Volume
LIPIcs, Volume 356
39th International Symposium on Distributed Computing (DISC 2025)
-
Part of:
Series:
Leibniz International Proceedings in Informatics (LIPIcs)
Conference: International Symposium on Distributed Computing (DISC)
Event
DISC 2025, October 27-31, 2025, Berlin, GermanyEditor
Publication Details
- published at: 2025-10-22
- Publisher: Schloss Dagstuhl – Leibniz-Zentrum für Informatik
- ISBN: 978-3-95977-402-4
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Document
Complete Volume
LIPIcs, Volume 356, DISC 2025, Complete Volume
Abstract
LIPIcs, Volume 356, DISC 2025, Complete Volume
Cite as
39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 1-1144, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@Proceedings{kowalski:LIPIcs.DISC.2025,
title = {{LIPIcs, Volume 356, DISC 2025, Complete Volume}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {1--1144},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025},
URN = {urn:nbn:de:0030-drops-249682},
doi = {10.4230/LIPIcs.DISC.2025},
annote = {Keywords: LIPIcs, Volume 356, DISC 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
39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 0:i-0:xxii, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{kowalski:LIPIcs.DISC.2025.0,
author = {Kowalski, Dariusz R.},
title = {{Front Matter, Table of Contents, Preface, Conference Organization}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {0:i--0:xxii},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.0},
URN = {urn:nbn:de:0030-drops-249676},
doi = {10.4230/LIPIcs.DISC.2025.0},
annote = {Keywords: Front Matter, Table of Contents, Preface, Conference Organization}
}
Document
ABEL: Perfect Asynchronous Byzantine Extension from List-Decoding
Abstract
Asynchronous byzantine agreement extension studies the message complexity of L-bit multivalued asynchronous byzantine agreement given access to a binary asynchronous Byzantine agreement protocol.
We prove that asynchronous byzantine agreement extension can be solved with perfect security and optimal resilience in O(nL+n² log n) total communication (in bits) in addition to a single call to a binary asynchronous Byzantine agreement protocol. For L = O(n log n), this gives an asymptotically optimal protocol, resolving a question that remained open for nearly two decades.
List decoding is a fundamental concept in theoretical computer science and cryptography, enabling error correction beyond the unique decoding radius and playing a critical role in constructing robust codes, hardness amplification, and secure cryptographic protocols. A key novelty of our perfectly secure and optimally resilient asynchronous byzantine agreement extension protocol is that it uses list decoding - making a striking new connection between list decoding and asynchronous Byzantine agreement.
Cite as
Ittai Abraham and Gilad Asharov. ABEL: Perfect Asynchronous Byzantine Extension from List-Decoding. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 1:1-1:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{abraham_et_al:LIPIcs.DISC.2025.1,
author = {Abraham, Ittai and Asharov, Gilad},
title = {{ABEL: Perfect Asynchronous Byzantine Extension from List-Decoding}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {1:1--1:20},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.1},
URN = {urn:nbn:de:0030-drops-248185},
doi = {10.4230/LIPIcs.DISC.2025.1},
annote = {Keywords: Asynchronous Byzantine Agreement, Perfect Security}
}
Document
On the Efficiency of Dynamic Transaction Scheduling in Blockchain Sharding
Abstract
Sharding is a technique to speed up transaction processing in blockchains, where the n processing nodes in the blockchain are divided into s disjoint groups (shards) that can process transactions in parallel. We study dynamic scheduling problems on a shard graph G_s where transactions arrive online over time and are not known in advance. Each transaction may access at most k shards, and we denote by d the worst distance between a transaction and its accessing (destination) shards (the parameter d is unknown to the shards). To handle different values of d, we assume a locality sensitive decomposition of G_s into clusters of shards, where every cluster has a leader shard that schedules transactions for the cluster. We first examine the simpler case of the stateless model, where leaders are not aware of the current state of the transaction accounts, and we prove a O(d log² s ⋅ min{k, √s}) competitive ratio for latency. We then consider the stateful model, where leader shards gather the current state of accounts, and we prove a O(log s⋅ min{k, √s}+log² s) competitive ratio for latency. Each leader calculates the schedule in polynomial time for each transaction that it processes. We show that for any ε > 0, approximating the optimal schedule within a (min{k, √s})^{1 -ε} factor is NP-hard. Hence, our bound for the stateful model is within a poly-log factor from the best possibly achievable. To the best of our knowledge, this is the first work to establish provably efficient dynamic scheduling algorithms for blockchain sharding systems.
Cite as
Ramesh Adhikari, Costas Busch, and Miroslav Popovic. On the Efficiency of Dynamic Transaction Scheduling in Blockchain Sharding. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 2:1-2:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{adhikari_et_al:LIPIcs.DISC.2025.2,
author = {Adhikari, Ramesh and Busch, Costas and Popovic, Miroslav},
title = {{On the Efficiency of Dynamic Transaction Scheduling in Blockchain Sharding}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {2:1--2:23},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.2},
URN = {urn:nbn:de:0030-drops-248191},
doi = {10.4230/LIPIcs.DISC.2025.2},
annote = {Keywords: Blockchain, Blockchain Sharding, Dynamic Transaction Scheduling}
}
Document
An Almost-Logarithmic Lower Bound for Leader Election with Bounded Value Contention
Abstract
We investigate the step complexity of the Leader Election problem (and implementing the corresponding test-and-set object) in asynchronous shared memory, where processes communicate through registers supporting atomic read and write and must coordinate so that a single process becomes the leader. Determining tight step complexity bounds for solving this problem is one of the key open problems in the theory of shared memory distributed computing. The best known algorithm is a randomized tournament-tree, which has worst-case expected step complexity O(log N) for N processes. There are provably no deterministic wait-free algorithms, and only restricted lower bounds are known for obstruction-free and randomized wait-free algorithms. We introduce a new lower bound that establishes an Ω((log N)/(log log N + log Q)) step complexity for any obstruction-free Leader Election algorithm, where N is the number of processes, and 2 ≤ Q ≤ N is a bound on the value contention, which we define as the maximum number of different values that processes can be simultaneously poised to write to the same register in any execution of the algorithm. Our result is strictly stronger than previous bounds based on write contention. In particular, it implies new lower bounds on step complexity that depend on register size.
Cite as
Dan Alistarh, Faith Ellen, and Alexander Fedorov. An Almost-Logarithmic Lower Bound for Leader Election with Bounded Value Contention. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 3:1-3:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{alistarh_et_al:LIPIcs.DISC.2025.3,
author = {Alistarh, Dan and Ellen, Faith and Fedorov, Alexander},
title = {{An Almost-Logarithmic Lower Bound for Leader Election with Bounded Value Contention}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {3:1--3:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.3},
URN = {urn:nbn:de:0030-drops-248204},
doi = {10.4230/LIPIcs.DISC.2025.3},
annote = {Keywords: Leader Election, Test-and-Set, Shared Memory, Lower Bounds}
}
Document
pod: An Optimal-Latency, Censorship-Free, and Accountable Generalized Consensus Layer
Abstract
This work addresses the inherent issues of high latency in blockchains and low scalability in traditional consensus protocols. We present pod, a novel notion of consensus whose first priority is to achieve the physically-optimal latency of 2δ, or one round-trip, i.e., requiring only one network trip (duration δ) for writing a transaction and one for reading it.
To accomplish this, we first eliminate inter-replica communication. Instead, clients send transactions directly to all replicas, which independently process transactions and append them to local logs. Replicas assign a timestamp and a sequence number to each transaction in their logs, allowing clients to extract valuable metadata about the transactions and the system state. Later on, clients retrieve these logs and extract transactions (and associated metadata) from them.
Necessarily, this construction achieves weaker properties than a total-order broadcast protocol, due to existing lower bounds. Our work models the primitive of pod and defines its security properties. We then show pod-core, a protocol that satisfies properties such as transaction confirmation within 2δ, censorship resistance against Byzantine replicas, and accountability for safety violations. We show that single-shot auctions can be realized using the pod notion and observe that it is also sufficient for other popular applications.
Cite as
Orestis Alpos, Bernardo David, Jakov Mitrovski, Odysseas Sofikitis, and Dionysis Zindros. pod: An Optimal-Latency, Censorship-Free, and Accountable Generalized Consensus Layer. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 4:1-4:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{alpos_et_al:LIPIcs.DISC.2025.4,
author = {Alpos, Orestis and David, Bernardo and Mitrovski, Jakov and Sofikitis, Odysseas and Zindros, Dionysis},
title = {{pod: An Optimal-Latency, Censorship-Free, and Accountable Generalized Consensus Layer}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {4:1--4:24},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.4},
URN = {urn:nbn:de:0030-drops-248219},
doi = {10.4230/LIPIcs.DISC.2025.4},
annote = {Keywords: consensus, censorship resistance, accountability, auctions}
}
Document
DAG It Off: Latency Prefers No Common Coins
Abstract
We introduce Black Marlin, the first Directed Acyclic Graph (DAG)-based Byzantine atomic broadcast protocol in a partially synchronous setting that successfully forgoes the reliable broadcast and common coin primitives. Black Marlin achieves the optimal latency of 3 rounds of communication (4.25 with Byzantine faults) while maintaining optimal communication and amortized communication complexities. We present a formal security analysis of the protocol, accompanied by empirical evidence that Black Marlin outperforms state-of-the-art DAG-based protocols in both throughput and latency.
Cite as
Ignacio Amores-Sesar, Viktor Grøndal, Adam Holmgård, and Mads Ottendal. DAG It Off: Latency Prefers No Common Coins. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 5:1-5:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{amoressesar_et_al:LIPIcs.DISC.2025.5,
author = {Amores-Sesar, Ignacio and Gr{\o}ndal, Viktor and Holmg\r{a}rd, Adam and Ottendal, Mads},
title = {{DAG It Off: Latency Prefers No Common Coins}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {5:1--5:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.5},
URN = {urn:nbn:de:0030-drops-248221},
doi = {10.4230/LIPIcs.DISC.2025.5},
annote = {Keywords: Atomic broadcast, DAG-based, Partial synchrony}
}
Document
Hierarchical Consensus: Scalability Through Optimism and Weak Liveness
Abstract
Scalability is a central concern of Byzantine Fault Tolerant (BFT) distributed protocols. The ubiquitous approach to work around the well-known Dolev-Reischuk Ω(n²) communication complexity lower bound is to use a random selection process to draw a hopefully small committee from a population of agents to run the communication-heavy protocol. We propose a notion of hierarchical consensus that combines two sub-protocols: an optimistic primary sub-protocol that can tolerate less than 1/2 failures and a fallback secondary protocol that can tolerate less than 1/3 failures; we achieve the higher failure threshold by requiring a weaker notion of liveness for the primary. This distinction between the level of fault tolerance between primary and secondary is reflected in the size of committees implementing these protocols. For a population of agents with close to 2/3 of honest agents, we need to select a committee with hundreds of agents to reach the level of tolerance expected for the primary, whereas we need thousands to reach the level expected for the secondary with a very small probability of error ε. Our hierarchical construct is such that if the primary comes to a decision, it can simply propagate it to the secondary protocol, so it does not need to properly engage in an agreement protocol independently. Our architecture is flexible and allows us to use our technique for most protocols that are based on random sampling. By studying hierarchical protocols, we discovered new theoretical results of independent interest. Specifically, the ability to handover from a primary protocol requires a new Justifiability property that allows agents to pre-decide on a value, such that if the protocol decides, it must be on that pre-decided value.
Cite as
Pedro Antonino, Antoine Durand, and A. W. Roscoe. Hierarchical Consensus: Scalability Through Optimism and Weak Liveness. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 6:1-6:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{antonino_et_al:LIPIcs.DISC.2025.6,
author = {Antonino, Pedro and Durand, Antoine and Roscoe, A. W.},
title = {{Hierarchical Consensus: Scalability Through Optimism and Weak Liveness}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {6:1--6:20},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.6},
URN = {urn:nbn:de:0030-drops-248232},
doi = {10.4230/LIPIcs.DISC.2025.6},
annote = {Keywords: Hierarchical, Handover, Justifiability, Consensus, Distributed Systems, Blockchain}
}
Document
On the Shape Containment Problem Within the Amoebot Model with Reconfigurable Circuits
Abstract
In programmable matter, we consider a large number of tiny, primitive computational entities called particles that run distributed algorithms to control global properties of the particle structure. Shape formation problems, where the particles have to reorganize themselves into a desired shape using basic movement abilities, are particularly interesting. In the related shape containment problem, the particles are given the description of a shape S and have to find maximally scaled representations of S within the initial configuration, without movements. For example, if S is a triangle, they have to identify the largest subsets of particles that already form a triangle. While the shape formation problem is being studied extensively, no attention has been given to the shape containment problem, which may have additional uses besides shape formation, such as detecting structural flaws.
In this paper, we consider the shape containment problem within the geometric amoebot model for programmable matter, using its reconfigurable circuit extension to enable the instantaneous transmission of primitive signals on connected subsets of particles. We first prove a lower runtime bound of Ω (√n) synchronous rounds for the general problem, where n is the number of particles. Then, we present simple and efficient primitives for identifying subsets that form the desired shape. Using these primitives, we construct a large class of shapes which we call snowflakes. This class contains, among others, all shapes composed of parallelograms and hexagons, and the class of star convex shapes. Let k be the maximum scale of the considered shape in a given amoebot structure. If the shape is star convex, we solve it within 𝒪 (log² k) rounds. If it is a snowflake but not star convex, we solve it within 𝒪 (√n log n) rounds.
Cite as
Matthias Artmann, Andreas Padalkin, and Christian Scheideler. On the Shape Containment Problem Within the Amoebot Model with Reconfigurable Circuits. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 7:1-7:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{artmann_et_al:LIPIcs.DISC.2025.7,
author = {Artmann, Matthias and Padalkin, Andreas and Scheideler, Christian},
title = {{On the Shape Containment Problem Within the Amoebot Model with Reconfigurable Circuits}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {7:1--7:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.7},
URN = {urn:nbn:de:0030-drops-248240},
doi = {10.4230/LIPIcs.DISC.2025.7},
annote = {Keywords: Programmable matter, amoebot model, reconfigurable circuits, shape containment}
}
Document
Auditable Shared Objects: From Registers to Synchronization Primitives
Abstract
Auditability allows to track operations performed on a shared object, recording who accessed which information. This gives data owners more control on their data. Initially studied in the context of single-writer registers, this work extends the notion of auditability to other shared objects, and studies their properties.
We start by moving from single-writer to multi-writer registers, and provide an implementation of an auditable n-writer m-reader read / write register, with O(n+m) step complexity. This implementation uses (m+n)-sliding registers, which have consensus number m+n. We show that this consensus number is necessary. The implementation extends naturally to support an auditable load-linked / store-conditional (LL/SC) shared object. LL/SC is a primitive that supports efficient implementation of many shared objects. Finally, we relate auditable registers to other access control objects, by implementing an anti-flickering deny list from auditable registers.
Cite as
Hagit Attiya, Antonio Fernández Anta, Alessia Milani, Alexandre Rapetti, and Corentin Travers. Auditable Shared Objects: From Registers to Synchronization Primitives. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 8:1-8:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{attiya_et_al:LIPIcs.DISC.2025.8,
author = {Attiya, Hagit and Anta, Antonio Fern\'{a}ndez and Milani, Alessia and Rapetti, Alexandre and Travers, Corentin},
title = {{Auditable Shared Objects: From Registers to Synchronization Primitives}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {8:1--8:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.8},
URN = {urn:nbn:de:0030-drops-248253},
doi = {10.4230/LIPIcs.DISC.2025.8},
annote = {Keywords: Auditability, Wait-free implementation, Synchronization power, Distributed objects, Shared memory, LL/SC, Deny List}
}
Document
Distributed Download from an External Data Source in Byzantine Majority Settings
Abstract
We consider the Download problem in the Data Retrieval Model, introduced in DISC'24, where a distributed set of peers, some of which may be Byzantine, seek to learn n bits of data stored at a trustworthy external data source. Each bit of data can be learned by a peer either through a direct and costly query of the source or through other peers that have already learned it; the goal is to design a collaborative protocol that reduces the query complexity defined as the maximum number of bits queried by any honest peer.
