DROPS

Volume

OASIcs, Volume 97

3rd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2021)

Tokenomics 2021, November 18-19, 2021, New York University, USA (Virtual Conference)

Editors: Vincent Gramoli, Hanna Halaburda, and Rafael Pass

Volume

LIPIcs, Volume 217

25th International Conference on Principles of Distributed Systems (OPODIS 2021)

OPODIS 2021, December 13-15, 2021, Strasbourg, France

Editors: Quentin Bramas, Vincent Gramoli, and Alessia Milani

Volume

OASIcs, Volume 92

4th International Symposium on Foundations and Applications of Blockchain 2021 (FAB 2021)

FAB 2021, May 7, 2021, University of California, Davis, California, USA (Virtual Conference)

Editors: Vincent Gramoli and Mohammad Sadoghi

Document

DOI: 10.4230/LIPIcs.OPODIS.2025.21

Solving Tasks with Fewer Registers Than Processes

Authors: Eli Gafni, Giuliano Losa, Michel Raynal, and Gadi Taubenfeld

Published in: LIPIcs, Volume 361, 29th International Conference on Principles of Distributed Systems (OPODIS 2025)

Abstract

This paper studies distributed-computing tasks through the lens of space complexity in the read/write wait-free model, defined as the number of multi-reader-multi-writer atomic read/write registers needed to solve a task using a wait-free algorithm. Surprisingly, even though the read/write wait-free model is at the foundation of distributed computing, previous work on space complexity has focused on synchronization primitives stronger than read/write registers or on weaker progress conditions. The paper reveals that the read/write wait-free model offers a rich space-complexity landscape: (1) assuming non-anonymous processes, it shows that there is an infinite hierarchy of tasks of increasing space complexity; (2) it shows that space complexity separates anonymous from non-anonymous memory; (3) regardless of process or register anonymity, it exhibits a task of space complexity two, which is the minimal non-trivial space complexity; (4) finally, it shows that subcases of the adopt-commit task have different space complexity in non-anonymous memory under bounded wait-freedom.

Cite as

Eli Gafni, Giuliano Losa, Michel Raynal, and Gadi Taubenfeld. Solving Tasks with Fewer Registers Than Processes. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 21:1-21:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{gafni_et_al:LIPIcs.OPODIS.2025.21,
  author =	{Gafni, Eli and Losa, Giuliano and Raynal, Michel and Taubenfeld, Gadi},
  title =	{{Solving Tasks with Fewer Registers Than Processes}},
  booktitle =	{29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
  pages =	{21:1--21:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-409-3},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{361},
  editor =	{Arusoaie, Andrei and Onica, Emanuel and Spear, Michael and Tucci-Piergiovanni, Sara},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2025.21},
  URN =		{urn:nbn:de:0030-drops-251947},
  doi =		{10.4230/LIPIcs.OPODIS.2025.21},
  annote =	{Keywords: Asynchrony, Read/write registers, Wait-freedom, Tasks, Covering argument, Lower bound, Space complexity, Anonymous Processes, Anonymous Memory}
}

@InProceedings{gafni_et_al:LIPIcs.OPODIS.2025.21,
  author =	{Gafni, Eli and Losa, Giuliano and Raynal, Michel and Taubenfeld, Gadi},
  title =	{{Solving Tasks with Fewer Registers Than Processes}},
  booktitle =	{29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
  pages =	{21:1--21:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-409-3},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{361},
  editor =	{Arusoaie, Andrei and Onica, Emanuel and Spear, Michael and Tucci-Piergiovanni, Sara},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2025.21},
  URN =		{urn:nbn:de:0030-drops-251947},
  doi =		{10.4230/LIPIcs.OPODIS.2025.21},
  annote =	{Keywords: Asynchrony, Read/write registers, Wait-freedom, Tasks, Covering argument, Lower bound, Space complexity, Anonymous Processes, Anonymous Memory}
}

Document

DOI: 10.4230/LIPIcs.OPODIS.2025.33

Resolving Conflicts with Grace: Dynamically Concurrent Universality

Authors: Petr Kuznetsov and Nathan Josia Schrodt

Published in: LIPIcs, Volume 361, 29th International Conference on Principles of Distributed Systems (OPODIS 2025)

Abstract

Synchronization is the major obstacle to scalability in distributed computing. Concurrent operations on the shared data engage in synchronization when they encounter a conflict, i.e., their effects depend on the order in which they are applied. Ideally, one would like to detect conflicts in a dynamic manner, i.e., adjusting to the current system state. Indeed, it is very common that two concurrent operations conflict only in some rarely occurring states. In this paper, we define the notion of dynamic concurrency: an operation employs strong synchronization primitives only if it has to arbitrate with concurrent operations, given the current system state. We then present a dynamically concurrent universal construction.

