24 Search Results for "Bertrand, Nathalie"

Document
Invited Talk
DOI: 10.4230/LIPIcs.OPODIS.2023.1
From Consensus Research to Redbelly Network Pty Ltd (Invited Talk)

Authors: Vincent Gramoli

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

Abstract
Designing and implementing correctly a blockchain system requires collaborations across places and research fields. Redbelly, a company across Australia, India and USA, illustrates well this idea. It started in 2005 at OPODIS, where we published the Reconfigurable Distributed Storage to replace distributed participants offering a service without disrupting its availability. This line of work [V. Gramoli et al., 2021] was instrumental to reconfigure blockchains without introducing hard forks. The research on the consensus problem we initiated at IRISA [V. Gramoli, 2022] led to rethinking PBFT-like algorithms for the context of blockchain by getting rid of the leader that can act as the bottleneck of large networks [V. Gramoli and Q. Tang, 2023]. Our work on security led to disclosing vulnerabilities in Ethereum [Parinya Ekparinya et al., 2020] and then motivated us to formally verify blockchain consensus [Nathalie Bertrand et al., 2022]. Our work at the frontier of economics [Michael Spain et al., 2019] led us to prevent front-running attacks [Pouriya Zarbafian and Vincent Gramoli, 2023] and to incentivize rational players to behave [Alejandro Ranchal-Pedrosa and Vincent Gramoli, 2022]. Our system work at Cornell and then at EPFL was foundational in experimenting blockchains across the globe [Vincent Gramoli et al., 2023]. Although not anticipated at the time, this series of work progressively led the University of Sydney and CSIRO, and later Redbelly Network Pty Ltd, to design the Redbelly Blockchain [Tyler Crain et al., 2021; Deepal Tennakoon et al., 2023], the platform of choice for compliant asset tokenisation.
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Vincent Gramoli. From Consensus Research to Redbelly Network Pty Ltd (Invited Talk). In 27th International Conference on Principles of Distributed Systems (OPODIS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 286, pp. 1:1-1:2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{gramoli:LIPIcs.OPODIS.2023.1,
  author =	{Gramoli, Vincent},
  title =	{{From Consensus Research to Redbelly Network Pty Ltd}},
  booktitle =	{27th International Conference on Principles of Distributed Systems (OPODIS 2023)},
  pages =	{1:1--1:2},
  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.2023.1},
  URN =		{urn:nbn:de:0030-drops-194915},
  doi =		{10.4230/LIPIcs.OPODIS.2023.1},
  annote =	{Keywords: Innovations, Commercialisation}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2023.88
Checking Presence Reachability Properties on Parameterized Shared-Memory Systems

Authors: Nicolas Waldburger

Published in: LIPIcs, Volume 272, 48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023)

Abstract
We consider the verification of distributed systems composed of an arbitrary number of asynchronous processes. Processes are identical finite-state machines that communicate by reading from and writing to a shared memory. Beyond the standard model with finitely many registers, we tackle round-based shared-memory systems with fresh registers at each round. In the latter model, both the number of processes and the number of registers are unbounded, making verification particularly challenging. The properties studied are generic presence reachability objectives, which subsume classical questions such as safety or synchronization by expressing the presence or absence of processes in some states. In the more general round-based setting, we establish that the parameterized verification of presence reachability properties is PSPACE-complete. Moreover, for the roundless model with finitely many registers, we prove that the complexity drops down to NP-complete and we provide several natural restrictions that make the problem solvable in polynomial time.
Cite as

Nicolas Waldburger. Checking Presence Reachability Properties on Parameterized Shared-Memory Systems. In 48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 272, pp. 88:1-88:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{waldburger:LIPIcs.MFCS.2023.88,
  author =	{Waldburger, Nicolas},
  title =	{{Checking Presence Reachability Properties on Parameterized Shared-Memory Systems}},
  booktitle =	{48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023)},
  pages =	{88:1--88:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-292-1},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{272},
  editor =	{Leroux, J\'{e}r\^{o}me and Lombardy, Sylvain and Peleg, David},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2023.88},
  URN =		{urn:nbn:de:0030-drops-186225},
  doi =		{10.4230/LIPIcs.MFCS.2023.88},
  annote =	{Keywords: Verification, Parameterized models, Distributed algorithms}
}
Document
DOI: 10.4230/LIPIcs.FSTTCS.2022.32
Semilinear Representations for Series-Parallel Atomic Congestion Games