We begin with a randomized protocol for the Download problem that achieves optimal query complexity, up to a logarithmic factor. For a stronger "dynamic" adversary that can change the set of Byzantine peers from one round to the next, we achieve optimality (within log factors) for both query complexity (in expectation) and time complexity, but with larger messages. In broadcast communication, where all peers (including Byzantine peers) are required to send the same message to all peers, we achieve (up to log factors) an optimal trade-off between query complexity, time complexity, and message size with the dynamic adversary. All of our protocols can tolerate any constant fraction β < 1 of Byzantine peers.
Cite as
John Augustine, Soumyottam Chatterjee, Valerie King, Manish Kumar, Shachar Meir, and David Peleg. Distributed Download from an External Data Source in Byzantine Majority Settings. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 9:1-9:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{augustine_et_al:LIPIcs.DISC.2025.9,
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 Byzantine Majority Settings}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {9:1--9:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.9},
URN = {urn:nbn:de:0030-drops-248262},
doi = {10.4230/LIPIcs.DISC.2025.9},
annote = {Keywords: Byzantine Fault Tolerance, Blockchain Oracle, Data Retrieval Model, Distributed Download}
}
Document
Amnesiac Flooding: Easy to Break, Hard to Escape
Abstract
Broadcast is a central problem in distributed computing. Recently, Hussak and Trehan [PODC'19/ STACS'20/DC'23] proposed a stateless broadcasting protocol (Amnesiac Flooding), which was surprisingly proven to terminate in asymptotically optimal time (linear in the diameter of the network). However, it remains unclear: (i) Are there other stateless terminating broadcast algorithms with the desirable properties of Amnesiac Flooding, (ii) How robust is Amnesiac Flooding with respect to faults?
In this paper we make progress on both of these fronts. Under a reasonable restriction (obliviousness to message content) additional to the fault-free synchronous model, we prove that Amnesiac Flooding is the only strictly stateless deterministic protocol that can achieve terminating broadcast. We achieve this by identifying four natural properties of a terminating broadcast protocol that Amnesiac Flooding uniquely satisfies. In contrast, we prove that even minor relaxations of any of these four criteria allow the construction of other terminating broadcast protocols.
On the other hand, we prove that Amnesiac Flooding can become non-terminating or non-broadcasting, even if we allow just one node to drop a single message on a single edge in a single round. As a tool for proving this, we focus on the set of all configurations of transmissions between nodes in the network, and obtain a dichotomy characterizing the configurations, starting from which, Amnesiac Flooding terminates. Additionally, we characterise the structure of sets of Byzantine agents capable of forcing non-termination or non-broadcast of the protocol on arbitrary networks.
Cite as
Henry Austin, Maximilien Gadouleau, George B. Mertzios, and Amitabh Trehan. Amnesiac Flooding: Easy to Break, Hard to Escape. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 10:1-10:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{austin_et_al:LIPIcs.DISC.2025.10,
author = {Austin, Henry and Gadouleau, Maximilien and Mertzios, George B. and Trehan, Amitabh},
title = {{Amnesiac Flooding: Easy to Break, Hard to Escape}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {10:1--10:23},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.10},
URN = {urn:nbn:de:0030-drops-248273},
doi = {10.4230/LIPIcs.DISC.2025.10},
annote = {Keywords: Amnesiac flooding, Terminating protocol, Algorithm state, Stateless protocol, Flooding algorithm, Network algorithms, Graph theory, Termination, Communication, Broadcast}
}
Document
New Limits on Distributed Quantum Advantage: Dequantizing Linear Programs
Abstract
In this work, we give two results that put new limits on distributed quantum advantage in the context of the LOCAL model of distributed computing:
1) We show that there is no distributed quantum advantage for any linear program. Put otherwise, if there is a quantum-LOCAL algorithm 𝒜 that finds an α-approximation of some linear optimization problem Π in T communication rounds, we can construct a classical, deterministic LOCAL algorithm 𝒜' that finds an α-approximation of Π in T rounds. As a corollary, all classical lower bounds for linear programs, including the KMW bound, hold verbatim in quantum-LOCAL.
2) Using the above result, we show that there exists a locally checkable labeling problem (LCL) for which quantum-LOCAL is strictly weaker than the classical deterministic SLOCAL model. Our results extend from quantum-LOCAL to finitely dependent and non-signaling distributions, and one of the corollaries of our work is that the non-signaling model and the SLOCAL model are incomparable in the context of LCL problems: By prior work, there exists an LCL problem for which SLOCAL is strictly weaker than the non-signaling model, and our work provides a separation in the opposite direction.
Cite as
Alkida Balliu, Corinna Coupette, Antonio Cruciani, Francesco d'Amore, Massimo Equi, Henrik Lievonen, Augusto Modanese, Dennis Olivetti, and Jukka Suomela. New Limits on Distributed Quantum Advantage: Dequantizing Linear Programs. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 11:1-11:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{balliu_et_al:LIPIcs.DISC.2025.11,
author = {Balliu, Alkida and Coupette, Corinna and Cruciani, Antonio and d'Amore, Francesco and Equi, Massimo and Lievonen, Henrik and Modanese, Augusto and Olivetti, Dennis and Suomela, Jukka},
title = {{New Limits on Distributed Quantum Advantage: Dequantizing Linear Programs}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {11:1--11:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.11},
URN = {urn:nbn:de:0030-drops-248280},
doi = {10.4230/LIPIcs.DISC.2025.11},
annote = {Keywords: linear programming, distributed quantum advantage, quantum-LOCAL model, SLOCAL model, online-LOCAL model, non-signaling distributions, locally checkable labeling problems, dequantization}
}
Document
Distributed Computation with Local Advice
Abstract
Algorithms with advice have received ample attention in the distributed and online settings, and they have recently proven useful also in dynamic settings. In this work we study local computation with advice: the goal is to solve a graph problem Π with a distributed algorithm in T(Δ) communication rounds, for some function T that only depends on the maximum degree Δ of the graph, and the key question is how many bits of advice per node are needed.
Some of our results regard Locally Checkable Labeling problems (LCLs), which is an important family of problems that includes various coloring and orientation problems on finite-degree graphs. These are constraint-satisfaction graph problems that can be defined with a finite set of valid input/output-labeled neighborhoods.
Our main results are:
1) Any locally checkable labeling problem can be solved with only 1 bit of advice per node in graphs with sub-exponential growth (the number of nodes within radius r is sub-exponential in r; for example, grids are such graphs). Moreover, we can make the set of nodes that carry advice bits arbitrarily sparse. As a corollary, any locally checkable labeling problem admits a locally checkable proof with 1 bit per node in graphs with sub-exponential growth.
2) The assumption of sub-exponential growth is complemented by a conditional lower bound: assuming the Exponential-Time Hypothesis, there are locally checkable labeling problems that cannot be solved in general with any constant number of bits per node.
3) In any graph we can find an almost-balanced orientation (indegrees and outdegrees differ by at most one) with 1 bit of advice per node, and again we can make the advice arbitrarily sparse. As a corollary, we can also compress an arbitrary subset of edges so that a node of degree d stores only d/2 + 2 bits, and we can decompress it locally, in T(Δ) rounds.
4) In any graph of maximum degree Δ, we can find a Δ-coloring (if it exists) with 1 bit of advice per node, and again, we can make the advice arbitrarily sparse.
5) In any 3-colorable graph, we can find a 3-coloring with 1 bit of advice per node. As a corollary, in bounded-degree graphs there is a locally checkable proof that certifies 3-colorability with 1 bit of advice per node, while prior work shows that this is not possible with a proof labeling scheme (PLS), which is a more restricted setting where the verifier can only see up to distance 1. Our work shows that for many problems the key threshold is not whether we can achieve 1 bit of advice per node, but whether we can make the advice arbitrarily sparse. To formalize this idea, we develop a general framework of composable schemas that enables us to build algorithms for local computation with advice in a modular fashion: once we have (1) a schema for solving Π₁ and (2) a schema for solving Π₂ assuming an oracle for Π₁, we can also compose them and obtain (3) a schema that solves Π₂ without the oracle. It turns out that many natural problems admit composable schemas, all of them can be solved with only 1 bit of advice, and we can make the advice arbitrarily sparse.
Cite as
Alkida Balliu, Sebastian Brandt, Fabian Kuhn, Krzysztof Nowicki, Dennis Olivetti, Eva Rotenberg, and Jukka Suomela. Distributed Computation with Local Advice. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 12:1-12:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{balliu_et_al:LIPIcs.DISC.2025.12,
author = {Balliu, Alkida and Brandt, Sebastian and Kuhn, Fabian and Nowicki, Krzysztof and Olivetti, Dennis and Rotenberg, Eva and Suomela, Jukka},
title = {{Distributed Computation with Local Advice}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {12:1--12:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.12},
URN = {urn:nbn:de:0030-drops-248295},
doi = {10.4230/LIPIcs.DISC.2025.12},
annote = {Keywords: Distributed graph algorithms, LOCAL model, computation with advice, locally checkable labeling problems, proof labeling schemes, locally checkable proofs, graph coloring, exponential-time hypothesis}
}
Document
Towards Fully Automatic Distributed Lower Bounds
Abstract
In the past few years, a successful line of research has led to lower bounds for several fundamental local graph problems in the distributed setting. These results were obtained via a technique called round elimination. On a high level, the round elimination technique can be seen as a recursive application of a function that takes as input a problem Π and outputs a problem Π' that is one round easier than Π. Applying this function recursively to concrete problems of interest can be highly nontrivial, which is one of the reasons that has made the technique difficult to approach. The contribution of our paper is threefold.
Firstly, we develop a new and fully automatic method for finding so-called fixed point relaxations under round elimination. The detection of a non-0-round solvable fixed point relaxation of a problem Π immediately implies lower bounds of Ω(log_Δ n) and Ω(log_Δ log n) rounds for deterministic and randomized algorithms for Π, respectively.
Secondly, we show that this automatic method is indeed useful, by obtaining lower bounds for defective coloring problems. More precisely, as an application of our procedure, we show that the problem of coloring the nodes of a graph with 3 colors and defect at most (Δ - 3)/2 requires Ω(log_Δ n) rounds for deterministic algorithms and Ω(log_Δ log n) rounds for randomized ones. Additionally, we provide a simplified proof for an existing defective coloring lower bound. We note that lower bounds for coloring problems are notoriously challenging to obtain, both in general, and via the round elimination technique.
{Both the first and (indirectly) the second contribution build on our third contribution: a new method to compute the one-round easier problem Π' in the round elimination framework. This method heavily simplifies the usage of the round elimination technique, and in fact it has been successfully exploited in a recent work in order to prove quantum advantage in the distributed setting [STOC '25].}
Cite as
Alkida Balliu, Sebastian Brandt, Fabian Kuhn, Dennis Olivetti, and Joonatan Saarhelo. Towards Fully Automatic Distributed Lower Bounds. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 13:1-13:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{balliu_et_al:LIPIcs.DISC.2025.13,
author = {Balliu, Alkida and Brandt, Sebastian and Kuhn, Fabian and Olivetti, Dennis and Saarhelo, Joonatan},
title = {{Towards Fully Automatic Distributed Lower Bounds}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {13:1--13:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.13},
URN = {urn:nbn:de:0030-drops-248308},
doi = {10.4230/LIPIcs.DISC.2025.13},
annote = {Keywords: round elimination, lower bounds, defective coloring}
}
Document
Energy-Efficient Maximal Independent Sets in Radio Networks
Abstract
The maximal independent set (MIS) is one of the most fundamental problems in distributed computing, and it has been studied intensively for over four decades. This paper focuses on the MIS problem in the radio network model, a standard model widely used to model wireless networks, particularly ad hoc wireless and sensor networks. Energy is a premium resource in these networks, which are typically battery-powered. Hence, designing distributed algorithms that use as little energy as possible is crucial. We use the well-established energy model where a node can be sleeping or awake in a round, and only the awake rounds (when it can send or listen) determine the energy complexity of the algorithm, which we want to minimize.
We present new, more energy-efficient MIS algorithms in radio networks with arbitrary and unknown graph topology. We present algorithms for two popular variants of the radio model - with collision detection (CD) and without collision detection (no-CD). Specifically, we obtain the following results:
1) CD model: We present a randomized distributed MIS algorithm with energy complexity O(log n), round complexity O(log² n), and failure probability 1 / poly(n), where n is the network size. We show that our energy complexity is optimal by showing a matching Ω(log n) lower bound.
2) no-CD model: In the more challenging no-CD model, we present a randomized distributed MIS algorithm with energy complexity O(log²n log log n), round complexity O(log³ n log Δ), and failure probability 1 / poly(n). The energy complexity of our algorithm is significantly lower than the round (and energy) complexity of O(log³ n) of the best known distributed MIS algorithm of Davies [PODC 2023] for arbitrary graph topology.
Cite as
Dominick Banasik, Varsha Dani, Fabien Dufoulon, Aayush Gupta, Thomas P. Hayes, and Gopal Pandurangan. Energy-Efficient Maximal Independent Sets in Radio Networks. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 14:1-14:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{banasik_et_al:LIPIcs.DISC.2025.14,
author = {Banasik, Dominick and Dani, Varsha and Dufoulon, Fabien and Gupta, Aayush and Hayes, Thomas P. and Pandurangan, Gopal},
title = {{Energy-Efficient Maximal Independent Sets in Radio Networks}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {14:1--14:24},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.14},
URN = {urn:nbn:de:0030-drops-248311},
doi = {10.4230/LIPIcs.DISC.2025.14},
annote = {Keywords: Distributed Computing, Energy Complexity, Sleeping Model, Radio Networks, Maximal Independent Set}
}
Document
Asynchronous Latency and Fast Atomic Snapshot
Abstract
This paper introduces a novel, fast atomic-snapshot protocol for asynchronous message-passing systems. In the process of defining what "fast" means exactly, we spot a few interesting issues that arise when conventional time metrics are applied to long-lived asynchronous algorithms. We reveal some gaps in latency claims made in earlier work on snapshot algorithms, which hamper their comparative time-complexity analysis. We then come up with a new unifying time-complexity metric that captures the latency of an operation in an asynchronous, long-lived implementation. This allows us to formally grasp latency improvements of our atomic-snapshot algorithm with respect to the state-of-the-art protocols: optimal latency in fault-free runs without contention, short constant latency in fault-free runs with contention, the worst-case latency proportional to the number of active concurrent failures, and constant amortized latency.
Cite as
João Paulo Bezerra, Luciano Freitas, Petr Kuznetsov, and Matthieu Rambaud. Asynchronous Latency and Fast Atomic Snapshot. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 15:1-15:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{bezerra_et_al:LIPIcs.DISC.2025.15,
author = {Bezerra, Jo\~{a}o Paulo and Freitas, Luciano and Kuznetsov, Petr and Rambaud, Matthieu},
title = {{Asynchronous Latency and Fast Atomic Snapshot}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {15:1--15:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.15},
URN = {urn:nbn:de:0030-drops-248326},
doi = {10.4230/LIPIcs.DISC.2025.15},
annote = {Keywords: Asynchronous systems, time complexity, atomic snapshot, crash faults}
}
Document
Perpetual Exploration in Anonymous Synchronous Networks with a Byzantine Black Hole
Abstract
In this paper, we investigate the following question:
"How can a group of initially co-located mobile agents perpetually explore an unknown graph, when one stationary node occasionally behaves maliciously, under the control of an adversary?"
This malicious node is termed as "Byzantine black hole (BBH)" and at any given round it may choose to destroy all visiting agents, or none of them. While investigating this question, we found out that this subtle power turns out to drastically undermine even basic exploration strategies which have been proposed in the context of a classical, always active, black hole.
We study this perpetual exploration problem in the presence of at most one BBH, without initial knowledge of the network size. Since the underlying graph may be 1-connected, perpetual exploration of the entire graph may be infeasible. Accordingly, we define two variants of the problem, termed as PerpExploration-BBH and PerpExploration-BBH-Home. In the former, the agents are tasked to perform perpetual exploration of at least one component, obtained after the exclusion of the BBH. In the latter, the agents are tasked to perform perpetual exploration of the component which contains the home node, where agents are initially co-located. Naturally, PerpExploration-BBH-Home is a special case of PerpExploration-BBH. The mobile agents are controlled by a synchronous scheduler, and they communicate via face-to-face model of communication.
The main objective in this paper is to determine the minimum number of agents necessary and sufficient to solve these problems. We first consider the problems in acyclic networks, and we obtain optimal algorithms that solve PerpExploration-BBH with 4 agents, and PerpExploration-BBH-Home with 6 agents in trees. The lower bounds hold even in path graphs. In general graphs, we give a non-trivial lower bound of 2Δ-1 agents for PerpExploration-BBH, and an upper bound of 3Δ+3 agents for PerpExploration-BBH-Home. To the best of our knowledge, this is the first paper that studies a variant of a black hole in arbitrary networks, without initial topological knowledge about the network.