Cite as

Petr Kuznetsov and Nathan Josia Schrodt. Resolving Conflicts with Grace: Dynamically Concurrent Universality. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 33:1-33:29, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{kuznetsov_et_al:LIPIcs.OPODIS.2025.33,
  author =	{Kuznetsov, Petr and Schrodt, Nathan Josia},
  title =	{{Resolving Conflicts with Grace: Dynamically Concurrent Universality}},
  booktitle =	{29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
  pages =	{33:1--33:29},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-409-3},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{361},
  editor =	{Arusoaie, Andrei and Onica, Emanuel and Spear, Michael and Tucci-Piergiovanni, Sara},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2025.33},
  URN =		{urn:nbn:de:0030-drops-252068},
  doi =		{10.4230/LIPIcs.OPODIS.2025.33},
  annote =	{Keywords: Universal Construction, Consensus, Dynamic Concurrency}
}

Document

DOI: 10.4230/LIPIcs.DISC.2025.2

On the Efficiency of Dynamic Transaction Scheduling in Blockchain Sharding

Authors: Ramesh Adhikari, Costas Busch, and Miroslav Popovic

Published in: LIPIcs, Volume 356, 39th International Symposium on Distributed Computing (DISC 2025)

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

Brief Announcement

DOI: 10.4230/LIPIcs.DISC.2025.59

Brief Announcement: Carry the Tail in Consensus Protocols

Authors: Suyash Gupta, Dakai Kang, Dahlia Malkhi, and Mohammad Sadoghi

Published in: LIPIcs, Volume 356, 39th International Symposium on Distributed Computing (DISC 2025)

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

DOI: 10.4230/LIPIcs.AFT.2025.18

From Permissioned to Proof-of-Stake Consensus

Authors: Jovan Komatovic, Andrew Lewis-Pye, Joachim Neu, Tim Roughgarden, and Ertem Nusret Tas

Published in: LIPIcs, Volume 354, 7th Conference on Advances in Financial Technologies (AFT 2025)

Abstract

This paper presents the first generic compiler that transforms any permissioned consensus protocol into a proof-of-stake permissionless consensus protocol. For each of the following properties, if the initial permissioned protocol satisfies that property in the partially synchronous setting, the consequent proof-of-stake protocol also satisfies that property in the partially synchronous and quasi-permissionless setting (with the same fault-tolerance): consistency; liveness; optimistic responsiveness; every composable log-specific property; and message complexity of a given order. Moreover, our transformation ensures that the output protocol satisfies accountability (identifying culprits in the event of a consistency violation), whether or not the original permissioned protocol satisfied it.

Cite as

Jovan Komatovic, Andrew Lewis-Pye, Joachim Neu, Tim Roughgarden, and Ertem Nusret Tas. From Permissioned to Proof-of-Stake Consensus. In 7th Conference on Advances in Financial Technologies (AFT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 354, pp. 18:1-18:26, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{komatovic_et_al:LIPIcs.AFT.2025.18,
  author =	{Komatovic, Jovan and Lewis-Pye, Andrew and Neu, Joachim and Roughgarden, Tim and Tas, Ertem Nusret},
  title =	{{From Permissioned to Proof-of-Stake Consensus}},
  booktitle =	{7th Conference on Advances in Financial Technologies (AFT 2025)},
  pages =	{18:1--18:26},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-400-0},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{354},
  editor =	{Avarikioti, Zeta and Christin, Nicolas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2025.18},
  URN =		{urn:nbn:de:0030-drops-247373},
  doi =		{10.4230/LIPIcs.AFT.2025.18},
  annote =	{Keywords: Permissioned Consensus, Proof-of-Stake, generic Compiler, Blockchain}
}