Authors: Nathalie Bertrand, Nicolas Markey, Suman Sadhukhan, and Ocan Sankur

Published in: LIPIcs, Volume 250, 42nd IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2022)

Abstract
We consider atomic congestion games on series-parallel networks, and study the structure of the sets of Nash equilibria and social local optima on a given network when the number of players varies. We establish that these sets are definable in Presburger arithmetic and that they admit semilinear representations whose all period vectors have a common direction. As an application, we prove that the prices of anarchy and stability converge to 1 as the number of players goes to infinity, and show how to exploit these semilinear representations to compute these ratios precisely for a given network and number of players.
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Nathalie Bertrand, Nicolas Markey, Suman Sadhukhan, and Ocan Sankur. Semilinear Representations for Series-Parallel Atomic Congestion Games. In 42nd IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 250, pp. 32:1-32:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{bertrand_et_al:LIPIcs.FSTTCS.2022.32,
  author =	{Bertrand, Nathalie and Markey, Nicolas and Sadhukhan, Suman and Sankur, Ocan},
  title =	{{Semilinear Representations for Series-Parallel Atomic Congestion Games}},
  booktitle =	{42nd IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2022)},
  pages =	{32:1--32:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-261-7},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{250},
  editor =	{Dawar, Anuj and Guruswami, Venkatesan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2022.32},
  URN =		{urn:nbn:de:0030-drops-174243},
  doi =		{10.4230/LIPIcs.FSTTCS.2022.32},
  annote =	{Keywords: congestion games, Nash equilibria, Presburger arithmetic, semilinear sets, price of anarchy}
}
Document
DOI: 10.4230/LIPIcs.DISC.2022.10
Holistic Verification of Blockchain Consensus

Authors: Nathalie Bertrand, Vincent Gramoli, Igor Konnov, Marijana Lazić, Pierre Tholoniat, and Josef Widder

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

Abstract
Blockchain has recently attracted the attention of the industry due, in part, to its ability to automate asset transfers. It requires distributed participants to reach a consensus on a block despite the presence of malicious (a.k.a. Byzantine) participants. Malicious participants exploit regularly weaknesses of these blockchain consensus algorithms, with sometimes devastating consequences. In fact, these weaknesses are quite common and are well illustrated by the flaws in various blockchain consensus algorithms [Pierre Tholoniat and Vincent Gramoli, 2019]. Paradoxically, until now, no blockchain consensus has been holistically verified. In this paper, we remedy this paradox by model checking for the first time a blockchain consensus used in industry. We propose a holistic approach to verify the consensus algorithm of the Red Belly Blockchain [Tyler Crain et al., 2021], for any number n of processes and any number f < n/3 of Byzantine processes. We decompose directly the algorithm pseudocode in two parts - an inner broadcast algorithm and an outer decision algorithm - each modelled as a threshold automaton [Igor Konnov et al., 2017], and we formalize their expected properties in linear-time temporal logic. We then automatically check the inner broadcasting algorithm, under a carefully identified fairness assumption. For the verification of the outer algorithm, we simplify the model of the inner algorithm by relying on its proven properties. Doing so, we formally verify, for any parameter, not only the safety properties of the Red Belly Blockchain consensus but also its liveness in less than 70 seconds.
Cite as

Nathalie Bertrand, Vincent Gramoli, Igor Konnov, Marijana Lazić, Pierre Tholoniat, and Josef Widder. Holistic Verification of Blockchain Consensus. In 36th International Symposium on Distributed Computing (DISC 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 246, pp. 10:1-10:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{bertrand_et_al:LIPIcs.DISC.2022.10,
  author =	{Bertrand, Nathalie and Gramoli, Vincent and Konnov, Igor and Lazi\'{c}, Marijana and Tholoniat, Pierre and Widder, Josef},
  title =	{{Holistic Verification of Blockchain Consensus}},
  booktitle =	{36th International Symposium on Distributed Computing (DISC 2022)},
  pages =	{10:1--10:24},
  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.2022.10},
  URN =		{urn:nbn:de:0030-drops-172019},
  doi =		{10.4230/LIPIcs.DISC.2022.10},
  annote =	{Keywords: Model checking, automata, logic, byzantine failure}
}
Document
Track B: Automata, Logic, Semantics, and Theory of Programming
DOI: 10.4230/LIPIcs.ICALP.2022.113
Parameterized Safety Verification of Round-Based Shared-Memory Systems