Cite as
Adri Bhattacharya, Pritam Goswami, Evangelos Bampas, and Partha Sarathi Mandal. Perpetual Exploration in Anonymous Synchronous Networks with a Byzantine Black Hole. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 16:1-16:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{bhattacharya_et_al:LIPIcs.DISC.2025.16,
author = {Bhattacharya, Adri and Goswami, Pritam and Bampas, Evangelos and Mandal, Partha Sarathi},
title = {{Perpetual Exploration in Anonymous Synchronous Networks with a Byzantine Black Hole}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {16:1--16:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.16},
URN = {urn:nbn:de:0030-drops-248333},
doi = {10.4230/LIPIcs.DISC.2025.16},
annote = {Keywords: mobile agents, perpetual exploration, malicious host, Byzantine black hole}
}
Document
Deterministic Synchronous Self-Stabilizing BFS Construction with Constant Space Complexity
Abstract
In this paper, we resolve a long-standing open problem in self-stabilization asking whether it is possible to construct a spanning tree using constant memory per node in a synchronous semi-uniform networks, i.e., networks in which one node is distinguished. We design a synchronous self-stabilizing algorithm that constructs a breadth-first search (BFS) tree in any anonymous semi-uniform network using only a constant number of bits of memory per node. Crucially, our approach operates without any prior knowledge of global network parameters such as maximum degree, diameter, or number of nodes. In contrast to traditional self-stabilizing methods - such as pointer-to-neighbors, distance-to-root, or identifiers - that are unsuitable under strict memory constraints, our solution employs an innovative constant-space token dissemination mechanism. This mechanism effectively eliminates cycles and rectifies errors in the BFS structure, ensuring both correctness and memory efficiency. The proposed algorithm not only meets the stringent requirements of memory-constrained distributed systems, but also opens new avenues for research in the design of self-stabilizing protocols under severe resource limitations: constant space-complexity may not systematically prevent the existence of self-stabilizing algorithms for important non-trivial tasks.
Cite as
Lélia Blin, Franck Petit, and Sébastien Tixeuil. Deterministic Synchronous Self-Stabilizing BFS Construction with Constant Space Complexity. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 17:1-17:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{blin_et_al:LIPIcs.DISC.2025.17,
author = {Blin, L\'{e}lia and Petit, Franck and Tixeuil, S\'{e}bastien},
title = {{Deterministic Synchronous Self-Stabilizing BFS Construction with Constant Space Complexity}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {17:1--17:15},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.17},
URN = {urn:nbn:de:0030-drops-248349},
doi = {10.4230/LIPIcs.DISC.2025.17},
annote = {Keywords: Distributed algorithms, fault-tolerance, transient faults, self-stabilization, memory optimization}
}
Document
Complexity Landscape for Local Certification
Abstract
An impressive recent line of work has charted the complexity landscape of distributed graph algorithms. For many settings, it has been determined which time complexities exist, and which do not (in the sense that no local problem could have an optimal algorithm with that complexity). In this paper, we initiate the study of the landscape for space complexity of distributed graph algorithms. More precisely, we focus on the local certification setting, where a prover assigns certificates to nodes to certify a property, and where the space complexity is measured by the size of the certificates.
Already for anonymous paths and cycles, we unveil a surprising landscape:
- There is a gap between complexity O(1) and Θ(log log n) in paths. This is the first gap established in local certification.
- There exists a property that has complexity Θ(log log n) in paths, a regime that was not known to exist for a natural property.
- There is a gap between complexity O(1) and Θ(log n) in cycles, hence a gap that is exponentially larger than for paths.
We then generalize our result for paths to the class of trees. Namely, we show that there is a gap between complexity O(1) and Θ(log log d) in trees, where d is the diameter. We finally describe some settings where there are no gaps at all.
To prove our results we develop a new toolkit, based on various results of automata theory and arithmetic, which is of independent interest.
Cite as
Nicolas Bousquet, Laurent Feuilloley, and Sébastien Zeitoun. Complexity Landscape for Local Certification. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 18:1-18:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{bousquet_et_al:LIPIcs.DISC.2025.18,
author = {Bousquet, Nicolas and Feuilloley, Laurent and Zeitoun, S\'{e}bastien},
title = {{Complexity Landscape for Local Certification}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {18:1--18:21},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.18},
URN = {urn:nbn:de:0030-drops-248350},
doi = {10.4230/LIPIcs.DISC.2025.18},
annote = {Keywords: Local certification, proof-labeling schemes, locally checkable proofs, space complexity, distributed graph algorithms, complexity gap}
}
Document
Robust Predicate and Function Computation in Continuous Chemical Reaction Networks
Abstract
We initiate the study of "rate-constant-independent" computation of Boolean predicates (decision problems) and numerical functions in the continuous model of chemical reaction networks (CRNs), which model the amount of a chemical species as a nonnegative, real-valued concentration, representing an average count per unit volume. Real-valued numerical functions have previously been studied [Chen et al., 2023], finding that exactly the continuous, piecewise rational linear (meaning linear with rational slopes) functions f: ℝ_{>0}^k → ℝ_{>0} can be computed stably (a.k.a., rate-independently), meaning roughly that the CRN gets the answer correct no matter the rate at which reactions occur. For example the reactions X₁ → Y and X₂+Y → ∅, starting with inputs X₁ ≥ X₂, converge to output Y having concentration equal to the initial difference of inputs X₁ - X₂, no matter the relative rate at which each reaction proceeds.
We first show that, contrary to the case of real-valued functions, continuous CRNs are severely limited in the Boolean predicates they can stably decide, reporting a yes/no answer based only on which inputs are 0 or positive, but not on the exact positive value of any input.
This limitation motivates a slightly relaxed notion of rate-independent computation in CRNs that we call robust computation. The standard mass-action rate model is used, in which each reaction (e.g., A+B →^k C) is assigned a rate (A ⋅ B ⋅ k in this example) equal to the product of its reactant concentrations and its rate constant k. We say the computation is correct in this model if it converges to the correct output for any positive choice of rate constants. This adversary is weaker than the adversary defining stable computation, the latter being able to run reactions at rates that are not those of mass-action for any choice of rate constants (e.g., the stable adversary may deactivate a reaction temporarily, even if all reactants are positive).
We show that CRNs can robustly decide every predicate that is a finite Boolean combination of threshold predicates, where a threshold predicate is defined by taking a rational weighted sum of the inputs x ∈ ℝ^k_{≥ 0} and comparing to a constant, answering the question "Is ∑_{i = 1}^k w_i ⋅ x(i) > h?", for rational weights w_i and real threshold h. Turning to function computation, we show that CRNs can robustly compute any piecewise affine function with rational coefficients, where threshold predicates determine which affine piece to evaluate for a given input x.
Cite as
Kim Calabrese, David Doty, and Mina Latifi. Robust Predicate and Function Computation in Continuous Chemical Reaction Networks. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 19:1-19:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{calabrese_et_al:LIPIcs.DISC.2025.19,
author = {Calabrese, Kim and Doty, David and Latifi, Mina},
title = {{Robust Predicate and Function Computation in Continuous Chemical Reaction Networks}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {19:1--19:23},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.19},
URN = {urn:nbn:de:0030-drops-248368},
doi = {10.4230/LIPIcs.DISC.2025.19},
annote = {Keywords: chemical reaction networks, analog computation, mean-field limit}
}
Document
Two for One, One for All: Deterministic LDC-Based Robust Computation in Congested Clique
Abstract
We design a deterministic compiler that makes any computation in the Congested Clique model robust to a constant fraction α < 1 of adversarial crash faults. In particular, we show how a network of n nodes can compute any circuit of depth d, width ω, and gate total fan Δ, in d ⋅ ⌈ω/n² + Δ/n⌉ ⋅ 2^{O(√{log{n}}log log{n})} rounds in such a faulty model. As a corollary, any T-round Congested Clique algorithm can be compiled into an algorithm that completes in T² n^{o(1)} rounds in this model.
Our compiler obtains resilience to node crashes by coding information across the network, and its main underlying observation is that we can leverage locally-decodable codes (LDCs) to maintain a low complexity overhead, as these allow recovering the information needed at each computational step by querying only small parts of the codeword, instead of retrieving the entire coded message, which is inherent when using block codes.
The main technical contribution is that because erasures occur in known locations, which correspond to crashed nodes, we can derandomize classical LDC constructions by deterministically selecting query sets that avoid sufficiently many erasures. Moreover, when decoding multiple codewords in parallel, our derandomization load-balances the queries per-node, thereby preventing congestion and maintaining a low round complexity.
Deterministic decoding of LDCs presents a new challenge: the adversary can target precisely the (few) nodes that are queried for decoding a certain codeword. We overcome this issue via an adaptive doubling strategy: if a decoding attempt for a codeword fails, the node doubles the number of its decoding attempts. We employ a similar doubling technique when the adversary crashes the decoding node itself, replacing it dynamically with two other non-crashed nodes. By carefully combining these two doubling processes, we overcome the challenges posed by the combination of a deterministic LDC with a worst case pattern of crashes.
Cite as
Keren Censor-Hillel, Orr Fischer, Ran Gelles, and Pedro Soto. Two for One, One for All: Deterministic LDC-Based Robust Computation in Congested Clique. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 20:1-20:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{censorhillel_et_al:LIPIcs.DISC.2025.20,
author = {Censor-Hillel, Keren and Fischer, Orr and Gelles, Ran and Soto, Pedro},
title = {{Two for One, One for All: Deterministic LDC-Based Robust Computation in Congested Clique}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {20:1--20:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.20},
URN = {urn:nbn:de:0030-drops-248379},
doi = {10.4230/LIPIcs.DISC.2025.20},
annote = {Keywords: Congested Clique, Fault Tolerance, Error Correction Codes}
}
Document
Content-Oblivious Leader Election in 2-Edge-Connected Networks
Abstract
Censor-Hillel, Cohen, Gelles, and Sela (PODC 2022 & Distributed Computing 2023) studied fully-defective asynchronous networks, where communication channels may arbitrarily corrupt messages. The model is equivalent to content-oblivious computation, where nodes communicate solely via pulses. They showed that if the network is 2-edge-connected, then any algorithm for a noiseless setting can be simulated in the fully-defective setting; otherwise, no non-trivial computation is possible in the fully-defective setting. However, their simulation requires a predesignated leader, which they conjectured to be necessary for any non-trivial content-oblivious task.
Recently, Frei, Gelles, Ghazy, and Nolin (DISC 2024) refuted this conjecture for the special case of oriented ring topology. They designed two asynchronous content-oblivious leader election algorithms with message complexity O(n ⋅ ID_{max}), where n is the number of nodes and ID_{max} is the maximum ID. The first algorithm stabilizes in unoriented rings without termination detection. The second algorithm quiescently terminates in oriented rings, thus enabling the execution of the simulation algorithm after leader election. In this work, we present two results:
General 2-edge-connected topologies: First, we show an asynchronous content-oblivious leader election algorithm that quiescently terminates in any 2-edge-connected network with message complexity O(m ⋅ N ⋅ ID_{min}), where m is the number of edges, N is a known upper bound on the number of nodes, and ID_{min} is the smallest ID. Combined with the above simulation, this result shows that whenever a size bound N is known, any noiseless algorithm can be simulated in the fully-defective model without a preselected leader, fully refuting the conjecture.
Unoriented rings: We then show that the knowledge of N can be dropped in unoriented ring topologies by presenting a quiescently terminating election algorithm with message complexity O(n ⋅ ID_{max}) that matches the previous bound. Consequently, this result constitutes a strict improvement over the previous state of the art and shows that, on rings, fully-defective and noiseless communication are computationally equivalent, with no additional assumptions.
Cite as
Jérémie Chalopin, Yi-Jun Chang, Lyuting Chen, Giuseppe A. Di Luna, and Haoran Zhou. Content-Oblivious Leader Election in 2-Edge-Connected Networks. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 21:1-21:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{chalopin_et_al:LIPIcs.DISC.2025.21,
author = {Chalopin, J\'{e}r\'{e}mie and Chang, Yi-Jun and Chen, Lyuting and Di Luna, Giuseppe A. and Zhou, Haoran},
title = {{Content-Oblivious Leader Election in 2-Edge-Connected Networks}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {21:1--21:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.21},
URN = {urn:nbn:de:0030-drops-248385},
doi = {10.4230/LIPIcs.DISC.2025.21},
annote = {Keywords: Asynchronous model, fault tolerance, quiescent termination}
}
Document
The Complexity Landscape of Dynamic Distributed Subgraph Finding
Abstract
Bonne and Censor-Hillel (ICALP 2019) initiated the study of distributed subgraph finding in dynamic networks of limited bandwidth. For the case where the target subgraph is a clique, they determined the tight bandwidth complexity bounds in nearly all settings. However, several open questions remain, and very little is known about finding subgraphs beyond cliques. In this work, we consider these questions and explore subgraphs beyond cliques in the deterministic setting.
For finding cliques, we establish an Ω(log log n) bandwidth lower bound for one-round membership-detection under edge insertions only and an Ω(log log log n) bandwidth lower bound for one-round detection under both edge insertions and node insertions. Moreover, we demonstrate new algorithms to show that our lower bounds are tight in bounded-degree networks when the target subgraph is a triangle. Prior to our work, no lower bounds were known for these problems.
For finding subgraphs beyond cliques, we present a complete characterization of the bandwidth complexity of the membership-listing problem for every target subgraph, every number of rounds, and every type of topological change: node insertions, node deletions, edge insertions, and edge deletions. We also show partial characterizations for one-round membership-detection and listing.
Cite as
Yi-Jun Chang, Lyuting Chen, Yanyu Chen, Gopinath Mishra, and Mingyang Yang. The Complexity Landscape of Dynamic Distributed Subgraph Finding. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 22:1-22:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{chang_et_al:LIPIcs.DISC.2025.22,
author = {Chang, Yi-Jun and Chen, Lyuting and Chen, Yanyu and Mishra, Gopinath and Yang, Mingyang},
title = {{The Complexity Landscape of Dynamic Distributed Subgraph Finding}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {22:1--22:20},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.22},
URN = {urn:nbn:de:0030-drops-248399},
doi = {10.4230/LIPIcs.DISC.2025.22},
annote = {Keywords: Distributed algorithms, dynamic algorithms, subgraph finding}
}
Document
Boosting Payment Channel Network Liquidity with Topology Optimization and Transaction Selection
Abstract
Payment channel networks (PCNs) are a promising technology that alleviates blockchain scalability by shifting the transaction load from the blockchain to the PCN. Nevertheless, the network topology has to be carefully designed to maximise the transaction throughput in PCNs. Additionally, users in PCNs also have to make optimal decisions on which transactions to forward and which to reject to prolong the lifetime of their channels. In this work, we consider an input sequence of transactions over p parties. Each transaction consists of a transaction size, source, and target, and can be either accepted or rejected (entailing a cost). The goal is to design a PCN topology among the p cooperating parties, along with the channel capacities, and then output a decision for each transaction in the sequence to minimise the cost of creating and augmenting channels, as well as the cost of rejecting transactions. Our main contribution is an 𝒪(p) approximation algorithm for the problem with p parties. We further show that with some assumptions on the distribution of transactions, we can reduce the approximation ratio to 𝒪(√p). We complement our theoretical analysis with an empirical study of our assumptions and approach in the context of the Lightning Network.
Cite as
Krishnendu Chatterjee, Jan Matyáš Křišťan, Stefan Schmid, Jakub Svoboda, and Michelle Yeo. Boosting Payment Channel Network Liquidity with Topology Optimization and Transaction Selection. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 23:1-23:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{chatterjee_et_al:LIPIcs.DISC.2025.23,
author = {Chatterjee, Krishnendu and K\v{r}i\v{s}\v{t}an, Jan Maty\'{a}\v{s} and Schmid, Stefan and Svoboda, Jakub and Yeo, Michelle},
title = {{Boosting Payment Channel Network Liquidity with Topology Optimization and Transaction Selection}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {23:1--23:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.23},
URN = {urn:nbn:de:0030-drops-248402},
doi = {10.4230/LIPIcs.DISC.2025.23},
annote = {Keywords: Blockchains, Cryptocurrencies, Payment Channel Networks, Throughput, Optimisation, Graph Algorithms, Approximation Algorithms}
}
Document
Validity in Network-Agnostic Byzantine Agreement
Abstract
Byzantine Agreement (BA) considers a setting of n parties, out of which up to t can exhibit byzantine (malicious) behavior. Honest parties must decide on a common value (agreement), which must belong to a set determined by the honest inputs (validity). Depending on the use case, this set can grow or shrink, leading to various possible desiderata collectively known as validity conditions. Varying the validity property requirement can affect the regime under which BA is solvable.