Document

DOI: 10.4230/LIPIcs.AFT.2025.13

Composable Byzantine Agreements with Reorder Attacks

Authors: Jing Chen, Jin Dong, Jichen Li, Xuanzhi Xia, and Wentao Zhou

Published in: LIPIcs, Volume 354, 7th Conference on Advances in Financial Technologies (AFT 2025)

Abstract

Byzantine agreement (BA) is a foundational building block in distributed systems that has been extensively studied for decades. With the growing demand for protocol composition in practice, the security analysis of BA protocols under multi-instance executions has attracted increasing attention. However, most existing adversary models focus solely on party corruption and neglect important threats posed by adversarial manipulations of communication channels in the network. Through channel attacks, messages can be reordered across multiple executions and lead to violations of the protocol’s security guarantees, without the participating parties being corrupted. In this work, we present the first adversary model that combines party corruption and channel attacks. Based on this model, we establish new security thresholds for Byzantine agreement under parallel and concurrent compositions, supported by complementary impossibility and possibility results that match each other to form a tight bound. For the impossibility result, we show that even authenticated Byzantine agreement protocols cannot be secure under parallel composition when n ≤ 3t or n ≤ 2c + 2t + 1, where t and c denote the number of corrupted parties and communication channels, respectively. For the possibility result, we prove the existence of secure protocols for unauthenticated Byzantine agreement under parallel and concurrent composition, when n > 3t and n > 2c+2t+1. More specifically, we provide a general black-box compiler that transforms any single-instance secure BA protocol into one that is secure under parallel executions, and we provide a non-black-box construction for concurrent compositions.

Cite as

Jing Chen, Jin Dong, Jichen Li, Xuanzhi Xia, and Wentao Zhou. Composable Byzantine Agreements with Reorder Attacks. In 7th Conference on Advances in Financial Technologies (AFT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 354, pp. 13:1-13:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{chen_et_al:LIPIcs.AFT.2025.13,
  author =	{Chen, Jing and Dong, Jin and Li, Jichen and Xia, Xuanzhi and Zhou, Wentao},
  title =	{{Composable Byzantine Agreements with Reorder Attacks}},
  booktitle =	{7th Conference on Advances in Financial Technologies (AFT 2025)},
  pages =	{13:1--13:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-400-0},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{354},
  editor =	{Avarikioti, Zeta and Christin, Nicolas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2025.13},
  URN =		{urn:nbn:de:0030-drops-247321},
  doi =		{10.4230/LIPIcs.AFT.2025.13},
  annote =	{Keywords: Byzantine agreement, protocol composition, channel reorder attack, security threshold}
}

Document

DOI: 10.4230/LIPIcs.AFT.2025.15

Beyond Optimal Fault-Tolerance

Authors: Andrew Lewis-Pye and Tim Roughgarden

Published in: LIPIcs, Volume 354, 7th Conference on Advances in Financial Technologies (AFT 2025)

Abstract

One of the most basic properties of a consensus protocol is its fault-tolerance - the maximum fraction of faulty participants that the protocol can tolerate without losing fundamental guarantees such as safety and liveness. Because of its importance, the optimal fault-tolerance achievable by any protocol has been characterized in a wide range of settings. For example, for state machine replication (SMR) protocols operating in the partially synchronous setting, it is possible to simultaneously guarantee consistency against α-bounded adversaries (i.e., adversaries that control less than an α fraction of the participants) and liveness against β-bounded adversaries if and only if α + 2β ≤ 1. This paper characterizes to what extent "better-than-optimal" fault-tolerance guarantees are possible for SMR protocols when the standard consistency requirement is relaxed to allow a bounded number r of consistency violations, each potentially leading to the rollback of recently finalized transactions. We prove that bounded rollback is impossible without additional timing assumptions and investigate protocols that tolerate and recover from consistency violations whenever message delays around the time of an attack are bounded by a parameter Δ^* (which may be arbitrarily larger than the parameter Δ that bounds post-GST message delays in the partially synchronous model). Here, a protocol’s fault-tolerance can be a non-constant function of r, and we prove, for each r, matching upper and lower bounds on the optimal "recoverable fault-tolerance" achievable by any SMR protocol. For example, for protocols that guarantee liveness against 1/3-bounded adversaries in the partially synchronous setting, a 5/9-bounded adversary can always cause one consistency violation but not two, and a 2/3-bounded adversary can always cause two consistency violations but not three. Our positive results are achieved through a generic "recovery procedure" that can be grafted on to any accountable SMR protocol and restores consistency following a violation while rolling back only transactions that were finalized in the previous 2Δ^* timesteps.

