20 Search Results for "Mostéfaoui, Achour"

Document
DOI: 10.4230/LIPIcs.OPODIS.2025.5
Tight Conditions for Binary-Output Tasks Under Crashes

Authors: Timothé Albouy, Antonio Fernández Anta, Chryssis Georgiou, Nicolas Nicolaou, and Junlang Wang

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

Abstract
This paper explores necessary and sufficient system conditions to solve distributed tasks with binary outputs (i.e., tasks with output values in {0,1}). We focus on the distinct output sets of values a task can produce (intentionally disregarding validity and value multiplicity), considering that some processes may output no value. In a distributed system with n processes, of which up to t ≤ n can crash, we provide a complete characterization of the tight conditions on n and t under which every class of tasks with binary outputs is solvable, for both synchronous and asynchronous systems. This output-set approach yields highly general results: it unifies multiple distributed computing problems, such as binary consensus and symmetry breaking, and it produces impossibility proofs that hold for stronger task formulations, including those that consider validity, account for value multiplicity, or move beyond binary outputs.
Cite as

Timothé Albouy, Antonio Fernández Anta, Chryssis Georgiou, Nicolas Nicolaou, and Junlang Wang. Tight Conditions for Binary-Output Tasks Under Crashes. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 5:1-5:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{albouy_et_al:LIPIcs.OPODIS.2025.5,
  author =	{Albouy, Timoth\'{e} and Fern\'{a}ndez Anta, Antonio and Georgiou, Chryssis and Nicolaou, Nicolas and Wang, Junlang},
  title =	{{Tight Conditions for Binary-Output Tasks Under Crashes}},
  booktitle =	{29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
  pages =	{5:1--5:24},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-409-3},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{361},
  editor =	{Arusoaie, Andrei and Onica, Emanuel and Spear, Michael and Tucci-Piergiovanni, Sara},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2025.5},
  URN =		{urn:nbn:de:0030-drops-251786},
  doi =		{10.4230/LIPIcs.OPODIS.2025.5},
  annote =	{Keywords: Distributed solvability, Asynchrony, Synchrony, Impossibility proofs, Binary-output tasks, Crash tolerance, Disagreement}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2025.9
Contention-Aware Cooperation

Authors: Timothé Albouy, Davide Frey, Mathieu Gestin, Michel Raynal, and François Taïani

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

Abstract
As shown by Reliable Broadcast and Consensus, cooperation among a set of independent computing entities (sequential processes) is crucial in fault-tolerant distributed computing. Considering n-process asynchronous message-passing systems where some processes may be Byzantine, this paper introduces a novel cooperation abstraction, Contention-Aware Cooperation (CAC). While Reliable Broadcast is a one-to-n cooperation abstraction and Consensus is an n-to-n cooperation abstraction, CAC is a d-to-n cooperation abstraction where d (1 ≤ d ≤ n) varies with each run and remains unknown to the processes. Correct processes accept the same set of 𝓁 pairs ⟨ v,i ⟩ (v is the value proposed by p_i) from the d proposer processes, where 1 ≤ 𝓁 ≤ d and (as d) 𝓁 remains unknown to the processes (except in specific cases). Those 𝓁 values are accepted one at a time, potentially in different orders at each process. In addition, CAC provides each process with an imperfect oracle that provides insights into the values that they may accept in the future. Interestingly, the CAC abstraction is particularly efficient in favorable circumstances, when the oracle becomes accurate, which processes can detect. To illustrate its practical utility, the paper details two applications leveraging CAC: a fast consensus implementation optimized for low contention (named Cascading Consensus), and a novel naming problem that can be solved under full asynchrony. All algorithms presented require signatures.
Cite as

Timothé Albouy, Davide Frey, Mathieu Gestin, Michel Raynal, and François Taïani. Contention-Aware Cooperation. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 9:1-9:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{albouy_et_al:LIPIcs.OPODIS.2025.9,
  author =	{Albouy, Timoth\'{e} and Frey, Davide and Gestin, Mathieu and Raynal, Michel and Ta\"{i}ani, Fran\c{c}ois},
  title =	{{Contention-Aware Cooperation}},
  booktitle =	{29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
  pages =	{9:1--9:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-409-3},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{361},
  editor =	{Arusoaie, Andrei and Onica, Emanuel and Spear, Michael and Tucci-Piergiovanni, Sara},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2025.9},
  URN =		{urn:nbn:de:0030-drops-251823},
  doi =		{10.4230/LIPIcs.OPODIS.2025.9},
  annote =	{Keywords: Agreement, Asynchronous message-passing system, Byzantine processes, Conflict detection, Consensus, Cooperation abstraction, Distributed computing, Fault tolerance, Optimistically terminating consensus, Short-naming}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2025.13
A General Input-Dependent Colorless Computability Theorem and Applications to Core-Dependent Adversaries