Our work investigates how the selected validity property impacts BA solvability in the network-agnostic model, where the network can either be synchronous with up to t_s byzantine parties or asynchronous with up to t_a ≤ t_s byzantine parties. We give necessary and sufficient conditions for a validity property to render BA solvable, both for the case with cryptographic setup and for the one without. This traces the precise boundary of solvability in the network-agnostic model for every validity property. Our proof of sufficiency provides a universal protocol, that achieves BA for a given validity property whenever the provided conditions are satisfied.
We note that, for any non-trivial validity property, the condition 2 ⋅ t_s + t_a < n is necessary for BA to be solvable, even with cryptographic setup. Specializing this claim to t_a = 0 gives that t < n / 2 is required whenever one expects a purely synchronous protocol to also work in an asynchronous network when there are no corruptions. This is especially surprising given that, for some validity properties, t < n is a sufficient condition without the last stipulation.
Cite as
Andrei Constantinescu, Marc Dufay, Diana Ghinea, and Roger Wattenhofer. Validity in Network-Agnostic Byzantine Agreement. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 24:1-24:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{constantinescu_et_al:LIPIcs.DISC.2025.24,
author = {Constantinescu, Andrei and Dufay, Marc and Ghinea, Diana and Wattenhofer, Roger},
title = {{Validity in Network-Agnostic Byzantine Agreement}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {24:1--24:23},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.24},
URN = {urn:nbn:de:0030-drops-248413},
doi = {10.4230/LIPIcs.DISC.2025.24},
annote = {Keywords: byzantine agreement, validity, network-agnostic protocols}
}
Document
Model-Agnostic Approximation of Constrained Forest Problems
Abstract
Constrained Forest Problems (CFPs) as introduced by Goemans and Williamson in 1995 capture a wide range of network design problems with edge subsets as solutions, such as Minimum Spanning Tree, Steiner Forest, and Point-to-Point Connection. While individual CFPs have been studied extensively in individual computational models, a unified approach to solving general CFPs in multiple computational models has been lacking. Against this background, we present the shell-decomposition algorithm, a model-agnostic meta-algorithm that efficiently computes a (2+ε)-approximation to CFPs for a broad class of forest functions. The shell-decomposition algorithm isolates the problem-specific hardness of individual CFPs in a single computational subroutine, breaking the remainder of the computation into fundamental tasks that are studied extensively in a wide range of computational models. In contrast to prior work, our framework is compatible with the use of approximate distances.
To demonstrate the power and flexibility of this result, we instantiate our algorithm for three fundamental, NP-hard CFPs (Steiner Forest, Point-to-Point Connection, and Facility Placement and Connection) in three different computational models (Congest, PRAM, and Multi-Pass Streaming). For constant ε, we obtain the following (2+ε)-approximations in the Congest model: [(1)]
1) For Steiner Forest specified via input components (SF-IC), where each node knows the identifier of one of k disjoint subsets of V (the input components), we achieve a deterministic (2+ε)-approximation in 𝒪̃(√n+D+k) rounds, where D is the hop diameter of the graph, significantly improving over the state of the art.
2) For Steiner Forest specified via symmetric connection requests (SF-SCR), where connection requests are issued to pairs of nodes u,v ∈ V, we leverage randomized equality testing to reduce the running time to 𝒪̃(√n+D), succeeding with high probability.
3) For Point-to-Point Connection, we provide a (2+ε)-approximation in 𝒪̃(√n+D) rounds.
4) For Facility Placement and Connection, a relative of non-metric Uncapacitated Facility Location, we obtain a (2+ε)-approximation in 𝒪̃(√n + D) rounds. We further show how to replace the √n+D term by the complexity of solving Partwise Aggregation, achieving (near-)universal optimality in any setting in which a solution to Partwise Aggregation in near-shortcut-quality time is known. Notably, all of our concrete results can be derived with relative ease once our model-agnostic meta-algorithm has been specified. This demonstrates the power of our modularization approach to algorithm design.
Cite as
Corinna Coupette, Alipasha Montaseri, and Christoph Lenzen. Model-Agnostic Approximation of Constrained Forest Problems. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 25:1-25:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{coupette_et_al:LIPIcs.DISC.2025.25,
author = {Coupette, Corinna and Montaseri, Alipasha and Lenzen, Christoph},
title = {{Model-Agnostic Approximation of Constrained Forest Problems}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {25:1--25:24},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.25},
URN = {urn:nbn:de:0030-drops-248420},
doi = {10.4230/LIPIcs.DISC.2025.25},
annote = {Keywords: Distributed Graph Algorithms, Model-Agnostic Algorithms, Steiner Forest}
}
Document
Towards Constant Time Multi-Call Rumor Spreading on Small-Set Expanders
Abstract
We study a multi-call variant of the classic PUSH&PULL rumor spreading process where nodes can contact k of their neighbors instead of a single one during both PUSH and PULL operations. We show that rumor spreading can be made faster at the cost of an increased amount of communication between the nodes. As a motivating example, consider the process on a complete graph of n nodes: while the standard PUSH&PULL protocol takes Θ(log n) rounds, we prove that our k-PUSH&PULL variant completes in Θ(log_{k} n) rounds, with high probability.
We generalize this result in an expansion-sensitive way, as has been done for the classic PUSH&PULL protocol for different notions of expansion, e.g., conductance and vertex expansion. We consider small-set vertex expanders, graphs in which every sufficiently small subset of nodes has a large neighborhood, ensuring strong local connectivity. In particular, when the expansion parameter satisfies ϕ > 1, these graphs have a diameter of o(log n), as opposed to other standard notions of expansion. Since the graph’s diameter is a lower bound on the number of rounds required for rumor spreading, this makes small-set expanders particularly well-suited for fast information dissemination. We prove that k-PUSH&PULL takes O(log_{ϕ} n ⋅ log_{k} n) rounds in these expanders, with high probability. We complement this with a simple lower bound of Ω(log_{ϕ} n+ log_{k} n) rounds.
Cite as
Emilio Cruciani, Sebastian Forster, and Tijn de Vos. Towards Constant Time Multi-Call Rumor Spreading on Small-Set Expanders. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 26:1-26:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{cruciani_et_al:LIPIcs.DISC.2025.26,
author = {Cruciani, Emilio and Forster, Sebastian and de Vos, Tijn},
title = {{Towards Constant Time Multi-Call Rumor Spreading on Small-Set Expanders}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {26:1--26:25},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.26},
URN = {urn:nbn:de:0030-drops-248434},
doi = {10.4230/LIPIcs.DISC.2025.26},
annote = {Keywords: small set expansion, vertex expansion, rumor spreading, multi-call rumor spreading, push\&pull protocol}
}
Document
On the h-Majority Dynamics with Many Opinions
Abstract
We present the first upper bound on the convergence time to consensus of the well-known h-majority dynamics with k opinions, in the synchronous setting, for h and k that are both non-constant values. We suppose that, at the beginning of the process, there is some initial additive bias towards some plurality opinion, that is, there is an opinion that is supported by x nodes while any other opinion is supported by strictly fewer nodes. We prove that, with high probability, if the bias is ω(√x) and the initial plurality opinion is supported by at least x = ω(log n) nodes, then the process converges to plurality consensus in O(log n) rounds whenever h = ω(n log n / x). A main corollary is the following: if k = o(n / log n) and the process starts from an almost-balanced configuration with an initial bias of magnitude ω(√{n/k}) towards the initial plurality opinion, then any function h = ω(k log n) suffices to guarantee convergence to consensus in O(log n) rounds, with high probability. Our upper bound shows that the lower bound of Ω(k / h²) rounds to reach consensus given by Becchetti et al. (2017) cannot be pushed further than Ω̃(k / h). Moreover, the bias we require is asymptotically smaller than the Ω(√{nlog n}) bias that guarantees plurality consensus in the 3-majority dynamics: in our case, the required bias is at most any (arbitrarily small) function in ω(√x) for any value of k ≥ 2.
Cite as
Francesco d'Amore, Niccolò D'Archivio, George Giakkoupis, and Emanuele Natale. On the h-Majority Dynamics with Many Opinions. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 27:1-27:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{damore_et_al:LIPIcs.DISC.2025.27,
author = {d'Amore, Francesco and D'Archivio, Niccol\`{o} and Giakkoupis, George and Natale, Emanuele},
title = {{On the h-Majority Dynamics with Many Opinions}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {27:1--27:24},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.27},
URN = {urn:nbn:de:0030-drops-248448},
doi = {10.4230/LIPIcs.DISC.2025.27},
annote = {Keywords: Distributed Algorithms, Randomized Algorithms, Markov Chains, Consensus Problem, Opinion dynamics, Plurality Consensus}
}
Document
Byzantine Consensus in the Random Asynchronous Model
Abstract
We propose a novel relaxation of the classic asynchronous network model, called the random asynchronous model, which removes adversarial message scheduling while preserving unbounded message delays and Byzantine faults. Instead of an adversary dictating message order, delivery follows a random schedule. We analyze Byzantine consensus at different resilience thresholds (n = 3f+1, n = 2f+1, and n = f+2) and show that our relaxation allows consensus with probabilistic guarantees which are impossible in the standard asynchronous model or even the partially synchronous model. We complement these protocols with corresponding impossibility results, establishing the limits of consensus in the random asynchronous model.
Cite as
George Danezis, Jovan Komatovic, Lefteris Kokoris-Kogias, Alberto Sonnino, and Igor Zablotchi. Byzantine Consensus in the Random Asynchronous Model. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 28:1-28:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{danezis_et_al:LIPIcs.DISC.2025.28,
author = {Danezis, George and Komatovic, Jovan and Kokoris-Kogias, Lefteris and Sonnino, Alberto and Zablotchi, Igor},
title = {{Byzantine Consensus in the Random Asynchronous Model}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {28:1--28:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.28},
URN = {urn:nbn:de:0030-drops-248457},
doi = {10.4230/LIPIcs.DISC.2025.28},
annote = {Keywords: network model, asynchronous, random scheduler, Byzantine consensus}
}
Document
Strong Linearizability Without Compare&Swap: The Case of Bags
Abstract
Because strongly-linearizable objects provide stronger guarantees than linearizability, they serve as valuable building blocks for the design of concurrent data structures. Yet, many objects that have linearizable implementations from base objects weaker than compare&swap objects do not have strongly-linearizable implementations from the same base objects. We focus on one such object: the bag, a multiset from which processes can take unspecified elements.
We present the first lock-free, strongly-linearizable implementation of a bag from interfering objects (specifically, registers and test&set objects). This may be surprising, since there are provably no such implementations of stacks or queues.
Since a bag can contain arbitrarily many elements, an unbounded amount of space must be used to implement it. Hence, it makes sense to also consider a bag with a bound on its capacity. However, like stacks and queues, a bag with capacity b shared by more than 2b processes has no lock-free, strongly-linearizable implementation from interfering objects. If we further restrict a bounded bag so that only one process can insert into it, we are able to obtain a lock-free, strongly-linearizable implementation from O(b+n) interfering objects, where n is the number of processes.
Our goal is to understand the circumstances under which strongly-linearizable implementations of bags exist and, more generally, to understand the power of interfering objects.
Cite as
Faith Ellen and Gal Sela. Strong Linearizability Without Compare&Swap: The Case of Bags. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 29:1-29:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{ellen_et_al:LIPIcs.DISC.2025.29,
author = {Ellen, Faith and Sela, Gal},
title = {{Strong Linearizability Without Compare\&Swap: The Case of Bags}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {29:1--29:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.29},
URN = {urn:nbn:de:0030-drops-248464},
doi = {10.4230/LIPIcs.DISC.2025.29},
annote = {Keywords: Strong-Linearizability, Bag, Concurrent Data Structures, Wait-Freedom, Lock-Freedom}
}
Document
Team Formation and Applications
Abstract
A novel long-lived distributed problem, called Team Formation (TF), is introduced together with a message- and time-efficient randomized algorithm. The problem is defined over the asynchronous model with a complete communication graph, using bounded size messages, where a certain fraction of the nodes may experience a generalized, strictly stronger, version of initial failures. The goal of a TF algorithm is to assemble tokens injected by the environment, in a distributed manner, into teams of size σ, where σ is a parameter of the problem.
The usefulness of TF is demonstrated by using it to derive efficient algorithms for many distributed problems. Specifically, we show that various (one-shot as well as long-lived) distributed problems reduce to TF. This includes well-known (and extensively studied) distributed problems such as several versions of leader election and threshold detection. For example, we are the first to break the linear message complexity bound for asynchronous implicit leader election. We also improve the time complexity of message-optimal algorithms for asynchronous explicit leader election. Other distributed problems that reduce to TF are new ones, including matching players in online gaming platforms, a generalization of gathering, constructing a perfect matching in an induced subgraph of the complete graph, and more. To complement our positive contribution, we establish a tight lower bound on the message complexity of TF algorithms.
Cite as
Yuval Emek, Shay Kutten, Ido Rafael, and Gadi Taubenfeld. Team Formation and Applications. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 30:1-30:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{emek_et_al:LIPIcs.DISC.2025.30,
author = {Emek, Yuval and Kutten, Shay and Rafael, Ido and Taubenfeld, Gadi},
title = {{Team Formation and Applications}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {30:1--30:25},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.30},
URN = {urn:nbn:de:0030-drops-248474},
doi = {10.4230/LIPIcs.DISC.2025.30},
annote = {Keywords: asynchronous message-passing, complete communication graph, initial failures, leader election, matching}
}
Document
Lower Bounds for k-Set Agreement in Fault-Prone Networks
Abstract
We develop a new lower bound for k-set agreement in synchronous message-passing systems connected by an arbitrary directed communication network, where up to t processes may crash. Our result thus generalizes the ⌊t/k⌋ + 1 lower bound for complete networks in the t-resilient model by Chaudhuri, Herlihy, Lynch, and Tuttle [JACM 2000]. Moreover, it generalizes two lower bounds for oblivious algorithms in synchronous systems connected by an arbitrary undirected communication network known to the processes, namely, the domination number-based lower bound by Castañeda, Fraigniaud, Paz, Rajsbaum, Roy, and Travers [TCS 2021] for failure-free processes, and the radius-based lower bound in the t-resilient model by Fraigniaud, Nguyen, and Paz [STACS 2024].
Our topological proof non-trivially generalizes and extends the connectivity-based approach for the complete network, as presented in the book by Herlihy, Kozlov, and Rajsbaum (2013). It is based on a sequence of shellable carrier maps that, starting from a shellable input complex, determine the evolution of the protocol complex: During the first ⌊t/k⌋ rounds, carrier maps that crash exactly k processes per round are used, which ensure high connectivity of their images. A Sperner’s lemma style argument can thus be used to prove that k-set agreement is still impossible by that round. From round ⌊t/k⌋ + 1 up to our actual lower bound, a novel carrier map is employed, which maintains high connectivity. As a by-product, our proof also provides a strikingly simple lower-bound for k-set agreement in synchronous systems with an arbitrary communication network, where exactly t ≥ 0 processes crash initially, i.e., before taking any step. We demonstrate that the resulting additional agreement overhead can be expressed via an appropriately defined radius of the communication graphs, and show that the usual input pseudosphere complex for k-set agreement can be replaced by an exponentially smaller input complex based on Kuhn triangulations, which we prove to be also shellable.