Cite as

Andrew Lewis-Pye and Tim Roughgarden. Beyond Optimal Fault-Tolerance. In 7th Conference on Advances in Financial Technologies (AFT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 354, pp. 15:1-15:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{lewispye_et_al:LIPIcs.AFT.2025.15,
  author =	{Lewis-Pye, Andrew and Roughgarden, Tim},
  title =	{{Beyond Optimal Fault-Tolerance}},
  booktitle =	{7th Conference on Advances in Financial Technologies (AFT 2025)},
  pages =	{15:1--15:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-400-0},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{354},
  editor =	{Avarikioti, Zeta and Christin, Nicolas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2025.15},
  URN =		{urn:nbn:de:0030-drops-247341},
  doi =		{10.4230/LIPIcs.AFT.2025.15},
  annote =	{Keywords: Distributed computing, consensus, recovery}
}

Document

DOI: 10.4230/LIPIcs.AFT.2025.17

Fully-Fluctuating Participation in Sleepy Consensus

Authors: Yuval Efron, Joachim Neu, and Toniann Pitassi

Published in: LIPIcs, Volume 354, 7th Conference on Advances in Financial Technologies (AFT 2025)

Abstract

Proof-of-work allows Bitcoin to boast security amidst arbitrary fluctuations in participation of miners throughout time, so long as, at any point in time, a majority of hash power is honest. In recent years, however, the pendulum has shifted in favor of proof-of-stake-based consensus protocols. There, the sleepy model is the most prominent model for handling fluctuating participation of nodes. However, to date, no protocol in the sleepy model rivals Bitcoin in its robustness to drastic fluctuations in participation levels, with state-of-the-art protocols making various restrictive assumptions. In this work, we present a new adversary model, called external adversary. Intuitively, in our model, corrupt nodes do not divulge information about their secret keys. In this model, we show that protocols in the sleepy model can meaningfully claim to remain secure against fully fluctuating participation, without compromising efficiency or corruption resilience. Our adversary model is quite natural, and arguably naturally captures the process via which malicious behavior arises in protocols, as opposed to traditional worst-case modeling. On top of which, the model is also theoretically appealing, circumventing a barrier established in a recent work of Malkhi, Momose, and Ren.

Cite as

Yuval Efron, Joachim Neu, and Toniann Pitassi. Fully-Fluctuating Participation in Sleepy Consensus. In 7th Conference on Advances in Financial Technologies (AFT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 354, pp. 17:1-17:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{efron_et_al:LIPIcs.AFT.2025.17,
  author =	{Efron, Yuval and Neu, Joachim and Pitassi, Toniann},
  title =	{{Fully-Fluctuating Participation in Sleepy Consensus}},
  booktitle =	{7th Conference on Advances in Financial Technologies (AFT 2025)},
  pages =	{17:1--17:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-400-0},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{354},
  editor =	{Avarikioti, Zeta and Christin, Nicolas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2025.17},
  URN =		{urn:nbn:de:0030-drops-247362},
  doi =		{10.4230/LIPIcs.AFT.2025.17},
  annote =	{Keywords: Sleepy Consensus, fully-fluctuating dynamic Participation}
}

Document

Track A: Algorithms, Complexity and Games

DOI: 10.4230/LIPIcs.ICALP.2025.35

Near-Optimal Directed Low-Diameter Decompositions

Authors: Karl Bringmann, Nick Fischer, Bernhard Haeupler, and Rustam Latypov

Published in: LIPIcs, Volume 334, 52nd International Colloquium on Automata, Languages, and Programming (ICALP 2025)