Authors: Nathalie Bertrand, Nicolas Markey, Ocan Sankur, and Nicolas Waldburger

Published in: LIPIcs, Volume 229, 49th International Colloquium on Automata, Languages, and Programming (ICALP 2022)

Abstract
We consider the parameterized verification problem for distributed algorithms where the goal is to develop techniques to prove the correctness of a given algorithm regardless of the number of participating processes. Motivated by an asynchronous binary consensus algorithm [James Aspnes, 2002], we consider round-based distributed algorithms communicating with shared memory. A particular challenge in these systems is that 1) the number of processes is unbounded, and, more importantly, 2) there is a fresh set of registers at each round. A verification algorithm thus needs to manage both sources of infinity. In this setting, we prove that the safety verification problem, which consists in deciding whether all possible executions avoid a given error state, is PSPACE-complete. For negative instances of the safety verification problem, we also provide exponential lower and upper bounds on the minimal number of processes needed for an error execution and on the minimal round on which the error state can be covered.
Cite as

Nathalie Bertrand, Nicolas Markey, Ocan Sankur, and Nicolas Waldburger. Parameterized Safety Verification of Round-Based Shared-Memory Systems. In 49th International Colloquium on Automata, Languages, and Programming (ICALP 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 229, pp. 113:1-113:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{bertrand_et_al:LIPIcs.ICALP.2022.113,
  author =	{Bertrand, Nathalie and Markey, Nicolas and Sankur, Ocan and Waldburger, Nicolas},
  title =	{{Parameterized Safety Verification of Round-Based Shared-Memory Systems}},
  booktitle =	{49th International Colloquium on Automata, Languages, and Programming (ICALP 2022)},
  pages =	{113:1--113:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-235-8},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{229},
  editor =	{Boja\'{n}czyk, Miko{\l}aj and Merelli, Emanuela and Woodruff, David P.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2022.113},
  URN =		{urn:nbn:de:0030-drops-164541},
  doi =		{10.4230/LIPIcs.ICALP.2022.113},
  annote =	{Keywords: Verification, Parameterized models, Distributed algorithms}
}
Document
Invited Talk
DOI: 10.4230/LIPIcs.OPODIS.2021.1
Distributed Algorithms: A Challenging Playground for Model Checking (Invited Talk)

Authors: Nathalie Bertrand

Published in: LIPIcs, Volume 217, 25th International Conference on Principles of Distributed Systems (OPODIS 2021)

Abstract
Distributed computing is increasingly spreading, in advanced technological applications as well as in our daily life. Failures in distributed algorithms can have important human and financial consequences, so that is is crucial to develop rigorous techniques to verify their correctness. Model checking is a model-based approach to formal verification, dating back the 80’s. It has been successfully applied first to hardware, and later to software verification. Distributed computing raises new challenges for the model checking community, and calls for the development of new verification techniques and tools. In particular, the parameterized verification paradigm is nowadays blooming to help proving automatically the correctness of distributed algorithms. In this invited talk, we present recent parameterized verification developments to automatically prove properties of some classical distributed algorithms.
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Nathalie Bertrand. Distributed Algorithms: A Challenging Playground for Model Checking (Invited Talk). In 25th International Conference on Principles of Distributed Systems (OPODIS 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 217, p. 1:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{bertrand:LIPIcs.OPODIS.2021.1,
  author =	{Bertrand, Nathalie},
  title =	{{Distributed Algorithms: A Challenging Playground for Model Checking}},
  booktitle =	{25th International Conference on Principles of Distributed Systems (OPODIS 2021)},
  pages =	{1:1--1:1},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-219-8},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{217},
  editor =	{Bramas, Quentin and Gramoli, Vincent and Milani, Alessia},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2021.1},
  URN =		{urn:nbn:de:0030-drops-157767},
  doi =		{10.4230/LIPIcs.OPODIS.2021.1},
  annote =	{Keywords: Verification, Distributed algorithms}
}
Document
Invited Paper
DOI: 10.4230/LIPIcs.CONCUR.2021.1
CONCUR Test-Of-Time Award 2021 (Invited Paper)

Authors: Nathalie Bertrand, Luca de Alfaro, Rob van Glabbeek, Catuscia Palamidessi, and Nobuko Yoshida