Cite as
Pierre Fraigniaud, Minh Hang Nguyen, Ami Paz, Ulrich Schmid, and Hugo Rincon-Galeana. Lower Bounds for k-Set Agreement in Fault-Prone Networks. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 31:1-31:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{fraigniaud_et_al:LIPIcs.DISC.2025.31,
author = {Fraigniaud, Pierre and Nguyen, Minh Hang and Paz, Ami and Schmid, Ulrich and Rincon-Galeana, Hugo},
title = {{Lower Bounds for k-Set Agreement in Fault-Prone Networks}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {31:1--31:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.31},
URN = {urn:nbn:de:0030-drops-248480},
doi = {10.4230/LIPIcs.DISC.2025.31},
annote = {Keywords: Distributed computing, k-set agreement, time complexity, lower bounds, topology}
}
Document
Coordination Through Stochastic Channels
Abstract
We consider a stochastic network model consisting of a set of n synchronous processes communicating by message passing. In each round, processes send messages directly to each other over a complete communication graph. The processes do not fail, but messages can be lost. Each message is delivered with probability p, for a given parameter p ∈ [0,1]. We study the following optimization version of approximate agreement in this model. We assume that processes start with binary input values, execute an algorithm for a fixed number of rounds, and decide values in [0,1] satisfying the usual validity requirement stating that if all processes start with the same input value, then they should all decide that value. We propose deterministic algorithms that minimize the expected discrepancy, namely, the expected maximum distance between the decided values. We also present lower bounds on the expected discrepancy, which demonstrate the optimality of our algorithms for two processes. Finally, we present applications of our algorithms to solve randomized consensus and randomized approximate agreement.
Cite as
Pierre Fraigniaud, Boaz Patt-Shamir, and Sergio Rajsbaum. Coordination Through Stochastic Channels. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 32:1-32:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{fraigniaud_et_al:LIPIcs.DISC.2025.32,
author = {Fraigniaud, Pierre and Patt-Shamir, Boaz and Rajsbaum, Sergio},
title = {{Coordination Through Stochastic Channels}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {32:1--32:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.32},
URN = {urn:nbn:de:0030-drops-248493},
doi = {10.4230/LIPIcs.DISC.2025.32},
annote = {Keywords: Approximate agreement, randomized consensus, stochastic models, topology}
}
Document
Approach of Agents with Restricted Fuel Tanks
Abstract
Two mobile agents, modelled as points in the plane moving at speed 1, have to get at a distance at most 1 from each other. This task is known as approach or rendezvous in the plane. An adversary initially places both agents at distinct points, called their bases, at distance at most D, and wakes them up at possibly different times. Each of the agents has a fuel tank that allows them to traverse a trajectory of length D, and can be replenished at the base of the agent. The algorithm of each agent consists of a series of actions which are either moves at a chosen distance in a chosen direction or staying idle for a chosen period of time. For a given instance of the approach task, the execution time of an approach algorithm is the length of the period between the start of the later agent and the moment of approach.
Our goal is to design approach algorithms with optimal time complexity. We consider two independent coherence assumptions. One of them is time coherence, i.e., agents start simultaneously, and the other is orientation coherence: agents have compatible compasses, showing the same North direction. Our main result is establishing optimal time complexity of the approach problem with restricted fuel tanks. It turns out that this optimal complexity heavily depends on the above coherence assumptions. If both of them are satisfied then approach can be performed in time O(D²) and we show that this complexity is optimal. If any of the two coherence assumptions is missing then approach can be performed in time O(D²√D) and we prove that this order of magnitude cannot be improved.
Our main technical contribution are lower bounds showing that, for each of the considered scenarios, our fairly natural approach algorithms are, in fact, optimal.
Cite as
Adam Ganczorz, Tomasz Jurdzinski, Andrzej Pelc, and Grzegorz Stachowiak. Approach of Agents with Restricted Fuel Tanks. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 33:1-33:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{ganczorz_et_al:LIPIcs.DISC.2025.33,
author = {Ganczorz, Adam and Jurdzinski, Tomasz and Pelc, Andrzej and Stachowiak, Grzegorz},
title = {{Approach of Agents with Restricted Fuel Tanks}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {33:1--33:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.33},
URN = {urn:nbn:de:0030-drops-248506},
doi = {10.4230/LIPIcs.DISC.2025.33},
annote = {Keywords: mobile agent, approach, rendezvous, plane, restricted energy}
}
Document
New Distributed Interactive Proofs for Planarity: A Matter of Left and Right
Abstract
We provide new distributed interactive proofs (DIP) for planarity and related graph families. The notion of a distributed interactive proof (DIP) was introduced by Kol, Oshman, and Saxena (PODC 2018). In this setting, the verifier consists of n nodes connected by a communication graph G. The prover is a single entity that communicates with all nodes by short messages. The goal is to verify that the graph G satisfies a certain property (e.g., planarity) in a small number of rounds, and with a small communication bound, denoted as the proof size.
Prior work by Naor, Parter and Yogev (SODA 2020) presented a DIP for planarity that uses three interaction rounds and a proof size of O(log n). Feuilloley et al. (PODC 2020) showed that the same can be achieved with a single interaction round and without randomization, by providing a proof labeling scheme with a proof size of O(log n). In a subsequent work, Bousquet, Feuilloley, and Pierron (OPODIS 2021) achieved the same bound for related graph families such as outerplanarity, series-parallel graphs, and graphs of treewidth at most 2. In this work, we design new DIPs that use exponentially shorter proofs compared to the state-of-the-art bounds. Our main results are:
- There is a 5-round protocol with O(log log n) proof size for outerplanarity.
- There is a 5-round protocol with O(log log n) proof size for verifying embedded planarity and O(log log n+log Δ) proof size for general planar graphs, where Δ is the maximum degree in the graph. In the former setting, it is assumed that an embedding of the graph is given (e.g., each node holds a clockwise orientation of its neighbors) and the goal is to verify that it is a valid planar embedding. The latter result should be compared with the non-interactive setting for which there is lower bound of Ω(log n) bits for graphs with Δ = O(1) by Feuilloley et al. (PODC 2020).
- The non-interactive deterministic lower bound of Ω(log n) bits by Feuilloley et al. (PODC 2020) can be extended to hold even if the verifier is randomized. Moreover, the lower bound holds even with the assumption that the verifier’s randomness comes in the form of an unbounded random string shared among the nodes. We also show that our DIPs can be extended to protocols with similar bounds for verifying series-parallel graphs and graphs with tree-width at most 2. Perhaps surprisingly, our results demonstrate that the key technical barrier for obtaining o(log log n) labels for all our problems is a basic sorting verification task in which all nodes are embedded on an oriented path P ⊆ G and it is desired for each node to distinguish between its left and right G-neighbors.
Cite as
Yuval Gil and Merav Parter. New Distributed Interactive Proofs for Planarity: A Matter of Left and Right. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 34:1-34:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{gil_et_al:LIPIcs.DISC.2025.34,
author = {Gil, Yuval and Parter, Merav},
title = {{New Distributed Interactive Proofs for Planarity: A Matter of Left and Right}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {34:1--34:23},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.34},
URN = {urn:nbn:de:0030-drops-248515},
doi = {10.4230/LIPIcs.DISC.2025.34},
annote = {Keywords: Distributed interactive proofs, Planar graphs}
}
Document
PIPQ: Strict Insert-Optimized Concurrent Priority Queue
Abstract
This paper presents PIPQ, a strict and linearizable concurrent priority queue whose design differs from existing solutions in literature because it focuses on enabling parallelism of insert operations as opposed to accelerating delete-min operations, as traditionally done. In a nutshell, PIPQ’s structure includes two levels: the worker level and the leader level. The worker level provides per-thread data structures enabling fast and parallel insertions. The leader level contains the highest priority elements in the priority queue and can thus serve delete-min operations. Our evaluation, which includes an exploration of different data access patterns, operation mixes, runtime settings, and an integration into a graph-based application, shows that PIPQ outperforms competitors in a variety of cases, especially with insert-dominant workloads.
Cite as
Olivia Grimes, Ahmed Hassan, Panagiota Fatourou, and Roberto Palmieri. PIPQ: Strict Insert-Optimized Concurrent Priority Queue. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 35:1-35:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{grimes_et_al:LIPIcs.DISC.2025.35,
author = {Grimes, Olivia and Hassan, Ahmed and Fatourou, Panagiota and Palmieri, Roberto},
title = {{PIPQ: Strict Insert-Optimized Concurrent Priority Queue}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {35:1--35:23},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.35},
URN = {urn:nbn:de:0030-drops-248525},
doi = {10.4230/LIPIcs.DISC.2025.35},
annote = {Keywords: Priority Queue, Concurrent Data Structures, Synchronization}
}
Document
LMQ-Sketch: Lagom Multi-Query Sketch for High-Rate Online Analytics
Abstract
Data sketches balance resource efficiency with controllable approximations for extracting features in high-volume, high-rate data. Two important points of interest are highlighted separately in recent works; namely, to (1) answer multiple types of queries from a single data structure built in one pass over the data, and (2) perform both queries and updates concurrently. In this work, we now tackle the new challenges arising when combining these useful directions together.
We investigate the trade-offs around efficiency, consistency, and accuracy to be balanced and synthesize key ideas into LMQ-Sketch, a single, composite data sketch supporting concurrent updates and multiple queries (frequency point queries, frequency moments F₁, and F₂ as representative selection). Our method "Lagom" is a cornerstone of LMQ-Sketch for low-latency global querying (<100µs), combining freshness, timeliness, and accuracy with a low memory footprint and high throughput (>2B updates/s). We analyze and evaluate the accuracy of Lagom, which builds on a simple geometric argument and efficiently combines work distribution with synchronization for proper concurrency semantics - monotonicity of operations and intermediate value linearizability. Comparing with state-of-the-art methods, which, as mentioned, provide either mixed queries or concurrency separately, LMQ-Sketch shows highly competitive throughput, with additional accuracy guarantees and concurrency semantics, while also reducing the required memory budget by an order of magnitude. We expect the methodology to have broader impact on concurrent multi-query sketches.
Cite as
Martin Hilgendorf and Marina Papatriantafilou. LMQ-Sketch: Lagom Multi-Query Sketch for High-Rate Online Analytics. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 36:1-36:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{hilgendorf_et_al:LIPIcs.DISC.2025.36,
author = {Hilgendorf, Martin and Papatriantafilou, Marina},
title = {{LMQ-Sketch: Lagom Multi-Query Sketch for High-Rate Online Analytics}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {36:1--36:24},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.36},
URN = {urn:nbn:de:0030-drops-248535},
doi = {10.4230/LIPIcs.DISC.2025.36},
annote = {Keywords: Concurrent Data Structures, Data Sketches, IVL, Freshness, Synchronization}
}
Document
Towards Optimal Distributed Edge Coloring with Fewer Colors
Abstract
There is a huge difference in techniques and runtimes of distributed algorithms for problems that can be solved by a sequential greedy algorithm and those that cannot. A prime example of this contrast appears in the edge coloring problem: while (2Δ-1)-edge coloring - where Δ is the maximum degree - can be solved in 𝒪(log^{∗}(n)) rounds on constant-degree graphs, the seemingly minor reduction to (2Δ-2) colors leads to an Ω(log n) lower bound [Chang, He, Li, Pettie & Uitto, SODA'18]. Understanding this sharp divide between very local problems and inherently more global ones remains a central open question in distributed computing and it is a core focus of this paper.
As our main contribution we design a deterministic distributed 𝒪(log n)-round reduction from the (2Δ-2)-edge coloring problem to the much easier (2Δ-1)-edge coloring problem. This reduction is optimal, as the (2Δ-2)-edge coloring problem admits an Ω(log n) lower bound that even holds on the class of constant-degree graphs, whereas the 2Δ-1-edge coloring problem can be solved in 𝒪(log^{∗}n) rounds. By plugging in the (2Δ-1)-edge coloring algorithms from [Balliu, Brandt, Kuhn & Olivetti, PODC'22] running in 𝒪(log^{12}Δ + log^{∗} n) rounds, we obtain an optimal runtime of 𝒪(log n) rounds as long as Δ = 2^{𝒪(log^{1/12} n)}. Previously, such an optimal algorithm was only known for the class of constant-degree graphs [Brandt, Maus, Narayanan, Schager & Uitto, SODA'25]. Furthermore, on general graphs our reduction improves the runtime from 𝒪̃(log³ n) to 𝒪̃(log^{5/3} n).
In addition, we also obtain an optimal 𝒪(log log n)-round randomized reduction of (2Δ - 2)-edge coloring to (2Δ - 1)-edge coloring. This leads to a 𝒪̃(log^{5/3} log n)-round (2Δ-2)-edge coloring algorithm, which beats the (very recent) previous state-of-the-art taking 𝒪̃(log^{8/3}log n) rounds from [Bourreau, Brandt & Nolin, STOC'25].
Lastly, we obtain an 𝒪(log_Δ n)-round reduction from the (2Δ-1)-edge coloring, albeit to the somewhat harder maximal independent set (MIS) problem.
Cite as
Manuel Jakob, Yannic Maus, and Florian Schager. Towards Optimal Distributed Edge Coloring with Fewer Colors. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 37:1-37:26, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{jakob_et_al:LIPIcs.DISC.2025.37,
author = {Jakob, Manuel and Maus, Yannic and Schager, Florian},
title = {{Towards Optimal Distributed Edge Coloring with Fewer Colors}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {37:1--37:26},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.37},
URN = {urn:nbn:de:0030-drops-248547},
doi = {10.4230/LIPIcs.DISC.2025.37},
annote = {Keywords: distributed graph algorithms, edge coloring, LOCAL model}
}
Document
Compact Routing Schemes in Undirected and Directed Graphs
Abstract
In this paper, we study the problem of compact routing schemes in weighted undirected and directed graphs.
For weighted undirected graphs, more than a decade ago, Chechik [PODC'13] presented a ≈ 3.68k-stretch compact routing scheme that uses Õ(n^{1/k}log{D}) local storage, where D is the normalized diameter, for every k > 1. We present a ≈ 2.64k-stretch compact routing scheme that uses Õ(n^{1/k}) local storage on average in each vertex. This is the first compact routing scheme that uses total local storage of Õ(n^{1+1/k}) while achieving a c ⋅ k stretch, for a constant c < 3.
In real-world network protocols, messages are usually transmitted as part of a communication session between two parties. Therefore, more than two decades ago, Thorup and Zwick [SPAA'01] considered compact routing schemes that establish a communication session using a handshake. In their handshake-based compact routing scheme, the handshake is routed along a (4k-5)-stretch path, and the rest of the communication session is routed along an optimal (2k-1)-stretch path. It is straightforward to improve the (4k-5)-stretch of the handshake to ≈ 3.68k-stretch using the compact routing scheme of Chechik [PODC'13]. We improve the handshake stretch to the optimal (2k-1), by borrowing the concept of roundtrip routing from directed graphs to undirected graphs.
For weighted directed graphs, more than two decades ago, Roditty, Thorup, and Zwick [SODA'02 and TALG'08] presented a (4k+ε)-stretch compact roundtrip routing scheme that uses Õ(n^{1/k}) local storage for every k ≥ 3. For k = 3, this gives a (12+ε)-roundtrip stretch using Õ(n^{1/3}) local storage. We improve the stretch by developing a 7-roundtrip stretch routing scheme with Õ(n^{1/3}) local storage. In addition, we consider graphs with bounded hop diameter and present an optimal (2k-1)-roundtrip stretch routing scheme that uses Õ(D_{HOP}⋅ n^{1/k}), where D_{HOP} is the hop diameter of the graph.
Cite as
Avi Kadria and Liam Roditty. Compact Routing Schemes in Undirected and Directed Graphs. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 38:1-38:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{kadria_et_al:LIPIcs.DISC.2025.38,
author = {Kadria, Avi and Roditty, Liam},
title = {{Compact Routing Schemes in Undirected and Directed Graphs}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {38:1--38:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.38},
URN = {urn:nbn:de:0030-drops-248555},
doi = {10.4230/LIPIcs.DISC.2025.38},
annote = {Keywords: Routing schemes, Compact routing schemes, Distance oracles, Computer networks, Graph algorithms}
}
Document
TEE Is Not a Healer: Rollback-Resistant Reliable Storage
Abstract
Recent advances in secure hardware technologies, such as Intel SGX or ARM TrustZone, offer an opportunity to substantially reduce the costs of Byzantine fault-tolerance by placing the program code and state within a secure enclave known as a Trusted Execution Environment (TEE). However, the protection offered by a TEE only applies during program execution. Once power is switched off, the non-volatile portion of the program state becomes vulnerable to rollback attacks wherein it is undetectably reverted to an older version. In this paper we consider the problem of implementing reliable read/write registers out of failure-prone replicas subject to state rollbacks. To this end, we introduce a new unified model that captures multiple failure types that can affect a TEE-based system and establish tight bounds on the fault-tolerance of register constructions in this model. We consider both the static case, where failure thresholds hold throughout the entire execution, and the dynamic case, where any number of replicas can roll back, provided these failures do not occur too often. Our dynamic register emulation algorithm, TEE-Rex , provides the first correct implementation of a distributed state recovery procedure that requires neither durable storage nor specialized hardware, such as trusted monotonic counters.