Abstract

Low Diameter Decompositions (LDDs) are invaluable tools in the design of combinatorial graph algorithms. While historically they have been applied mainly to undirected graphs, in the recent breakthrough for the negative-length Single Source Shortest Path problem, Bernstein, Nanongkai, and Wulff-Nilsen [FOCS '22] extended the use of LDDs to directed graphs for the first time. Specifically, their LDD deletes each edge with probability at most O(1/D ⋅ log²n), while ensuring that each strongly connected component in the remaining graph has a (weak) diameter of at most D. In this work, we make further advancements in the study of directed LDDs. We reveal a natural and intuitive (in hindsight) connection to Expander Decompositions, and leveraging this connection along with additional techniques, we establish the existence of an LDD with an edge-cutting probability of O(1/D ⋅ log n log log n). This improves the previous bound by nearly a logarithmic factor and closely approaches the lower bound of Ω(1/D ⋅ log n). With significantly more technical effort, we also develop two efficient algorithms for computing our LDDs: a deterministic algorithm that runs in time Õ(m poly(D)) and a randomized algorithm that runs in near-linear time Õ(m). We believe that our work provides a solid conceptual and technical foundation for future research relying on directed LDDs, which will undoubtedly follow soon.

Cite as

Karl Bringmann, Nick Fischer, Bernhard Haeupler, and Rustam Latypov. Near-Optimal Directed Low-Diameter Decompositions. In 52nd International Colloquium on Automata, Languages, and Programming (ICALP 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 334, pp. 35:1-35:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{bringmann_et_al:LIPIcs.ICALP.2025.35,
  author =	{Bringmann, Karl and Fischer, Nick and Haeupler, Bernhard and Latypov, Rustam},
  title =	{{Near-Optimal Directed Low-Diameter Decompositions}},
  booktitle =	{52nd International Colloquium on Automata, Languages, and Programming (ICALP 2025)},
  pages =	{35:1--35:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-372-0},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{334},
  editor =	{Censor-Hillel, Keren and Grandoni, Fabrizio and Ouaknine, Jo\"{e}l and Puppis, Gabriele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2025.35},
  URN =		{urn:nbn:de:0030-drops-234125},
  doi =		{10.4230/LIPIcs.ICALP.2025.35},
  annote =	{Keywords: Low Diameter Decompositions, Expander Decompositions, Directed Graphs}
}

Document

Tool Paper

DOI: 10.4230/OASIcs.FMBC.2025.13

A Benchmark Framework for Byzantine Fault Tolerance Testing Algorithms (Tool Paper)

Authors: João Miguel Louro Neto and Burcu Kulahcioglu Ozkan

Published in: OASIcs, Volume 129, 6th International Workshop on Formal Methods for Blockchains (FMBC 2025)

Abstract

Recent discoveries of vulnerabilities in the design and implementation of Byzantine fault-tolerant protocols underscore the need for testing and exploration techniques to ensure their correctness. While there has been some recent effort for automated test generation for BFT protocols, there is no benchmark framework available to systematically evaluate their performance. We present ByzzBench, a benchmark framework designed to evaluate the performance of testing algorithms in detecting Byzantine fault tolerance bugs. ByzzBench is designed for a standardized implementation of BFT protocols and their execution in a controlled testing environment. It controls the nondeterminism in the concurrency, network, and process faults in the protocol execution, enabling the functionality to enforce particular execution scenarios and thereby facilitating the implementation of testing algorithms for BFT protocols.

Cite as

João Miguel Louro Neto and Burcu Kulahcioglu Ozkan. A Benchmark Framework for Byzantine Fault Tolerance Testing Algorithms (Tool Paper). In 6th International Workshop on Formal Methods for Blockchains (FMBC 2025). Open Access Series in Informatics (OASIcs), Volume 129, pp. 13:1-13:11, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{louroneto_et_al:OASIcs.FMBC.2025.13,
  author =	{Louro Neto, Jo\~{a}o Miguel and Kulahcioglu Ozkan, Burcu},
  title =	{{A Benchmark Framework for Byzantine Fault Tolerance Testing Algorithms}},
  booktitle =	{6th International Workshop on Formal Methods for Blockchains (FMBC 2025)},
  pages =	{13:1--13:11},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-371-3},
  ISSN =	{2190-6807},
  year =	{2025},
  volume =	{129},
  editor =	{Marmsoler, Diego and Xu, Meng},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.FMBC.2025.13},
  URN =		{urn:nbn:de:0030-drops-230406},
  doi =		{10.4230/OASIcs.FMBC.2025.13},
  annote =	{Keywords: Byzantine Fault Tolerance, BFT Protocols, Automated Testing}
}

