Search Results

Documents authored by Albouy, Timothé

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)

Copy BibTex To Clipboard

@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)

Copy BibTex To Clipboard

@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.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)

Copy BibTex To Clipboard

@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.2024.14
Near-Optimal Communication Byzantine Reliable Broadcast Under a Message Adversary

Authors: Timothé Albouy, Davide Frey, Ran Gelles, Carmit Hazay, Michel Raynal, Elad Michael Schiller, François Taïani, and Vassilis Zikas

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

Abstract
We address the problem of Reliable Broadcast in asynchronous message-passing systems with n nodes, of which up to t are malicious (faulty), in addition to a message adversary that can drop some of the messages sent by correct (non-faulty) nodes. We present a Message-Adversary-Tolerant Byzantine Reliable Broadcast (MBRB) algorithm that communicates O(|m|+nκ) bits per node, where |m| represents the length of the application message and κ = Ω(log n) is a security parameter. This communication complexity is optimal up to the parameter κ. This significantly improves upon the state-of-the-art MBRB solution (Albouy, Frey, Raynal, and Taïani, TCS 2023), which incurs communication of O(n|m|+n²κ) bits per node. Our solution sends at most 4n² messages overall, which is asymptotically optimal. Reduced communication is achieved by employing coding techniques that replace the need for all nodes to (re-)broadcast the entire application message m. Instead, nodes forward authenticated fragments of the encoding of m using an erasure-correcting code. Under the cryptographic assumptions of threshold signatures and vector commitments, and assuming n > 3t+2d, where the adversary drops at most d messages per broadcast, our algorithm allows at least 𝓁 = n - t - (1 + ε)d (for any arbitrarily low ε > 0) correct nodes to reconstruct m, despite missing fragments caused by the malicious nodes and the message adversary.
Cite as

Timothé Albouy, Davide Frey, Ran Gelles, Carmit Hazay, Michel Raynal, Elad Michael Schiller, François Taïani, and Vassilis Zikas. Near-Optimal Communication Byzantine Reliable Broadcast Under a Message Adversary. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 14:1-14:29, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

Copy BibTex To Clipboard

@InProceedings{albouy_et_al:LIPIcs.OPODIS.2024.14,
  author =	{Albouy, Timoth\'{e} and Frey, Davide and Gelles, Ran and Hazay, Carmit and Raynal, Michel and Schiller, Elad Michael and Ta\"{i}ani, Fran\c{c}ois and Zikas, Vassilis},
  title =	{{Near-Optimal Communication Byzantine Reliable Broadcast Under a Message Adversary}},
  booktitle =	{28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
  pages =	{14:1--14:29},
  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.2024.14},
  URN =		{urn:nbn:de:0030-drops-225503},
  doi =		{10.4230/LIPIcs.OPODIS.2024.14},
  annote =	{Keywords: Asynchronous message-passing, Byzantine fault-tolerance, Message adversary, Reliable broadcast, Erasure-correction codes, \{Threshold\} signatures, \{Vector commitments\}}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2024.41
Brief Announcement: Towards Optimal Communication Byzantine Reliable Broadcast Under a Message Adversary

Authors: Timothé Albouy, Davide Frey, Ran Gelles, Carmit Hazay, Michel Raynal, Elad Michael Schiller, François Taïani, and Vassilis Zikas

Published in: LIPIcs, Volume 319, 38th International Symposium on Distributed Computing (DISC 2024)

Abstract
We address the problem of Reliable Broadcast in asynchronous message-passing systems with n nodes, of which up to t are malicious (faulty), in addition to a message adversary that can drop some of the messages sent by correct (non-faulty) nodes. We present a Message-Adversary-Tolerant Byzantine Reliable Broadcast (MBRB) algorithm that communicates an almost optimal amount of O(|m|+n²κ) bits per node, where |m| represents the length of the application message and κ = Ω(log n) is a security parameter. This improves upon the state-of-the-art MBRB solution (Albouy, Frey, Raynal, and Taïani, TCS 2023), which incurs communication of O(n|m|+n²κ) bits per node. Our solution sends at most 4n² messages overall, which is asymptotically optimal. Reduced communication is achieved by employing coding techniques that replace the need for all nodes to (re-)broadcast the entire application message m. Instead, nodes forward authenticated fragments of the encoding of m using an erasure-correcting code. Under the cryptographic assumptions of PKI and collision-resistant hash, and assuming n > 3t+2d, where the adversary drops at most d messages per broadcast, our algorithm allows at least 𝓁 = n - t - (1 + ε)d (for any ε > 0) correct nodes to reconstruct m, despite missing fragments caused by the malicious nodes and the message adversary.
Cite as

Timothé Albouy, Davide Frey, Ran Gelles, Carmit Hazay, Michel Raynal, Elad Michael Schiller, François Taïani, and Vassilis Zikas. Brief Announcement: Towards Optimal Communication Byzantine Reliable Broadcast Under a Message Adversary. In 38th International Symposium on Distributed Computing (DISC 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 319, pp. 41:1-41:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

Copy BibTex To Clipboard

@InProceedings{albouy_et_al:LIPIcs.DISC.2024.41,
  author =	{Albouy, Timoth\'{e} and Frey, Davide and Gelles, Ran and Hazay, Carmit and Raynal, Michel and Schiller, Elad Michael and Ta\"{i}ani, Fran\c{c}ois and Zikas, Vassilis},
  title =	{{Brief Announcement: Towards Optimal Communication Byzantine Reliable Broadcast Under a Message Adversary}},
  booktitle =	{38th International Symposium on Distributed Computing (DISC 2024)},
  pages =	{41:1--41:7},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-352-2},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{319},
  editor =	{Alistarh, Dan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2024.41},
  URN =		{urn:nbn:de:0030-drops-212697},
  doi =		{10.4230/LIPIcs.DISC.2024.41},
  annote =	{Keywords: Asynchronous message-passing, Byzantine fault-tolerance, Message adversary, Reliable Broadcast}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2022.26
A Modular Approach to Construct Signature-Free BRB Algorithms Under a Message Adversary