Cite as
Sadegh Keshavarzi, Gregory Chockler, and Alexey Gotsman. TEE Is Not a Healer: Rollback-Resistant Reliable Storage. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 39:1-39:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{keshavarzi_et_al:LIPIcs.DISC.2025.39,
author = {Keshavarzi, Sadegh and Chockler, Gregory and Gotsman, Alexey},
title = {{TEE Is Not a Healer: Rollback-Resistant Reliable Storage}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {39:1--39:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.39},
URN = {urn:nbn:de:0030-drops-248560},
doi = {10.4230/LIPIcs.DISC.2025.39},
annote = {Keywords: Trusted execution environments, fault tolerance, crash recovery}
}
Document
On the Randomized Locality of Matching Problems in Regular Graphs
Abstract
The main goal in distributed symmetry-breaking is to understand the locality of problems: the radius of the neighborhood that a node must explore to determine its part of a global solution. In this work, we study the locality of matching problems in the family of regular graphs, which is one of the main benchmarks for establishing lower bounds on the locality of symmetry-breaking problems, as well as for obtaining classification results. Our main results are summarized as follows:
1) Approximate matching: We develop randomized algorithms to show that (1 + ε)-approximate matching in regular graphs is truly local, i.e., the locality depends only on ε and is independent of all other graph parameters. Furthermore, as long as the degree Δ is not very small (namely, as long as Δ ≥ poly(1/ε)), this dependence is only logarithmic in 1/ε. This stands in sharp contrast to maximal matching in regular graphs which requires some dependence on the number of nodes n or the degree Δ.
2) Maximal matching: Our techniques further allow us to establish a strong separation between the node-averaged complexity and worst-case complexity of maximal matching in regular graphs, by showing that the former is only O(1).
Central to our main technical contribution is a novel martingale-based analysis for the ≈ 40-year-old algorithm by Luby. In particular, our analysis shows that applying one round of Luby’s algorithm on the line graph of a Δ-regular graph results in an almost Δ/2-regular graph.
Cite as
Seri Khoury, Manish Purohit, Aaron Schild, and Joshua R. Wang. On the Randomized Locality of Matching Problems in Regular Graphs. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 40:1-40:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{khoury_et_al:LIPIcs.DISC.2025.40,
author = {Khoury, Seri and Purohit, Manish and Schild, Aaron and Wang, Joshua R.},
title = {{On the Randomized Locality of Matching Problems in Regular Graphs}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {40:1--40:20},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.40},
URN = {urn:nbn:de:0030-drops-248570},
doi = {10.4230/LIPIcs.DISC.2025.40},
annote = {Keywords: regular graphs, maximum matching, augmenting paths, distributed algorithms, Luby’s algorithm, martingales}
}
Document
Natural Calamities Demand More Rescuers: Exploring Connectivity Time Dynamic Graphs
Abstract
We study the exploration problem by mobile agents in Connectivity Time dynamic graphs. The Connectivity Time model was introduced by Michail et al. [JPDC 2014] and is arguably one of the weakest dynamic graph connectivity models. We prove that exploration is impossible in such graphs using ((n-1)(n-2))/2 mobile agents starting from an arbitrary initial configuration, even when agents have full knowledge of system parameters, global communication, full visibility, and infinite memory. We then present an exploration algorithm that uses ((n-1)(n-2))/2 + 1 agents equipped with global communication, 1-hop visibility and O(log n) memory.
Cite as
Ashish Saxena and Kaushik Mondal. Natural Calamities Demand More Rescuers: Exploring Connectivity Time Dynamic Graphs. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 41:1-41:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{saxena_et_al:LIPIcs.DISC.2025.41,
author = {Saxena, Ashish and Mondal, Kaushik},
title = {{Natural Calamities Demand More Rescuers: Exploring Connectivity Time Dynamic Graphs}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {41:1--41:23},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.41},
URN = {urn:nbn:de:0030-drops-248585},
doi = {10.4230/LIPIcs.DISC.2025.41},
annote = {Keywords: Mobile agents, Anonymous graphs, Exploration, Dynamic graphs, Deterministic algorithm}
}
Document
Kudzu: Fast and Simple High-Throughput BFT
Abstract
We present Kudzu, a high-throughput atomic broadcast protocol with an integrated fast path. Our contribution is based on the combination of two lines of work. Firstly, our protocol achieves finality in just two rounds of communication if all but p out of n = 3f + 2p + 1 participating replicas behave correctly, where f is the number of Byzantine faults that are tolerated. Due to the seamless integration of the fast path, even in the presence of more than p faults, our protocol maintains state-of-the-art characteristics. Secondly, our protocol utilizes the bandwidth of participating replicas in a balanced way, alleviating the bottleneck at the leader, and thus enabling high throughput. This is achieved by disseminating blocks using erasure codes. Despite combining a novel set of advantages, Kudzu is remarkably simple: intricacies such as "progress certificates", complex view changes, and speculative execution are avoided.
Cite as
Victor Shoup, Jakub Sliwinski, and Yann Vonlanthen. Kudzu: Fast and Simple High-Throughput BFT. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 42:1-42:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{shoup_et_al:LIPIcs.DISC.2025.42,
author = {Shoup, Victor and Sliwinski, Jakub and Vonlanthen, Yann},
title = {{Kudzu: Fast and Simple High-Throughput BFT}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {42:1--42:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.42},
URN = {urn:nbn:de:0030-drops-248597},
doi = {10.4230/LIPIcs.DISC.2025.42},
annote = {Keywords: Consensus, Blockchain, Byzantine Fault Tolerance, Fast Path, State Machine Replication}
}
Document
Weight Reduction in Distributed Protocols: New Algorithms and Analysis
Abstract
We study the problem of minimizing the total weight of (potentially many) participants of a distributed protocol, a necessary step when the original values are large but the scheme to be deployed scales poorly with the weights. We assume that α fraction of the original weights can be corrupted and we must output new weights with at most β adversarial fraction, for α < β. This problem can be viewed from the prism of electing a small committee that does the heavy work, a powerful tool for making distributed protocols scalable. We solve the variant that requires giving parties potentially multiple seats in the committee and counting each seat towards the cost of the solution. Moreover, we focus on the "deterministic" version of the problem where the computed committee must be secure for any subset of parties that can be corrupted by the adversary; such a committee can be smaller than a randomly sampled one in some cases and is useful when security against adaptive corruptions is desired but parties in the sub-protocol speak multiple times.
Presented are new algorithms for the problem as well as analysis of prior work. We give two variants of the algorithm Swiper (PODC 2024), one that significantly improves the running time without sacrificing the quality of the output and the other improving the output for a reasonable increase in the running time. We prove, however, that all known algorithms, including our two variants of Swiper, have worst case approximation ratio Ω(n). To counter that, we give the first polynomial time algorithm with approximation factor n / log² n and also the first sub-exponential time exact algorithm, practical for some real-world inputs. Of theoretical interest is another polytime algorithm that we present, based on linear programming, whose output is no worse than an optimal solution to the problem with slightly different parameters.
We implemented and tested previous and new algorithms, comparing them on the stake distributions of popular proof-of-stake blockchains, and found that our second variant of Swiper computes solutions extremely close to the optimal, confirmed by our exact algorithm.
Cite as
Anatoliy Zinovyev. Weight Reduction in Distributed Protocols: New Algorithms and Analysis. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 43:1-43:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{zinovyev:LIPIcs.DISC.2025.43,
author = {Zinovyev, Anatoliy},
title = {{Weight Reduction in Distributed Protocols: New Algorithms and Analysis}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {43:1--43:24},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.43},
URN = {urn:nbn:de:0030-drops-248600},
doi = {10.4230/LIPIcs.DISC.2025.43},
annote = {Keywords: Weight reduction, distributed protocols, weighted cryptography, threshold cryptography, consensus, committee selection, adaptive corruptions, approximation algorithms, linear programming, rounding}
}
Document
Brief Announcement
Brief Announcement: Incrementally Verifiable Distributed Computation
Abstract
Incrementally verifiable computation (IVC) is a cryptographic scheme that allows a prover to certify the correctness of a long or ongoing computation in an incremental manner, by repeatedly updating a proof certifying the computation so far. Updating the proof does not require access to the entire trace of the computation, which makes the IVC prover memory efficient.
In this work we construct incrementally verifiable distributed computation, which allows a distributed algorithm to efficiently certify its own execution using low memory and communication overhead. Our primary motivation is massively-parallel computation (MPC), where memory efficiency is make-or-break: the machines participating in an MPC algorithm usually cannot store the entire trace of their computation. Thus, certifying MPC algorithms essentially requires distributed IVC.
At the heart of this work is a new abstraction, updatable batch arguments for {NP} (UpBARGs), which we define and construct. Standard BARGs allow one to prove a batch of k {NP}-statements using a proof whose length barely grows with k; however, the statements and their witnesses must all be known in advance. In contrast, UpBARGs support adding statements and witnesses on the fly, making them a flexible tool for constructing IVC across different computational models. We use UpBARGs to construct IVC for streaming algorithms, for MPC algorithms, and for PRAM algorithms in the exclusive-read exclusive-write (EREW) model.
Cite as
Eden Aldema Tshuva and Rotem Oshman. Brief Announcement: Incrementally Verifiable Distributed Computation. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 44:1-44:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{aldematshuva_et_al:LIPIcs.DISC.2025.44,
author = {Aldema Tshuva, Eden and Oshman, Rotem},
title = {{Brief Announcement: Incrementally Verifiable Distributed Computation}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {44:1--44:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.44},
URN = {urn:nbn:de:0030-drops-248829},
doi = {10.4230/LIPIcs.DISC.2025.44},
annote = {Keywords: Incrementally verifiable computation, massively parallel computation, streaming, parallel RAM, batch arguments, SNARG}
}
Document
Brief Announcement
Brief Announcement: DAGs for the Masses
Abstract
A recent approach to building consensus protocols on top of Directed Acyclic Graphs (DAGs) shows much promise due to its simplicity and stable throughput. However, as each node in the DAG typically includes a linear number of references to the nodes in the previous round, prior DAG protocols only scale up to a certain point when the overhead of maintaining the graph becomes the bottleneck.
To enable large-scale deployments of DAG-based protocols, we propose a sparse DAG architecture, where each node includes only a constant number of references to random nodes in the previous round. We present a sparse version of Bullshark - one of the most prominent DAG-based consensus protocols - and demonstrate its improved scalability.
Remarkably, unlike other protocols that use random sampling to reduce communication complexity, we manage to avoid sacrificing resilience: the protocol can tolerate up to f < n/3 Byzantine faults (where n is the number of participants), same as its less scalable deterministic counterpart. The proposed "sparse" methodology can be applied to any protocol that maintains disseminated system updates and causal relations between them in a graph-like structure. Our simulations show that the considerable reduction of transmitted metadata in sparse DAGs results in more efficient network utilization and better scalability.
Cite as
Michael Anoprenko, Andrei Tonkikh, Alexander Spiegelman, and Petr Kuznetsov. Brief Announcement: DAGs for the Masses. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 45:1-45:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{anoprenko_et_al:LIPIcs.DISC.2025.45,
author = {Anoprenko, Michael and Tonkikh, Andrei and Spiegelman, Alexander and Kuznetsov, Petr},
title = {{Brief Announcement: DAGs for the Masses}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {45:1--45:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.45},
URN = {urn:nbn:de:0030-drops-248617},
doi = {10.4230/LIPIcs.DISC.2025.45},
annote = {Keywords: Consensus, Atomic Broadcast, Byzantine Fault Tolerance, DAGs, Scalability, Sampling}
}
Document
Brief Announcement
Brief Announcement: Communication Patterns for Optimal Resilience
Abstract
In response to the impossibility of solving the consensus problem in asynchronous systems subject to failures, various relaxations of the consensus problem have been proposed, including approximate agreement, crusader agreement, gather, and reliable broadcast. Some are interesting in their own right while others are useful building blocks for solving other problems. We focus on message-passing systems of n processes, up to f of which can experience malicious (Byzantine) failures. These problems all require that n > 3f and they frequently have fairly simple and efficient algorithms when n > 5f. Challenges arise when considering resilience between 3f+1 and 5f. For instance, nearly twenty years elapsed between the discovery of an approximate agreement algorithm for n > 5f [Danny Dolev et al., 1986] and one for n > 3f [Abraham et al., 2004]. A stumbling block could be too much focus on looking for algorithms in a certain natural and intuitive form, which we call canonical (asynchronous) rounds. In such an algorithm, each process repeatedly sends a message containing its entire state tagged with a round number, then waits to receive n-f messages with that same round number, does some local computation and proceeds to the next round number. The n > 5f approximate agreement algorithm is in canonical round form but the n > 3f one is not.
For algorithms in canonical round form, an obvious way of measuring time is the number of canonical rounds until the algorithm completes. However, this approach does not apply to other algorithms, such as those in which processes wait to receive a certain number of messages that have other properties besides simply having a certain round number. Attempts to rewrite these latter algorithms in canonical round form can result in drastically increased round complexity. This blow-up in the round complexity is inherent, as we show in this paper that for a wide set of problems, there is no algorithm in canonical round form that has a finite upper bound on the number of rounds if n ≤ 5f. In contrast, the standard way of measuring time results in constant time complexity.
We first show the impossibility of a bounded number of canonical rounds for a generic problem that captures the key properties needed in the proof. The result then follows immediately for, most notably, crusader agreement and flavors of approximate agreement. We then show via reductions that the same result holds for reliable broadcast and gather, since there are crusader agreement algorithms that use reliable broadcast and gather with no round overhead.
Cite as
Hagit Attiya, Itay Flam, and Jennifer L. Welch. Brief Announcement: Communication Patterns for Optimal Resilience. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 46:1-46:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{attiya_et_al:LIPIcs.DISC.2025.46,
author = {Attiya, Hagit and Flam, Itay and Welch, Jennifer L.},
title = {{Brief Announcement: Communication Patterns for Optimal Resilience}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {46:1--46:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.46},
URN = {urn:nbn:de:0030-drops-248620},
doi = {10.4230/LIPIcs.DISC.2025.46},
annote = {Keywords: canonical rounds, reliable broadcast, gather, crusader agreement, approximate agreement, time complexity}
}
Document
Brief Announcement
Brief Announcement: Highly Dynamic and Fully Distributed Data Structures
Abstract
We study robust and efficient distributed algorithms for building and maintaining distributed data structures in dynamic Peer-to-Peer (P2P) networks. P2P networks are characterized by a high level of dynamicity with abrupt heavy node churn (nodes that join and leave the network continuously over time). We present a novel algorithmic framework to build and maintain, with high probability, a skip list for poly(n) rounds despite a churn rate of 𝒪(n/log n), which is the number of nodes joining and/or leaving per round; n is the stable network size. We assume that the churn is controlled by an oblivious adversary that has complete knowledge and control of what nodes join and leave and at what time and has unlimited computational power, but is oblivious to the random choices made by the algorithm. Importantly, the maintenance overhead in any interval of time (measured in terms of the total number of messages exchanged and the number of edges formed/deleted) is (up to log factors) proportional to the churn rate. Furthermore, the algorithm is scalable in that the messages are small (i.e., at most polylog(n) bits) and every node sends and receives at most polylog(n) messages per round.
To the best of our knowledge, our work provides the first-known fully-distributed data structure and associated algorithms that provably work under highly dynamic settings (i.e., high churn rate that is near-linear in n). Furthermore, the nodes operate in a localized manner.
Our framework crucially relies on new distributed and parallel algorithms to merge two n-element skip lists and delete a large subset of items, both in 𝒪(log n) rounds with high probability. These procedures may be of independent interest due to their elegance and potential applicability in other contexts in distributed data structures.
Finally, we believe that our framework can be generalized to other distributed and dynamic data structures including graphs, potentially leading to stable distributed computation despite heavy churn.
Cite as
John Augustine, Antonio Cruciani, and Iqra Altaf Gillani. Brief Announcement: Highly Dynamic and Fully Distributed Data Structures. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 47:1-47:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{augustine_et_al:LIPIcs.DISC.2025.47,
author = {Augustine, John and Cruciani, Antonio and Gillani, Iqra Altaf},
title = {{Brief Announcement: Highly Dynamic and Fully Distributed Data Structures}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {47:1--47:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.47},
URN = {urn:nbn:de:0030-drops-248636},
doi = {10.4230/LIPIcs.DISC.2025.47},
annote = {Keywords: Peer-to-peer network, dynamic network, data structure, churn, distributed algorithm, randomized algorithm}
}
Document
Brief Announcement
Brief Announcement: 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 query complexity) while maximizing the resilience 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. To the best of our knowledge, this is the first work to address the Download problem in asynchronous communication networks.
