixeuil. Uniform Deployment of Mobile Robots in Complete Bipartite Graphs. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 34:1-34:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{shibata_et_al:LIPIcs.OPODIS.2025.34,
author = {Shibata, Masahiro and Kitamura, Naoki and Eguchi, Ryota and Sudo, Yuichi and Nakamura, Junya and Kim, Yonghwan and Katayama, Yoshiaki and Masuzawa, Toshimitsu and Bramas, Quentin and Tixeuil, S\'{e}bastien},
title = {{Uniform Deployment of Mobile Robots in Complete Bipartite Graphs}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {34:1--34:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.34},
URN = {urn:nbn:de:0030-drops-252075},
doi = {10.4230/LIPIcs.OPODIS.2025.34},
annote = {Keywords: mobile robots, uniform deployment, complete bipartite graphs}
}
Document
Morpheus Consensus: Excelling on Trails and Autobahns
Abstract
Recent research in consensus has often focussed on protocols for State-Machine-Replication (SMR) that can handle high throughputs. Such state-of-the-art protocols (generally DAG-based) induce undue overhead when the needed throughput is low, or else exhibit unnecessarily-poor latency and communication complexity during periods of low throughput.
Here we present Morpheus Consensus, which naturally morphs from a quiescent low-throughput leaderless blockchain protocol to a high-throughput leader-based DAG protocol and back, excelling in latency and complexity in both settings. During high-throughout, Morpheus pars with state-of-the-art DAG-based protocols, including Autobahn [Giridharan et al., 2024]. During low-throughput, Morpheus exhibits competitive complexity and lower latency than standard protocols such as PBFT [Castro et al., 1999] and Tendermint [Buchman, 2016; Buchman et al., 2018], which in turn do not perform well during high-throughput.
The key idea of Morpheus is that as long as blocks do not conflict (due to Byzantine behaviour, network delays, or high-throughput simultaneous production) it produces a forkless blockchain, promptly finalizing each block upon arrival. It assigns a leader only if one is needed to resolve conflicts, in a manner and with performance not unlike Autobahn.
Cite as
Andrew Lewis-Pye and Ehud Shapiro. Morpheus Consensus: Excelling on Trails and Autobahns. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 35:1-35:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{lewispye_et_al:LIPIcs.OPODIS.2025.35,
author = {Lewis-Pye, Andrew and Shapiro, Ehud},
title = {{Morpheus Consensus: Excelling on Trails and Autobahns}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {35:1--35:20},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.35},
URN = {urn:nbn:de:0030-drops-252086},
doi = {10.4230/LIPIcs.OPODIS.2025.35},
annote = {Keywords: Distributed computing, consensus, quiescence}
}
Document
BlindPerm: Efficient MEV Mitigation with an Encrypted Mempool and Permutation
Abstract
Maximal Extractable Value (MEV) is a crucial challenge in blockchains and cryptocurrencies. A principal countermeasure is using encrypted mempools to hide the transaction payloads until they are committed in a block. However, the existing approaches based on encrypted mempools remain vulnerable to metadata leakage and may not provide sufficient mitigation against block producers due to their sole control in block preparation. In this paper, we propose techniques that utilize randomized permutation on the committed block, offering a multi-layer solution. With a focus on proof-of-stake (PoS) committee-based consensus, we then introduce BlindPerm, a framework that enhances an encrypted mempool with permutation and present various optimizations. Notably, we propose a construction where this enhancement comes at essentially no overhead by piggybacking on the encrypted mempool and without relying on any external entity such as randomness beacon. Further, we illustrate the effectiveness of our solutions by running simulations using historical Ethereum data.
Cite as
Alireza Kavousi, Duc V. Le, Philipp Jovanovic, and George Danezis. BlindPerm: Efficient MEV Mitigation with an Encrypted Mempool and Permutation. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 36:1-36:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{kavousi_et_al:LIPIcs.OPODIS.2025.36,
author = {Kavousi, Alireza and Le, Duc V. and Jovanovic, Philipp and Danezis, George},
title = {{BlindPerm: Efficient MEV Mitigation with an Encrypted Mempool and Permutation}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {36:1--36:21},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael 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/LIPIcs.OPODIS.2025.36},
URN = {urn:nbn:de:0030-drops-252091},
doi = {10.4230/LIPIcs.OPODIS.2025.36},
annote = {Keywords: Encrypted mempool, maximal extractable value, distributed systems}
}