Published in: LIPIcs, Volume 203, 32nd International Conference on Concurrency Theory (CONCUR 2021)

Abstract
This short article announces the recipients of the CONCUR Test-of-Time Award 2021.
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Nathalie Bertrand, Luca de Alfaro, Rob van Glabbeek, Catuscia Palamidessi, and Nobuko Yoshida. CONCUR Test-Of-Time Award 2021 (Invited Paper). In 32nd International Conference on Concurrency Theory (CONCUR 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 203, pp. 1:1-1:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{bertrand_et_al:LIPIcs.CONCUR.2021.1,
  author =	{Bertrand, Nathalie and de Alfaro, Luca and van Glabbeek, Rob and Palamidessi, Catuscia and Yoshida, Nobuko},
  title =	{{CONCUR Test-Of-Time Award 2021}},
  booktitle =	{32nd International Conference on Concurrency Theory (CONCUR 2021)},
  pages =	{1:1--1:3},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-203-7},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{203},
  editor =	{Haddad, Serge and Varacca, Daniele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2021.1},
  URN =		{urn:nbn:de:0030-drops-143786},
  doi =		{10.4230/LIPIcs.CONCUR.2021.1},
  annote =	{Keywords: Concurrency, CONCUR Test-of-Time Award}
}
Document
DOI: 10.4230/LIPIcs.CONCUR.2021.7
Quantified Linear Temporal Logic over Probabilistic Systems with an Application to Vacuity Checking

Authors: Jakob Piribauer, Christel Baier, Nathalie Bertrand, and Ocan Sankur

Published in: LIPIcs, Volume 203, 32nd International Conference on Concurrency Theory (CONCUR 2021)

Abstract
Quantified linear temporal logic (QLTL) is an ω-regular extension of LTL allowing quantification over propositional variables. We study the model checking problem of QLTL-formulas over Markov chains and Markov decision processes (MDPs) with respect to the number of quantifier alternations of formulas in prenex normal form. For formulas with k{-}1 quantifier alternations, we prove that all qualitative and quantitative model checking problems are k-EXPSPACE-complete over Markov chains and k{+}1-EXPTIME-complete over MDPs. As an application of these results, we generalize vacuity checking for LTL specifications from the non-probabilistic to the probabilistic setting. We show how to check whether an LTL-formula is affected by a subformula, and also study inherent vacuity for probabilistic systems.
Cite as

Jakob Piribauer, Christel Baier, Nathalie Bertrand, and Ocan Sankur. Quantified Linear Temporal Logic over Probabilistic Systems with an Application to Vacuity Checking. In 32nd International Conference on Concurrency Theory (CONCUR 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 203, pp. 7:1-7:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{piribauer_et_al:LIPIcs.CONCUR.2021.7,
  author =	{Piribauer, Jakob and Baier, Christel and Bertrand, Nathalie and Sankur, Ocan},
  title =	{{Quantified Linear Temporal Logic over Probabilistic Systems with an Application to Vacuity Checking}},
  booktitle =	{32nd International Conference on Concurrency Theory (CONCUR 2021)},
  pages =	{7:1--7:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-203-7},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{203},
  editor =	{Haddad, Serge and Varacca, Daniele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2021.7},
  URN =		{urn:nbn:de:0030-drops-143842},
  doi =		{10.4230/LIPIcs.CONCUR.2021.7},
  annote =	{Keywords: Quantified linear temporal logic, Markov chain, Markov decision process, vacuity}
}
Document
DOI: 10.4230/LIPIcs.CONCUR.2021.15
Guard Automata for the Verification of Safety and Liveness of Distributed Algorithms

Authors: Nathalie Bertrand, Bastien Thomas, and Josef Widder

Published in: LIPIcs, Volume 203, 32nd International Conference on Concurrency Theory (CONCUR 2021)