Cite as
John Augustine, Soumyottam Chatterjee, Valerie King, Manish Kumar, Shachar Meir, and David Peleg. Brief Announcement: Distributed Download from an External Data Source in Asynchronous Faulty Settings. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 48:1-48:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{augustine_et_al:LIPIcs.DISC.2025.48,
author = {Augustine, John and Chatterjee, Soumyottam and King, Valerie and Kumar, Manish and Meir, Shachar and Peleg, David},
title = {{Brief Announcement: Distributed Download from an External Data Source in Asynchronous Faulty Settings}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {48:1--48:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.48},
URN = {urn:nbn:de:0030-drops-248646},
doi = {10.4230/LIPIcs.DISC.2025.48},
annote = {Keywords: Byzantine Fault Tolerance, Blockchain Oracle, Data Retrieval Model, Distributed Download}
}
Document
Brief Announcement
Brief Announcement: Synchronization in Anonymous Networks Under Arbitrary Dynamics
Abstract
We present the δ-Synchronizer, which works in non-synchronous dynamic networks under minimal assumptions. Our model allows for arbitrary topological changes without any guarantee of eventual global or partial stabilization and assumes that nodes are anonymous. This deterministic synchronizer is the first that enables nodes to simulate a dynamic network synchronous algorithm for executions in a semi-synchronous dynamic environment under a weakly-fair node activation scheduler, despite the absence of a global clock, node ids, persistent connectivity or any assumptions about the edge dynamics (in both the synchronous and semi-synchronous environments). We make the following contributions: (1) we extend the definition of synchronizers to networks with arbitrary edge dynamics; (2) we present the first synchronizer from the semi-synchronous to the synchronous model in such networks; and (3) we present non-trivial applications of the proposed synchronizer to existing algorithms. We assume an extension of the Pull communication model by adding a single 1-bit multi-writer atomic register at each edge-port of a node. We show that this extension is needed and that synchronization in our setting is not possible without it. The δ-Synchronizer operates with memory overhead at the nodes that is asymptotically logarithmic on the runtime of the underlying synchronous algorithm being simulated - in particular, it is logarithmic for polynomial-time synchronous algorithms.
Cite as
Rida Bazzi, Anya Chaturvedi, Andréa W. Richa, and Peter Vargas. Brief Announcement: Synchronization in Anonymous Networks Under Arbitrary Dynamics. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 49:1-49:8, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{bazzi_et_al:LIPIcs.DISC.2025.49,
author = {Bazzi, Rida and Chaturvedi, Anya and Richa, Andr\'{e}a W. and Vargas, Peter},
title = {{Brief Announcement: Synchronization in Anonymous Networks Under Arbitrary Dynamics}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {49:1--49:8},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.49},
URN = {urn:nbn:de:0030-drops-248652},
doi = {10.4230/LIPIcs.DISC.2025.49},
annote = {Keywords: Synchronization, Anonymous Dynamic Networks, Arbitrary Dynamics}
}
Document
Brief Announcement
Brief Announcement: Weaker Assumptions for Asymmetric Trust
Abstract
In protocols 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. As a result, existing solutions introduce stronger assumptions to circumvent this limitation. We show that some requirements used by state-of-the-art approaches 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 an asymmetric asynchronous unauthenticated reliable broadcast algorithm that significantly weakens the assumptions needed to solve the problem. Our techniques are general and can be readily adapted to other core problems in the asymmetric trust setting.
Cite as
Christian Cachin and Juan Villacis. Brief Announcement: Weaker Assumptions for Asymmetric Trust. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 50:1-50:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{cachin_et_al:LIPIcs.DISC.2025.50,
author = {Cachin, Christian and Villacis, Juan},
title = {{Brief Announcement: Weaker Assumptions for Asymmetric Trust}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {50:1--50:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.50},
URN = {urn:nbn:de:0030-drops-248667},
doi = {10.4230/LIPIcs.DISC.2025.50},
annote = {Keywords: Asymmetric Trust, Quorum Systems, Reliable Broadcast}
}
Document
Brief Announcement
Brief Announcement: Non-Uniform Content-Oblivious Leader Election on Oriented Asynchronous Rings
Abstract
In this paper, we study the leader election problem in oriented ring networks under content-oblivious asynchronous message-passing systems, where an adversary may arbitrarily corrupt message contents.
Frei et al. (DISC 2024) recently presented a uniform terminating leader election algorithm for oriented rings in this setting, with message complexity O(n ID_{max}) on a ring of size n, where ID_{max} is the largest identifier in the system.
In this paper, we investigate the message complexity of leader election in this model, showing that no uniform algorithm can solve the problem if each process is limited to sending a constant number of messages in one direction.
Interestingly, this limitation hinges on the uniformity assumption. In the non-uniform setting - where processes know an upper bound U ≥ n on the ring size - we present an algorithm with message complexity O(n U ID_{min}), in which each process sends O(U ID_{min}) messages clockwise and only three messages counter-clockwise. Here, ID_{min} is the smallest identifier in the system. This dependence on the identifiers compares favorably with the dependence on ID_{max} of Frei et al. (DISC 2024).
We also show a non-uniform algorithm where each process sends O(U logID_{min}) messages in one direction and O(logID_{min}) in the other. The factor log ID_{min} is optimal, matching the lower bound of Frei et al. (DISC 2024).
Finally, in the anonymous setting, we propose a randomized algorithm where each process sends only O(log² U) messages, with a success probability of 1 - U^{-c}.
Cite as
Jérémie Chalopin, Yi-Jun Chang, Lyuting Chen, Giuseppe A. Di Luna, and Haoran Zhou. Brief Announcement: Non-Uniform Content-Oblivious Leader Election on Oriented Asynchronous Rings. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 51:1-51:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{chalopin_et_al:LIPIcs.DISC.2025.51,
author = {Chalopin, J\'{e}r\'{e}mie and Chang, Yi-Jun and Chen, Lyuting and Di Luna, Giuseppe A. and Zhou, Haoran},
title = {{Brief Announcement: Non-Uniform Content-Oblivious Leader Election on Oriented Asynchronous Rings}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {51:1--51:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.51},
URN = {urn:nbn:de:0030-drops-248675},
doi = {10.4230/LIPIcs.DISC.2025.51},
annote = {Keywords: Content-Oblivious Networks, Leader Election, Oriented Rings, Asynchronous Systems}
}
Document
Brief Announcement
Brief Announcement: From Few to Many Faults: Adaptive Byzantine Agreement with Optimal Communication
Abstract
We study the problem of Strong Byzantine Agreement and establish tight upper and lower bounds on communication complexity, parameterized by the actual number of Byzantine faults. Specifically, for a system of n parties tolerating up to t Byzantine faults, out of which only f ≤ t are actually faulty, we obtain the following results:
In the partially synchronous setting, we present the first Byzantine Agreement protocol that achieves adaptive communication complexity of 𝒪(n + t ⋅ f) words, which is asymptotically optimal. Our protocol has an optimal resilience of t < n/3.
In the asynchronous setting, we prove a lower bound of Ω(n + t²) on the expected number of messages, and design an almost matching protocol with an optimal resilience that solves agreement with 𝒪((n + t²)⋅ log n) words. Our main technical contribution in the asynchronous setting is the utilization of a bipartite expander graph that allows for low-cost information dissemination.
Cite as
Andrei Constantinescu, Marc Dufay, Anton Paramonov, and Roger Wattenhofer. Brief Announcement: From Few to Many Faults: Adaptive Byzantine Agreement with Optimal Communication. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 52:1-52:8, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{constantinescu_et_al:LIPIcs.DISC.2025.52,
author = {Constantinescu, Andrei and Dufay, Marc and Paramonov, Anton and Wattenhofer, Roger},
title = {{Brief Announcement: From Few to Many Faults: Adaptive Byzantine Agreement with Optimal Communication}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {52:1--52:8},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.52},
URN = {urn:nbn:de:0030-drops-248680},
doi = {10.4230/LIPIcs.DISC.2025.52},
annote = {Keywords: Byzantine Agreement, Communication Complexity, Adaptive Communication Complexity, Resilience}
}
Document
Brief Announcement
Brief Announcement: Maintaining a Bounded Degree Expander in Dynamic Peer-To-Peer Networks
Abstract
We study the problem of maintaining robust and sparse overlay networks in fully distributed settings where nodes continuously join and leave the system. This scenario closely models real-world unstructured peer-to-peer networks, where maintaining a well-connected yet low-degree communication graph is crucial. We generalize a recent protocol by Becchetti et al. [SODA 2020] that relies on a simple randomized connection strategy to build an expander topology with high probability to a dynamic networks with churn setting. In this work, the network dynamism is governed by an oblivious adversary that controls which nodes join and leave the system in each round. The adversary has full knowledge of the system and unbounded computational power, but cannot see the random choices made by the protocol. Our analysis builds on the framework of Augustine et al. [FOCS 2015], and shows that our distributed algorithm maintains a constant-degree expander graph with high probability, despite a continuous adversarial churn with a rate of up to 𝒪(n/polylog(n)) per round, where n is the stable network size. The protocol and proof techniques are not new, but together they resolve a specific open problem raised in prior work. The result is a simple, fully distributed, and churn-resilient protocol with provable guarantees that align with observed empirical behavior.
Cite as
Antonio Cruciani. Brief Announcement: Maintaining a Bounded Degree Expander in Dynamic Peer-To-Peer Networks. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 53:1-53:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{cruciani:LIPIcs.DISC.2025.53,
author = {Cruciani, Antonio},
title = {{Brief Announcement: Maintaining a Bounded Degree Expander in Dynamic Peer-To-Peer Networks}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {53:1--53:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.53},
URN = {urn:nbn:de:0030-drops-248691},
doi = {10.4230/LIPIcs.DISC.2025.53},
annote = {Keywords: Peer-to-peer network, dynamic network, churn, distributed algorithm, randomized algorithm}
}
Document
Brief Announcement
Brief Announcement: Faster CONGEST Approximation Algorithms for Maximum Weighted Independent Set in Sparse Graphs
Abstract
The maximum independent set problem is a classic optimization problem in graph theory that has also been studied quite intensively in the distributed setting. Although the problem is hard to approximate within reasonable factors in general, there are good approximation algorithms known for several sparse graph families. In the present paper, we consider deterministic distributed CONGEST algorithms for the weighted version of the problem in trees and graphs of bounded arboricity (i.e., hereditary sparse graphs).
For trees, we prove that the task of deterministically computing a (1-ε)-approximate solution to the maximum weight independent set (MWIS) problem has a tight Θ(log^*(n) / ε) complexity. The lower bound already holds on unweighted oriented paths. On the upper bound side, we show that the bound can be achieved even in unrooted trees.
For graphs G = (V,E) of arboricity β > 1, we give two algorithms. If the sum of all node weights is w(V), we show that for any ε > 0, an independent set of weight at least (1-ε)⋅(w(V))/(4β) can be computed in O(log²(β/ε)/ε + log^* n) rounds. This result is obtained by a direct application of the local rounding framework of Faour, Ghaffari, Grunau, Kuhn, and Rozhoň [SODA ‘23]. We further show that for any ε > 0, an independent set of weight at least (1-ε)⋅(w(V))/(2β+1) can be computed in O(log³(β)⋅log(1/ε)/ε² ⋅log n) rounds. For ε = ω(1/√{β}), this significantly improves on a recent result of Gil [OPODIS ‘23], who showed that a 1/⌊(2+ε)β⌋-approximation to the MWIS problem can be computed in O(β/ε⋅log n) rounds. As an intermediate step to our result, we design an algorithm to compute an independent set of total weight at least (1-ε)⋅∑_{v ∈ V}(w(v))/(deg(v)+1) in time O(log³(Δ)⋅log(1/ε)/ε + log^* n), where Δ is the maximum degree of the graph.
Cite as
Salwa Faour and Fabian Kuhn. Brief Announcement: Faster CONGEST Approximation Algorithms for Maximum Weighted Independent Set in Sparse Graphs. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 54:1-54:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{faour_et_al:LIPIcs.DISC.2025.54,
author = {Faour, Salwa and Kuhn, Fabian},
title = {{Brief Announcement: Faster CONGEST Approximation Algorithms for Maximum Weighted Independent Set in Sparse Graphs}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {54:1--54:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.54},
URN = {urn:nbn:de:0030-drops-248704},
doi = {10.4230/LIPIcs.DISC.2025.54},
annote = {Keywords: CONGEST model, weighted independent set, approximation, trees, arboricity}
}
Document
Brief Announcement
Brief Announcement: Concurrent Double-Ended Priority Queues
Abstract
This work provides the first concurrent implementation of a double-ended priority queue (DEPQ). We describe a general way to add an ExtractMax operation to any concurrent priority queue that already supports Insert and ExtractMin.
Cite as
Panagiota Fatourou, Eric Ruppert, and Ioannis Xiradakis. Brief Announcement: Concurrent Double-Ended Priority Queues. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 55:1-55:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{fatourou_et_al:LIPIcs.DISC.2025.55,
author = {Fatourou, Panagiota and Ruppert, Eric and Xiradakis, Ioannis},
title = {{Brief Announcement: Concurrent Double-Ended Priority Queues}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {55:1--55:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.55},
URN = {urn:nbn:de:0030-drops-248719},
doi = {10.4230/LIPIcs.DISC.2025.55},
annote = {Keywords: shared-memory, data structure, double-ended, priority queue, priority deque, heap, skip list, combining}
}
Document
Brief Announcement
Brief Announcement: Universal Dancing by Luminous Robots Under Sequential Schedulers
Abstract
The Dancing problem requires a swarm of n autonomous mobile robots to form a sequence of patterns, aka perform a choreography. Existing work has proven that some crucial restrictions on choreographies and initial configurations (e.g., on repetitions of patterns, periodicity, symmetries, contractions/expansions) must hold so that the Dancing problem can be solved under certain robot models. Here, we prove that these necessary constraints can be dropped by considering the LUMI model (i.e., where robots are endowed with a light whose color can be chosen from a constant-size palette) under the quite unexplored sequential scheduler. We formalize the class of Universal Dancing problems which require a swarm of n robots starting from any initial configuration to perform a (periodic or finite) sequence of arbitrary patterns, only provided that each pattern consists of n vertices (including multiplicities). However, we prove that, to be solvable under LUMI, the length of the feasible choreographies is bounded by the compositions of n into the number of colors available to the robots. We provide an algorithm solving the Universal Dancing problem by exploiting the peculiar capability of sequential robots to implement a distributed counter mechanism. Even assuming non-rigid movements, our algorithm ensures spatial homogeneity of the performed choreography.
Cite as
Caterina Feletti, Paola Flocchini, Debasish Pattanayak, Giuseppe Prencipe, and Nicola Santoro. Brief Announcement: Universal Dancing by Luminous Robots Under Sequential Schedulers. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 56:1-56:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{feletti_et_al:LIPIcs.DISC.2025.56,
author = {Feletti, Caterina and Flocchini, Paola and Pattanayak, Debasish and Prencipe, Giuseppe and Santoro, Nicola},
title = {{Brief Announcement: Universal Dancing by Luminous Robots Under Sequential Schedulers}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {56:1--56:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.56},
URN = {urn:nbn:de:0030-drops-248724},
doi = {10.4230/LIPIcs.DISC.2025.56},
annote = {Keywords: Luminous Robots, Sequence of Patterns, Pattern Formation, Sequential Scheduler}
}
Document
Brief Announcement
Brief Announcement: The Virtue of Self-Consistency
Abstract
We show that self-consistency can be a crucial property for autonomous mobile robots.
Specifically, we consider the task of gathering three robots, placed adversarially in distinct locations in the Euclidean plane, in a single point. We assume the natural scheduler RoundRobin, which activates the robots in turns. An activated robot perceives all robot locations in an adversarially scaled, rotated, and mirrored Cartesian coordinate system with itself at the origin and then moves wherever it wants. We show that this task cannot be solved in the default robot model (without any consistency guarantees and no multiplicity detection) but becomes feasible if we assume self-consistency (i.e., no changes between the different activations of the same robot) of either the unit length (i.e., no scaling) or the compass (i.e., no rotating) by providing explicit algorithms.