Document

DOI: 10.4230/LIPIcs.OPODIS.2024.32

Distributed Agreement in the Arrovian Framework

Authors: Kenan Wood, Hammurabi Mendes, and Jonad Pulaj

Published in: LIPIcs, Volume 324, 28th International Conference on Principles of Distributed Systems (OPODIS 2024)

Abstract

Preference aggregation is a fundamental problem in voting theory, in which public input rankings of a set of alternatives (called preferences) must be aggregated into a single preference that satisfies certain soundness properties. The celebrated Arrow Impossibility Theorem is equivalent to a distributed task in a synchronous fault-free system that satisfies properties such as respecting unanimous preferences, maintaining independence of irrelevant alternatives (IIA), and non-dictatorship, along with consensus since only one preference can be decided. In this work, we study a weaker distributed task in which crash faults are introduced, IIA is not required, and the consensus property is relaxed to either k-set agreement or ε-approximate agreement using any metric on the set of preferences. In particular, we prove several novel impossibility results for both of these tasks in both synchronous and asynchronous distributed systems. We additionally show that the impossibility for our ε-approximate agreement task using the Kendall tau or Spearman footrule metrics holds under extremely weak assumptions.

Cite as

Kenan Wood, Hammurabi Mendes, and Jonad Pulaj. Distributed Agreement in the Arrovian Framework. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 32:1-32:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{wood_et_al:LIPIcs.OPODIS.2024.32,
  author =	{Wood, Kenan and Mendes, Hammurabi and Pulaj, Jonad},
  title =	{{Distributed Agreement in the Arrovian Framework}},
  booktitle =	{28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
  pages =	{32:1--32:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-360-7},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{324},
  editor =	{Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.32},
  URN =		{urn:nbn:de:0030-drops-225686},
  doi =		{10.4230/LIPIcs.OPODIS.2024.32},
  annote =	{Keywords: Approximate Agreement, Set Agreement, Preference Aggregation, Voting Theory, Impossibility}
}

Document

DOI: 10.4230/LIPIcs.OPODIS.2024.35

Near-Optimal Resilient Labeling Schemes

Authors: Keren Censor-Hillel and Einav Huberman

Published in: LIPIcs, Volume 324, 28th International Conference on Principles of Distributed Systems (OPODIS 2024)

Abstract

Labeling schemes are a prevalent paradigm in various computing settings. In such schemes, an oracle is given an input graph and produces a label for each of its nodes, enabling the labels to be used for various tasks. Fundamental examples in distributed settings include distance labeling schemes, proof labeling schemes, advice schemes, and more. This paper addresses the question of what happens in a labeling scheme if some labels are erased, e.g., due to communication loss with the oracle or hardware errors. We adapt the notion of resilient proof-labeling schemes of Fischer, Oshman, Shamir [OPODIS 2021] and consider resiliency in general labeling schemes. A resilient labeling scheme consists of two parts - a transformation of any given labeling to a new one, executed by the oracle, and a distributed algorithm in which the nodes can restore their original labels given the new ones, despite some label erasures. Our contribution is a resilient labeling scheme that can handle F such erasures. Given a labeling of 𝓁 bits per node, it produces new labels with multiplicative and additive overheads of O(1) and O(log(F)), respectively. The running time of the distributed reconstruction algorithm is O(F+(𝓁⋅F)/log n) in the Congest model. This improves upon what can be deduced from the work of Bick, Kol, and Oshman [SODA 2022], for non-constant values of F. It is not hard to show that the running time of our distributed algorithm is optimal, making our construction near-optimal, up to the additive overhead in the label size.

Cite as

Keren Censor-Hillel and Einav Huberman. Near-Optimal Resilient Labeling Schemes. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 35:1-35:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{censorhillel_et_al:LIPIcs.OPODIS.2024.35,
  author =	{Censor-Hillel, Keren and Huberman, Einav},
  title =	{{Near-Optimal Resilient Labeling Schemes}},
  booktitle =	{28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
  pages =	{35:1--35:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-360-7},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{324},
  editor =	{Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.35},
  URN =		{urn:nbn:de:0030-drops-225713},
  doi =		{10.4230/LIPIcs.OPODIS.2024.35},
  annote =	{Keywords: Labeling schemes, Erasures}
}

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