Abstract
Distributed algorithms typically run over arbitrary many processes and may involve unboundedly many rounds, making the automated verification of their correctness challenging. Building on domain theory, we introduce a framework that abstracts infinite-state distributed systems that represent distributed algorithms into finite-state guard automata. The soundness of the approach corresponds to the Scott-continuity of the abstraction, which relies on the assumption that the distributed algorithms are layered. Guard automata thus enable the verification of safety and liveness properties of distributed algorithms.
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Nathalie Bertrand, Bastien Thomas, and Josef Widder. Guard Automata for the Verification of Safety and Liveness of Distributed Algorithms. In 32nd International Conference on Concurrency Theory (CONCUR 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 203, pp. 15:1-15:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{bertrand_et_al:LIPIcs.CONCUR.2021.15,
  author =	{Bertrand, Nathalie and Thomas, Bastien and Widder, Josef},
  title =	{{Guard Automata for the Verification of Safety and Liveness of Distributed Algorithms}},
  booktitle =	{32nd International Conference on Concurrency Theory (CONCUR 2021)},
  pages =	{15:1--15:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-203-7},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{203},
  editor =	{Haddad, Serge and Varacca, Daniele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2021.15},
  URN =		{urn:nbn:de:0030-drops-143926},
  doi =		{10.4230/LIPIcs.CONCUR.2021.15},
  annote =	{Keywords: Verification, Distributed algorithms, Domain theory}
}
Document
DOI: 10.4230/LIPIcs.FSTTCS.2020.39
Synthesizing Safe Coalition Strategies

Authors: Nathalie Bertrand, Patricia Bouyer, and Anirban Majumdar

Published in: LIPIcs, Volume 182, 40th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2020)

Abstract
Concurrent games with a fixed number of agents have been thoroughly studied, with various solution concepts and objectives for the agents. In this paper, we consider concurrent games with an arbitrary number of agents, and study the problem of synthesizing a coalition strategy to achieve a global safety objective. The problem is non-trivial since the agents do not know a priori how many they are when they start the game. We prove that the existence of a safe arbitrary-large coalition strategy for safety objectives is a PSPACE-hard problem that can be decided in exponential space.
Cite as

Nathalie Bertrand, Patricia Bouyer, and Anirban Majumdar. Synthesizing Safe Coalition Strategies. In 40th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 182, pp. 39:1-39:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{bertrand_et_al:LIPIcs.FSTTCS.2020.39,
  author =	{Bertrand, Nathalie and Bouyer, Patricia and Majumdar, Anirban},
  title =	{{Synthesizing Safe Coalition Strategies}},
  booktitle =	{40th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2020)},
  pages =	{39:1--39:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-174-0},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{182},
  editor =	{Saxena, Nitin and Simon, Sunil},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2020.39},
  URN =		{urn:nbn:de:0030-drops-132807},
  doi =		{10.4230/LIPIcs.FSTTCS.2020.39},
  annote =	{Keywords: concurrent games, parameterized verification, strategy synthesis}
}
Document
DOI: 10.4230/LIPIcs.FSTTCS.2020.40
Dynamic Network Congestion Games

Authors: Nathalie Bertrand, Nicolas Markey, Suman Sadhukhan, and Ocan Sankur

Published in: LIPIcs, Volume 182, 40th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2020)

Abstract
Congestion games are a classical type of games studied in game theory, in which n players choose a resource, and their individual cost increases with the number of other players choosing the same resource. In network congestion games (NCGs), the resources correspond to simple paths in a graph, e.g. representing routing options from a source to a target. In this paper, we introduce a variant of NCGs, referred to as dynamic NCGs: in this setting, players take transitions synchronously, they select their next transitions dynamically, and they are charged a cost that depends on the number of players simultaneously using the same transition. We study, from a complexity perspective, standard concepts of game theory in dynamic NCGs: social optima, Nash equilibria, and subgame perfect equilibria. Our contributions are the following: the existence of a strategy profile with social cost bounded by a constant is in PSPACE and NP-hard. (Pure) Nash equilibria always exist in dynamic NCGs; the existence of a Nash equilibrium with bounded cost can be decided in EXPSPACE, and computing a witnessing strategy profile can be done in doubly-exponential time. The existence of a subgame perfect equilibrium with bounded cost can be decided in 2EXPSPACE, and a witnessing strategy profile can be computed in triply-exponential time.
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Nathalie Bertrand, Nicolas Markey, Suman Sadhukhan, and Ocan Sankur. Dynamic Network Congestion Games. In 40th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 182, pp. 40:1-40:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{bertrand_et_al:LIPIcs.FSTTCS.2020.40,
  author =	{Bertrand, Nathalie and Markey, Nicolas and Sadhukhan, Suman and Sankur, Ocan},
  title =	{{Dynamic Network Congestion Games}},
  booktitle =	{40th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2020)},
  pages =	{40:1--40:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-174-0},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{182},
  editor =	{Saxena, Nitin and Simon, Sunil},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2020.40},
  URN =		{urn:nbn:de:0030-drops-132811},
  doi =		{10.4230/LIPIcs.FSTTCS.2020.40},
  annote =	{Keywords: Congestion games, Nash equilibria, Subgame perfect equilibria, Complexity}
}
Document
Invited Talk
DOI: 10.4230/LIPIcs.MFCS.2020.1
Concurrent Games with Arbitrarily Many Players (Invited Talk)