Authors: Yannis Coutouly and Emmanuel Godard

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

Abstract
Distributed computing tasks can be presented with a triple (ℐ,𝒪,Δ). The solvability of a colorless task on the Iterated Immediate Snapshot model (IIS) has been characterized by the Colorless Computability Theorem [Maurice Herlihy et al., 2013]. A recent paper [Yannis Coutouly and Emmanuel Godard, 2024] generalizes this theorem for any message adversaries ℳ ⊆ IIS by geometric methods. In 2001, Mostéfaoui, Rajsbaum, Raynal, and Roy [Achour Mostéfaoui et al., 2002] introduced condition-based adversaries. This setting considers a particular adversary that will be applied only to a subset of input configurations. In this setting, they studied the k-set agreement task with condition-based t-resilient adversaries and obtained a sufficient condition on the conditions that make k-Set Agreement solvable. In this paper we have three contributions: 1) We generalize the characterization of [Yannis Coutouly and Emmanuel Godard, 2024] to input-dependent adversaries, which means that the adversaries can change depending on the input configuration. 2) We show that core-resilient adversaries of IIS_n have the same computability power as the core-resilient adversaries of IIS_n where crashes only happen at the start. 3) Using the two previous contributions, we provide a necessary and sufficient characterization of the condition-based, core-dependent adversaries that can solve k-Set Agreement. We also distinguish four settings that may appear when presenting a distributed task as (ℐ,𝒪,Δ). Finally, in a later section, we present structural properties on the carrier map Δ. Such properties allow simpler proof, without changing the computability power of the task. Most of the proofs in this article leverage the topological framework used in distributed computing by using simple geometric constructions.
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Yannis Coutouly and Emmanuel Godard. A General Input-Dependent Colorless Computability Theorem and Applications to Core-Dependent Adversaries. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 13:1-13:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{coutouly_et_al:LIPIcs.OPODIS.2025.13,
  author =	{Coutouly, Yannis and Godard, Emmanuel},
  title =	{{A General Input-Dependent Colorless Computability Theorem and Applications to Core-Dependent Adversaries}},
  booktitle =	{29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
  pages =	{13:1--13:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-409-3},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{361},
  editor =	{Arusoaie, Andrei and Onica, Emanuel and Spear, Michael and Tucci-Piergiovanni, Sara},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2025.13},
  URN =		{urn:nbn:de:0030-drops-251862},
  doi =		{10.4230/LIPIcs.OPODIS.2025.13},
  annote =	{Keywords: colorless task, topological methods, geometric simplicial complex, k-set-agreement, t-resilient model, condition-based computability}
}
Document
DOI: 10.4230/LIPIcs.DISC.2025.1
ABEL: Perfect Asynchronous Byzantine Extension from List-Decoding

Authors: Ittai Abraham and Gilad Asharov

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

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.
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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
DOI: 10.4230/LIPIcs.DISC.2025.39
TEE Is Not a Healer: Rollback-Resistant Reliable Storage

Authors: Sadegh Keshavarzi, Gregory Chockler, and Alexey Gotsman

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

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
DOI: 10.4230/LIPIcs.DISC.2025.32
Coordination Through Stochastic Channels

Authors: Pierre Fraigniaud, Boaz Patt-Shamir, and Sergio Rajsbaum

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

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
DOI: 10.4230/LIPIcs.DISC.2025.28
Byzantine Consensus in the Random Asynchronous Model

Authors: George Danezis, Jovan Komatovic, Lefteris Kokoris-Kogias, Alberto Sonnino, and Igor Zablotchi

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

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
DOI: 10.4230/LIPIcs.DISC.2025.15
Asynchronous Latency and Fast Atomic Snapshot

Authors: João Paulo Bezerra, Luciano Freitas, Petr Kuznetsov, and Matthieu Rambaud

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

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
DOI: 10.4230/LIPIcs.DISC.2025.8
Auditable Shared Objects: From Registers to Synchronization Primitives

Authors: Hagit Attiya, Antonio Fernández Anta, Alessia Milani, Alexandre Rapetti, and Corentin Travers

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

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.
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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
DOI: 10.4230/LIPIcs.DISC.2025.42
Kudzu: Fast and Simple High-Throughput BFT

Authors: Victor Shoup, Jakub Sliwinski, and Yann Vonlanthen

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

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.
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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
DOI: 10.4230/LIPIcs.AFT.2025.12
How Much Public Randomness Do Modern Consensus Protocols Need?