Cite as
Fabian Frei and Koichi Wada. Brief Announcement: The Virtue of Self-Consistency. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 57:1-57:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{frei_et_al:LIPIcs.DISC.2025.57,
author = {Frei, Fabian and Wada, Koichi},
title = {{Brief Announcement: The Virtue of Self-Consistency}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {57:1--57:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.57},
URN = {urn:nbn:de:0030-drops-248737},
doi = {10.4230/LIPIcs.DISC.2025.57},
annote = {Keywords: Autonomous Mobile Robots, Distinct Gathering, Round Robin, Disorientation, Self-Consistency}
}
Document
Brief Announcement
Brief Announcement: 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. Brief Announcement: Optimal-Length Labeling Schemes for Fast Deterministic Communication in Radio Networks. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 58:1-58:8, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{ganczorz_et_al:LIPIcs.DISC.2025.58,
author = {Ganczorz, Adam and Jurdzinski, Tomasz and Pelc, Andrzej},
title = {{Brief Announcement: Optimal-Length Labeling Schemes for Fast Deterministic Communication in Radio Networks}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {58:1--58:8},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.58},
URN = {urn:nbn:de:0030-drops-248744},
doi = {10.4230/LIPIcs.DISC.2025.58},
annote = {Keywords: radio network, distributed algorithms, algorithms with advice, labeling scheme, broadcasting, gossiping}
}
Document
Brief Announcement
Brief Announcement: Carry the Tail in Consensus Protocols
Abstract
We present Carry-the-Tail, the first deterministic atomic broadcast protocol in partial synchrony that, after GST, simultaneously guarantees two desirable properties: (i) a constant fraction of commits are proposed by non-faulty leaders against tail-forking attacks, and (ii) optimal, worst-case quadratic communication under a cascade of faulty leaders. The solution also guarantees linear amortized communication, i.e., the steady-state is linear. Combining these two desirable properties was not simultaneously achieved previously: on one hand, prior atomic broadcast solutions achieve per-view linear word communication complexity. However, they face a significant degradation in throughput under tail-forking attack. On the other hand, existing solutions to tail-forking attacks require either quadratic communication steps or computationally-prohibitive SNARK generation.
The key technical contribution is Carry, a practical drop-in mechanism for streamlined protocols in the HotStuff family. Carry guarantees good performance against tail-forking and removes most leader-induced stalls, while retaining linear traffic and protocol simplicity. Carry-the-Tail implements the Carry mechanism on HotStuff-2.
Cite as
Suyash Gupta, Dakai Kang, Dahlia Malkhi, and Mohammad Sadoghi. Brief Announcement: Carry the Tail in Consensus Protocols. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 59:1-59:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{gupta_et_al:LIPIcs.DISC.2025.59,
author = {Gupta, Suyash and Kang, Dakai and Malkhi, Dahlia and Sadoghi, Mohammad},
title = {{Brief Announcement: Carry the Tail in Consensus Protocols}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {59:1--59:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.59},
URN = {urn:nbn:de:0030-drops-248759},
doi = {10.4230/LIPIcs.DISC.2025.59},
annote = {Keywords: Consensus, Blockchain, BFT}
}
Document
Brief Announcement
Brief Announcement: Distributed Sparsest Cut via Eigenvalue Estimation
Abstract
We give new, improved bounds for approximating the sparsest cut value or in other words the conductance ϕ of a graph in the CONGEST model. As our main result, we present an algorithm running in O(log² n/ϕ) rounds in which every vertex outputs a value ̃ ϕ satisfying ϕ ≤ ̃ ϕ ≤ √{2.01ϕ}. In most regimes, our algorithm improves significantly over the previously fastest algorithm for the problem [Chen, Meierhans, Probst Gutenberg, Saranurak; SODA 25]. Additionally, our result generalizes to k-way conductance.
We obtain these results, by approximating the eigenvalues of the normalized Laplacian matrix L: = I-Deg^{-1/2}ADeg^ {-1/2}, where, A is the adjacency matrix and Deg is the diagonal matrix with the weighted degrees on the diagonal. We show our algorithms are near-optimal by proving a lower bound for computing the smallest non-trivial eigenvalue of L, even in the stronger LOCAL model
The previous state of the art sparsest cut algorithm is in the technical realm of expander decompositions. Our algorithms, on the other hand, are relatively simple and easy to implement. At the core, they rely on the well-known power method, which comes down to repeatedly multiplying the Laplacian with a vector. This operation can be performed in a single round in the CONGEST model.
All our algorithms apply to weighted, undirected graphs. Our lower bounds apply even in unweighted graphs.
Cite as
Yannic Maus and Tijn de Vos. Brief Announcement: Distributed Sparsest Cut via Eigenvalue Estimation. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 60:1-60:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{maus_et_al:LIPIcs.DISC.2025.60,
author = {Maus, Yannic and de Vos, Tijn},
title = {{Brief Announcement: Distributed Sparsest Cut via Eigenvalue Estimation}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {60:1--60:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.60},
URN = {urn:nbn:de:0030-drops-248763},
doi = {10.4230/LIPIcs.DISC.2025.60},
annote = {Keywords: CONGEST, Sparsest Cut, Laplacian, Eigenvalues, Spectral Graph Theory}
}
Document
Brief Announcement
Brief Announcement: Asynchronous Approximate Agreement with Quadratic Communication
Abstract
We consider an asynchronous network of n message-sending parties, up to t of which are byzantine. We study approximate agreement, where the parties obtain approximately equal outputs in the convex hull of their inputs. In their seminal work, Abraham, Amit and Dolev [OPODIS '04] solve this problem in ℝ with the optimal resilience t < n/3 with a protocol where each party reliably broadcasts a value in every iteration. This takes Θ(n²) messages per reliable broadcast, or Θ(n³) messages per 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 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 recursively reduce the task to edge agreement in a subtree with a smaller centroid decomposition height. Then, we achieve edge agreement in the infinite path ℤ, again with the help of 2-graded consensus. Finally, we show that our edge agreement protocol enables ε-agreement in ℝ in 6log₂M/(ε) + 𝒪(log log M/(ε)) rounds with 𝒪(n² log M/(ε)) messages and 𝒪(n²log M/(ε)log log M/(ε)) bits of communication, where M is the maximum non-byzantine input magnitude.
Cite as
Mose Mizrahi Erbes and Roger Wattenhofer. Brief Announcement: Asynchronous Approximate Agreement with Quadratic Communication. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 61:1-61:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{mizrahierbes_et_al:LIPIcs.DISC.2025.61,
author = {Mizrahi Erbes, Mose and Wattenhofer, Roger},
title = {{Brief Announcement: Asynchronous Approximate Agreement with Quadratic Communication}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {61:1--61:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.61},
URN = {urn:nbn:de:0030-drops-248771},
doi = {10.4230/LIPIcs.DISC.2025.61},
annote = {Keywords: Approximate agreement, byzantine fault tolerance, communication complexity}
}
Document
Brief Announcement
Brief Announcement: Time, Fences and the Ordering of Events in TSO
Abstract
Total Store Order (TSO) is one of the most popular relaxed memory model in multiprocessor architectures, widely implemented, for example, in Intel’s x86 and x64 platforms. It delays write visibility via store buffers, thereby allowing a significant improvement in efficiency. This, however, complicates reasoning about correctness, as executions may violate sequential consistency. We present a semantic framework that provides effective tools that can pinpoint when such synchronization is necessary under TSO. We define a TSO-specific occurs-before relation, adapting Lamport’s happens-before to TSO, and prove that events at different sites can be temporally ordered only via an occurs-before chain. Analyzing how fences and RMWs create these chains lets us identify when they are unavoidable. We present in this BA how these results impact linearizable implementations of registers, capturing information flow and causality in TSO. The full version of this work provides details as well as results regarding the need for synchronization in linearizable implementations of additional objects.
Cite as
Raïssa Nataf and Yoram Moses. Brief Announcement: Time, Fences and the Ordering of Events in TSO. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 62:1-62:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{nataf_et_al:LIPIcs.DISC.2025.62,
author = {Nataf, Ra\"{i}ssa and Moses, Yoram},
title = {{Brief Announcement: Time, Fences and the Ordering of Events in TSO}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {62:1--62:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.62},
URN = {urn:nbn:de:0030-drops-248784},
doi = {10.4230/LIPIcs.DISC.2025.62},
annote = {Keywords: TSO, linearizability, happens before, fences, synchronization actions}
}
Document
Brief Announcement
Brief Announcement: Optimal Dispersion Under Asynchrony
Abstract
We study the dispersion problem in anonymous port-labeled graphs: k ≤ n mobile agents, each with a unique ID and initially located arbitrarily on the nodes of an n-node graph with maximum degree Δ, must autonomously relocate so that no node hosts more than one agent. Dispersion serves as a fundamental task in the distributed computing of mobile agents, and its complexity stems from key challenges in local coordination under anonymity and limited memory.
The goal is to minimize both the time to achieve dispersion and the memory required per agent. It is known that any algorithm requires Ω(k) time in the worst case, and Ω(log k) bits of memory per agent. A recent result [Kshemkalyani et al., 2025] gives an optimal O(k)-time algorithm in the synchronous setting and an O(k log k)-time algorithm in the asynchronous setting, both using O(log(k+Δ)) bits. We close the complexity gap in the asynchronous setting by presenting the first dispersion algorithm that runs in optimal O(k) time using O(log(k+Δ)) bits of memory per agent. Our solution relies on a novel technique for constructing a port-one tree in anonymous graphs, which may be of independent interest.
Cite as
Debasish Pattanayak, Ajay D. Kshemkalyani, Manish Kumar, Anisur Rahaman Molla, and Gokarna Sharma. Brief Announcement: Optimal Dispersion Under Asynchrony. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 63:1-63:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{pattanayak_et_al:LIPIcs.DISC.2025.63,
author = {Pattanayak, Debasish and Kshemkalyani, Ajay D. and Kumar, Manish and Molla, Anisur Rahaman and Sharma, Gokarna},
title = {{Brief Announcement: Optimal Dispersion Under Asynchrony}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {63:1--63:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.63},
URN = {urn:nbn:de:0030-drops-248795},
doi = {10.4230/LIPIcs.DISC.2025.63},
annote = {Keywords: Distributed algorithms, mobile agents, local communication, dispersion, asynchrony, port-one tree, time and memory complexity}
}
Document
Brief Announcement
Brief Announcement: Proximal Byzantine Agreement: Improved Accuracy for Fault-Tolerant Replicated Datastreams
Abstract
Approximate Byzantine Agreement (ABA) protocols enable nonfaulty replicas with different initial values to derive a values within a ε-neighborhood of each other, despite the presence of Byzantine behavior. While they give strong guarantees for this ε-agreement property, they tend to have weaker guarantees that the derived value is accurate with respect to some ground truth. Worse, they often have impractical requirements such as large replica sets proportional to data dimensionality, or a priori knowledge of the maximum distance between nonfaulty values.
In Stochastic Byzantine Agreement (SBA), the distribution of the nonfaulty values is the result of a stochastic process influenced by sensor measurement error or other sources of noise that affect system outputs. For these scenarios, we present Proximal Byzantine Agreement (PBA), a stochastic Byzantine agreement protocol which infers the most likely output of replicated computation based on the proposed values observed by each replica. Unlike ABA protocols, PBA prioritizes accuracy over agreement. PBA accuracy is relative to the variance of nonfaulty values, yielding comparatively more accurate results for noisy data, particularly when noise is asymmetric. Our evaluations demonstrate this accuracy scales with data dimensionality, outperforming or only mildly underperforming methods that require quorums with up to 10× more replicas and 4× to 124× more computation time per agreement decision, even at relatively low dimensions (d = 4 to d = 18).
Cite as
Roy Shadmon and Owen Arden. Brief Announcement: Proximal Byzantine Agreement: Improved Accuracy for Fault-Tolerant Replicated Datastreams. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 64:1-64:8, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{shadmon_et_al:LIPIcs.DISC.2025.64,
author = {Shadmon, Roy and Arden, Owen},
title = {{Brief Announcement: Proximal Byzantine Agreement: Improved Accuracy for Fault-Tolerant Replicated Datastreams}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {64:1--64:8},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.64},
URN = {urn:nbn:de:0030-drops-248808},
doi = {10.4230/LIPIcs.DISC.2025.64},
annote = {Keywords: Byzantine fault tolerance, distributed control systems, robust statistics}
}
Document
Brief Announcement
Brief Announcement: Congested Clique Counting for Local Gibbs Distributions
Abstract
There are well established reductions between combinatorial sampling and counting problems (Jerrum, Valiant, Vazirani TCS 1986). Building off of a very recent parallel algorithm utilizing this connection (Liu, Yin, Zhang arxiv 2024), we demonstrate the first approximate counting algorithm in the CongestedClique for a wide range of problems. Most interestingly, we present an algorithm for approximating the number of q-colorings of a graph within ε-multiplicative error, when q > αΔ for any constant α > 2, in Õ((n^{1/3})/ε²) rounds. More generally, we achieve a runtime of Õ((n^{1/3})/ε²) rounds for approximating the partition function of Gibbs distributions defined over graphs when simple locality and fast mixing conditions hold. Gibbs distributions are widely used in fields such as machine learning and statistical physics. We obtain our result by providing an algorithm to draw n random samples from a distributed Markov chain in parallel, using similar ideas to triangle counting (Dolev, Lenzen, Peled DISC 2012) and semiring matrix multiplication (Censor-Hillel, Kaski, Korhonen, Lenzen, Paz, Suomela PODC 2015). Aside from counting problems, this result may be interesting for other applications requiring a large number of samples.
Cite as
Joshua Z. Sobel. Brief Announcement: Congested Clique Counting for Local Gibbs Distributions. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 65:1-65:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{sobel:LIPIcs.DISC.2025.65,
author = {Sobel, Joshua Z.},
title = {{Brief Announcement: Congested Clique Counting for Local Gibbs Distributions}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {65:1--65:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.65},
URN = {urn:nbn:de:0030-drops-248811},
doi = {10.4230/LIPIcs.DISC.2025.65},
annote = {Keywords: Distributed Sampling, Approximate Counting, Markov Chains, Gibbs Distributions}
}
Document
Brief Announcement
Brief Announcement: Single-Round Broadcast: Impossibility, Feasibility, and More
Abstract
Broadcast is a fundamental primitive that plays an important role in secure Multi-Party Computation (MPC) area. In this work, we revisit the broadcast with selective abort (hereafter, short for broadcast) proposed by Goldwasser and Lindell (DISC 2002; JoC 2005) and study the round complexity of broadcast under different setup assumptions. Our findings are summarized as follows:
- We formally prove that 1-round broadcast is impossible under various widely-used setup assumptions (e.g., plain model, random oracle model, and common reference string model, etc.), even if we consider the static security and the stand-alone framework. More concretely, we formalize a notion called consistent oracle to capture these setups, and prove that our impossibility holds under the consistent oracle. Our impossibility holds in both honest majority setting and dishonest majority setting.
- We show that 1-round broadcast protocol is possible in the Universal Composition (UC) framework, by assuming stateful trusted hardwares. Our protocol can be proven secure against all-but-one adaptive and malicious corruptions. We bypass our impossibility result since our stateful trusted hardwares do not satisfy the definition of consistent oracle.
- We provide an application of 1-round broadcast: we construct the first 1-round multiple-verifier zero-knowledge (which is a special case of MPC) protocol, without assuming the broadcast hybrid world.
Cite as
Zhelei Zhou, Bingsheng Zhang, Hong-Sheng Zhou, and Kui Ren. Brief Announcement: Single-Round Broadcast: Impossibility, Feasibility, and More. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 66:1-66:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
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@InProceedings{zhou_et_al:LIPIcs.DISC.2025.66,
author = {Zhou, Zhelei and Zhang, Bingsheng and Zhou, Hong-Sheng and Ren, Kui},
title = {{Brief Announcement: Single-Round Broadcast: Impossibility, Feasibility, and More}},
booktitle = {39th International Symposium on Distributed Computing (DISC 2025)},
pages = {66:1--66:7},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-402-4},
ISSN = {1868-8969},
year = {2025},
volume = {356},
editor = {Kowalski, Dariusz R.},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.66},
URN = {urn:nbn:de:0030-drops-248838},
doi = {10.4230/LIPIcs.DISC.2025.66},
annote = {Keywords: Broadcast, Security with abort, Round optimality}
}