Authors: Nathalie Bertrand

Published in: LIPIcs, Volume 170, 45th International Symposium on Mathematical Foundations of Computer Science (MFCS 2020)

Abstract
Traditional concurrent games on graphs involve a fixed number of players, who take decisions simultaneously, determining the next state of the game. With Anirban Majumdar and Patricia Bouyer, we introduced a parameterized variant of concurrent games on graphs, where the parameter is precisely the number of players. Parameterized concurrent games are described by finite graphs, in which the transitions bear finite-word languages to describe the possible move combinations that lead from one vertex to another. We report on results on two problems for such concurrent games with arbitrary many players. To start with, we studied the problem of determining whether the first player, say Eve, has a strategy to ensure a reachability objective against any strategy profile of her opponents as a coalition. In particular Eve’s strategy should be independent of the number of opponents she actually has. We establish the precise complexities of the problem for reachability objectives. Second, we considered a synthesis problem, where one aims at designing a strategy for each of the (arbitrarily many) players so as to achieve a common objective. For safety objectives, we show that this kind of distributed synthesis problem is decidable.
Cite as

Nathalie Bertrand. Concurrent Games with Arbitrarily Many Players (Invited Talk). In 45th International Symposium on Mathematical Foundations of Computer Science (MFCS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 170, pp. 1:1-1:8, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{bertrand:LIPIcs.MFCS.2020.1,
  author =	{Bertrand, Nathalie},
  title =	{{Concurrent Games with Arbitrarily Many Players}},
  booktitle =	{45th International Symposium on Mathematical Foundations of Computer Science (MFCS 2020)},
  pages =	{1:1--1:8},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-159-7},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{170},
  editor =	{Esparza, Javier and Kr\'{a}l', Daniel},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2020.1},
  URN =		{urn:nbn:de:0030-drops-126724},
  doi =		{10.4230/LIPIcs.MFCS.2020.1},
  annote =	{Keywords: concurrent games, parameterized verification}
}
Document
DOI: 10.4230/LIPIcs.FSTTCS.2019.31
Concurrent Parameterized Games

Authors: Nathalie Bertrand, Patricia Bouyer, and Anirban Majumdar

Published in: LIPIcs, Volume 150, 39th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2019)

Abstract
Traditional concurrent games on graphs involve a fixed number of players, who take decisions simultaneously, determining the next state of the game. In this paper, we introduce a parameterized variant of concurrent games on graphs, where the parameter is precisely the number of players. Parameterized concurrent games are described by finite graphs, in which the transitions bear regular languages to describe the possible move combinations that lead from one vertex to another. We consider the problem of determining whether the first player, say Eve, has a strategy to ensure a reachability objective against any strategy profile of her opponents as a coalition. In particular Eve’s strategy should be independent of the number of opponents she actually has. Technically, this paper focuses on an a priori simpler setting where the languages labeling transitions only constrain the number of opponents (but not their precise action choices). These constraints are described as semilinear sets, finite unions of intervals, or intervals. We establish the precise complexities of the parameterized reachability game problem, ranging from PTIME-complete to PSPACE-complete, in a variety of situations depending on the contraints (semilinear predicates, unions of intervals, or intervals) and on the presence or not of non-determinism.
Cite as

Nathalie Bertrand, Patricia Bouyer, and Anirban Majumdar. Concurrent Parameterized Games. In 39th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 150, pp. 31:1-31:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{bertrand_et_al:LIPIcs.FSTTCS.2019.31,
  author =	{Bertrand, Nathalie and Bouyer, Patricia and Majumdar, Anirban},
  title =	{{Concurrent Parameterized Games}},
  booktitle =	{39th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2019)},
  pages =	{31:1--31:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-131-3},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{150},
  editor =	{Chattopadhyay, Arkadev and Gastin, Paul},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2019.31},
  URN =		{urn:nbn:de:0030-drops-115931},
  doi =		{10.4230/LIPIcs.FSTTCS.2019.31},
  annote =	{Keywords: concurrent games, parameterized verification}
}
Document
DOI: 10.4230/LIPIcs.CONCUR.2019.32
Reconfiguration and Message Losses in Parameterized Broadcast Networks