Authors: Joseph Bonneau, Benedikt Bünz, Miranda Christ, and Yuval Efron

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

Abstract
Modern blockchain-based consensus protocols aim for efficiency (i.e., low communication and round complexity) while maintaining security against adaptive adversaries. These goals are usually achieved using a public randomness beacon to select roles for each participant. We examine to what extent this randomness is necessary. Specifically, we provide tight bounds on the amount of entropy a Byzantine Agreement protocol must consume from a beacon in order to enjoy efficiency and adaptive security. We first establish that no consensus protocol can simultaneously be efficient, be adaptively secure, and use O(log n) bits of beacon entropy. We then show this bound is tight and, in fact, a trilemma by presenting three consensus protocols that achieve any two of these three properties.
Cite as

Joseph Bonneau, Benedikt Bünz, Miranda Christ, and Yuval Efron. How Much Public Randomness Do Modern Consensus Protocols Need?. In 7th Conference on Advances in Financial Technologies (AFT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 354, pp. 12:1-12:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{bonneau_et_al:LIPIcs.AFT.2025.12,
  author =	{Bonneau, Joseph and B\"{u}nz, Benedikt and Christ, Miranda and Efron, Yuval},
  title =	{{How Much Public Randomness Do Modern Consensus Protocols Need?}},
  booktitle =	{7th Conference on Advances in Financial Technologies (AFT 2025)},
  pages =	{12:1--12:19},
  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.2025.12},
  URN =		{urn:nbn:de:0030-drops-247310},
  doi =		{10.4230/LIPIcs.AFT.2025.12},
  annote =	{Keywords: Consensus, Randomness Beacon}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2024.4
AMECOS: A Modular Event-Based Framework for Concurrent Object Specification

Authors: Timothé Albouy, Antonio Fernández Anta, Chryssis Georgiou, Mathieu Gestin, Nicolas Nicolaou, and Junlang Wang

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

Abstract
In this work, we introduce a modular framework for specifying distributed systems that we call AMECOS. Specifically, our framework departs from the traditional use of sequential specification, which presents limitations both on the specification expressiveness and implementation efficiency of inherently concurrent objects, as documented by Castañeda, Rajsbaum and Raynal in CACM 2023. Our framework focuses on the interactions between the various system components, specified as concurrent objects. Interactions are described with sequences of object events. This provides a modular way of specifying distributed systems and separates legality (object semantics) from other issues, such as consistency. We demonstrate the usability of our framework by (i) specifying various well-known concurrent objects, such as registers, shared memory, message-passing, reliable broadcast, and consensus, (ii) providing hierarchies of ordering semantics (namely, consistency hierarchy, memory hierarchy, and reliable broadcast hierarchy), and (iii) presenting a novel axiomatic proof of the impossibility of the well-known Consensus problem.
Cite as

Timothé Albouy, Antonio Fernández Anta, Chryssis Georgiou, Mathieu Gestin, Nicolas Nicolaou, and Junlang Wang. AMECOS: A Modular Event-Based Framework for Concurrent Object Specification. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 4:1-4:29, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{albouy_et_al:LIPIcs.OPODIS.2024.4,
  author =	{Albouy, Timoth\'{e} and Fern\'{a}ndez Anta, Antonio and Georgiou, Chryssis and Gestin, Mathieu and Nicolaou, Nicolas and Wang, Junlang},
  title =	{{AMECOS: A Modular Event-Based Framework for Concurrent Object Specification}},
  booktitle =	{28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
  pages =	{4:1--4:29},
  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.2024.4},
  URN =		{urn:nbn:de:0030-drops-225409},
  doi =		{10.4230/LIPIcs.OPODIS.2024.4},
  annote =	{Keywords: Concurrency, Object specification, Consistency conditions, Consensus impossibility}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2024.21
No Symmetric Broadcast Abstraction Characterizes k-Set-Agreement in Message-Passing Systems