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

Published in: LIPIcs, Volume 253, 26th International Conference on Principles of Distributed Systems (OPODIS 2022)

Abstract
This paper explores how reliable broadcast can be implemented without signatures when facing a dual adversary that can both corrupt processes and remove messages. More precisely, we consider an asynchronous n-process message-passing system in which up to t processes are Byzantine and where, at the network level, for each message broadcast by a correct process, an adversary can prevent up to d processes from receiving it (the integer d defines the power of the message adversary). So, unlike previous works, this work considers that not only can computing entities be faulty (Byzantine processes), but, in addition, that the network can also lose messages. To this end, the paper adopts a modular strategy and first introduces a new basic communication abstraction denoted k2𝓁-cast, which simplifies quorum engineering, and studies its properties in this new adversarial context. Then, the paper deconstructs existing signature-free Byzantine-tolerant asynchronous broadcast algorithms and, with the help of the k2𝓁-cast communication abstraction, reconstructs versions of them that tolerate both Byzantine processes and message adversaries. Interestingly, these reconstructed algorithms are also more efficient than the Byzantine-tolerant-only algorithms from which they originate.
Cite as

Timothé Albouy, Davide Frey, Michel Raynal, and François Taïani. A Modular Approach to Construct Signature-Free BRB Algorithms Under a Message Adversary. In 26th International Conference on Principles of Distributed Systems (OPODIS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 253, pp. 26:1-26:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

Copy BibTex To Clipboard

@InProceedings{albouy_et_al:LIPIcs.OPODIS.2022.26,
  author =	{Albouy, Timoth\'{e} and Frey, Davide and Raynal, Michel and Ta\"{i}ani, Fran\c{c}ois},
  title =	{{A Modular Approach to Construct Signature-Free BRB Algorithms Under a Message Adversary}},
  booktitle =	{26th International Conference on Principles of Distributed Systems (OPODIS 2022)},
  pages =	{26:1--26:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-265-5},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{253},
  editor =	{Hillel, Eshcar and Palmieri, Roberto and Rivi\`{e}re, Etienne},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2022.26},
  URN =		{urn:nbn:de:0030-drops-176464},
  doi =		{10.4230/LIPIcs.OPODIS.2022.26},
  annote =	{Keywords: Asynchronous system, Byzantine processes, Communication abstraction, Delivery predicate, Fault-Tolerance, Forwarding predicate, Message adversary, Message loss, Modularity, Quorum, Reliable broadcast, Signature-free algorithm, Two-phase commit}
}
Document
DOI: 10.4230/LIPIcs.DISC.2022.4
Good-Case Early-Stopping Latency of Synchronous Byzantine Reliable Broadcast: The Deterministic Case

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

Published in: LIPIcs, Volume 246, 36th International Symposium on Distributed Computing (DISC 2022)

Abstract
This paper considers the good-case latency of Byzantine Reliable Broadcast (BRB), i.e., the time taken by correct processes to deliver a message when the initial sender is correct, and an essential property for practical distributed systems. Although significant strides have been made in recent years on this question, progress has mainly focused on either asynchronous or randomized algorithms. By contrast, the good-case latency of deterministic synchronous BRB under a majority of Byzantine faults has been little studied. In particular, it was not known whether a good-case latency below the worst-case bound of t+1 rounds could be obtained under a Byzantine majority. In this work, we answer this open question positively and propose a deterministic synchronous Byzantine reliable broadcast that achieves a good-case latency of max(2,t+3-c) rounds, where t is the upper bound on the number of Byzantine processes, and c the number of effectively correct processes.
Cite as

Timothé Albouy, Davide Frey, Michel Raynal, and François Taïani. Good-Case Early-Stopping Latency of Synchronous Byzantine Reliable Broadcast: The Deterministic Case. In 36th International Symposium on Distributed Computing (DISC 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 246, pp. 4:1-4:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

Copy BibTex To Clipboard

@InProceedings{albouy_et_al:LIPIcs.DISC.2022.4,
  author =	{Albouy, Timoth\'{e} and Frey, Davide and Raynal, Michel and Ta\"{i}ani, Fran\c{c}ois},
  title =	{{Good-Case Early-Stopping Latency of Synchronous Byzantine Reliable Broadcast: The Deterministic Case}},
  booktitle =	{36th International Symposium on Distributed Computing (DISC 2022)},
  pages =	{4:1--4:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-255-6},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{246},
  editor =	{Scheideler, Christian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2022.4},
  URN =		{urn:nbn:de:0030-drops-171953},
  doi =		{10.4230/LIPIcs.DISC.2022.4},
  annote =	{Keywords: Reliable Broadcast, Byzantine Faults, Synchronous Systems, Good-case latency, Deterministic Algorithms}
}
Any Issues?
X

Feedback on the Current Page

CAPTCHA

Thanks for your feedback!

Feedback submitted to Dagstuhl Publishing

Could not send message

Please try again later or send an E-mail
© 2023-2026 Schloss Dagstuhl – LZI GmbH Schloss Dagstuhl – LZI GmbH About DROPS Imprint Privacy Contact