Authors: Sylvain Gay, Achour Mostéfaoui, and Matthieu Perrin

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

Abstract
This paper explores the relationship between broadcast abstractions and the k-set agreement (k-SA) problem in crash-prone asynchronous distributed systems. It specifically investigates whether any broadcast abstraction is computationally equivalent to k-SA in message-passing systems. A key contribution of the paper is the delineation of the realm of "meaningful" broadcast abstractions, through the introduction of two new symmetry properties: compositionality and content-neutrality, inspired by the principle of network neutrality. Such preciseness in definition is essential for this paper’s scope, as our aim is not to characterize the computing power of a specific broadcast abstraction, but rather to explore the domain of broadcast abstractions as a whole, in search of a broadcast abstraction with certain characteristics. The paper’s main contribution is the proof that no broadcast abstraction, which is both content-neutral and compositional, is computationally equivalent to k-set agreement when 1 < k < n, in the crash-prone asynchronous message-passing model. To the best of our knowledge, this result represents the first instance of showing that a coordination problem cannot be expressed by an equivalent broadcast abstraction. It does not establish the absence of an implementation, but rather the absence of a specification that possesses certain properties.
Cite as

Sylvain Gay, Achour Mostéfaoui, and Matthieu Perrin. No Symmetric Broadcast Abstraction Characterizes k-Set-Agreement in Message-Passing Systems. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 21:1-21:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{gay_et_al:LIPIcs.OPODIS.2024.21,
  author =	{Gay, Sylvain and Most\'{e}faoui, Achour and Perrin, Matthieu},
  title =	{{No Symmetric Broadcast Abstraction Characterizes k-Set-Agreement in Message-Passing Systems}},
  booktitle =	{28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
  pages =	{21:1--21:20},
  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.2024.21},
  URN =		{urn:nbn:de:0030-drops-225573},
  doi =		{10.4230/LIPIcs.OPODIS.2024.21},
  annote =	{Keywords: Agreement problem, Asynchronous system, Broadcast abstraction, Communication abstraction, Compositionality, Message-passing system, Network neutrality, Process crash, k-Set agreement, Wait-free model, Total order broadcast}
}
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.2023.35
Atomic Register Abstractions for Byzantine-Prone Distributed Systems

Authors: Vincent Kowalski, Achour Mostéfaoui, and Matthieu Perrin

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

Abstract
The construction of the atomic register abstraction over crash-prone asynchronous message-passing systems has been extensively studied since the founding work of Attiya, Bar-Noy, and Dolev. It has been shown that t < n/2 (where t is the maximal number of processes that may be faulty) is a necessary and sufficient requirement to build an atomic register. However, little attention has been paid to systems where faulty processes may exhibit a Byzantine behavior. This paper studies three definitions of linearizable single-writer multi-reader registers encountered in the state of the art: Read/Write registers whose read perations return the last written value, Read/Write-Increment registers whose read perations return both the last written value and the number of previously written values, and Read/Append registers whose read perations return the sequence of all previously written values. More specifically, it compares their computing power and the necessary and sufficient conditions on the maximum ratio t/n which makes it possible to build reductions from one register to another. Namely, we prove that t < n/3 is necessary and sufficient to implement a Read/Write-Increment register from Read/Write registers whereas this bound is only t < n/2 for a reduction from a Read/Append register to Read/Write-Increment registers. Reduction algorithms meeting these bounds are also provided.
Cite as

Vincent Kowalski, Achour Mostéfaoui, and Matthieu Perrin. Atomic Register Abstractions for Byzantine-Prone Distributed Systems. In 27th International Conference on Principles of Distributed Systems (OPODIS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 286, pp. 35:1-35:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{kowalski_et_al:LIPIcs.OPODIS.2023.35,
  author =	{Kowalski, Vincent and Most\'{e}faoui, Achour and Perrin, Matthieu},
  title =	{{Atomic Register Abstractions for Byzantine-Prone Distributed Systems}},
  booktitle =	{27th International Conference on Principles of Distributed Systems (OPODIS 2023)},
  pages =	{35:1--35:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-308-9},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{286},
  editor =	{Bessani, Alysson and D\'{e}fago, Xavier and Nakamura, Junya and Wada, Koichi and Yamauchi, Yukiko},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2023.35},
  URN =		{urn:nbn:de:0030-drops-195257},
  doi =		{10.4230/LIPIcs.OPODIS.2023.35},
  annote =	{Keywords: Byzantine processes, Concurrent Object, Linearizability, Shared Register}
}
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