Authors: Nathalie Bertrand, Patricia Bouyer, and Anirban Majumdar

Published in: LIPIcs, Volume 140, 30th International Conference on Concurrency Theory (CONCUR 2019)

Abstract
Broadcast networks allow one to model networks of identical nodes communicating through message broadcasts. Their parameterized verification aims at proving a property holds for any number of nodes, under any communication topology, and on all possible executions. We focus on the coverability problem which dually asks whether there exists an execution that visits a configuration exhibiting some given state of the broadcast protocol. Coverability is known to be undecidable for static networks, i.e. when the number of nodes and communication topology is fixed along executions. In contrast, it is decidable in PTIME when the communication topology may change arbitrarily along executions, that is for reconfigurable networks. Surprisingly, no lower nor upper bounds on the minimal number of nodes, or the minimal length of covering execution in reconfigurable networks, appear in the literature. In this paper we show tight bounds for cutoff and length, which happen to be linear and quadratic, respectively, in the number of states of the protocol. We also introduce an intermediary model with static communication topology and non-deterministic message losses upon sending. We show that the same tight bounds apply to lossy networks, although, reconfigurable executions may be linearly more succinct than lossy executions. Finally, we show NP-completeness for the natural optimisation problem associated with the cutoff.
Cite as

Nathalie Bertrand, Patricia Bouyer, and Anirban Majumdar. Reconfiguration and Message Losses in Parameterized Broadcast Networks. In 30th International Conference on Concurrency Theory (CONCUR 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 140, pp. 32:1-32:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{bertrand_et_al:LIPIcs.CONCUR.2019.32,
  author =	{Bertrand, Nathalie and Bouyer, Patricia and Majumdar, Anirban},
  title =	{{Reconfiguration and Message Losses in Parameterized Broadcast Networks}},
  booktitle =	{30th International Conference on Concurrency Theory (CONCUR 2019)},
  pages =	{32:1--32:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-121-4},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{140},
  editor =	{Fokkink, Wan and van Glabbeek, Rob},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2019.32},
  URN =		{urn:nbn:de:0030-drops-109345},
  doi =		{10.4230/LIPIcs.CONCUR.2019.32},
  annote =	{Keywords: model checking, parameterized verification, broadcast networks}
}
Document
DOI: 10.4230/LIPIcs.CONCUR.2019.33
Verification of Randomized Consensus Algorithms Under Round-Rigid Adversaries

Authors: Nathalie Bertrand, Igor Konnov, Marijana Lazić, and Josef Widder

Published in: LIPIcs, Volume 140, 30th International Conference on Concurrency Theory (CONCUR 2019)

Abstract
Randomized fault-tolerant distributed algorithms pose a number of challenges for automated verification: (i) parameterization in the number of processes and faults, (ii) randomized choices and probabilistic properties, and (iii) an unbounded number of asynchronous rounds. This combination makes verification hard. Challenge (i) was recently addressed in the framework of threshold automata. We extend threshold automata to model randomized consensus algorithms that perform an unbounded number of asynchronous rounds. For non-probabilistic properties, we show that it is necessary and sufficient to verify these properties under round-rigid schedules, that is, schedules where processes enter round r only after all processes finished round r-1. For almost-sure termination, we analyze these algorithms under round-rigid adversaries, that is, fair adversaries that only generate round-rigid schedules. This allows us to do compositional and inductive reasoning that reduces verification of the asynchronous multi-round algorithms to model checking of a one-round threshold automaton. We apply this framework and automatically verify the following classic algorithms: Ben-Or’s and Bracha’s seminal consensus algorithms for crashes and Byzantine faults, 2-set agreement for crash faults, and RS-Bosco for the Byzantine case.
Cite as

Nathalie Bertrand, Igor Konnov, Marijana Lazić, and Josef Widder. Verification of Randomized Consensus Algorithms Under Round-Rigid Adversaries. In 30th International Conference on Concurrency Theory (CONCUR 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 140, pp. 33:1-33:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{bertrand_et_al:LIPIcs.CONCUR.2019.33,
  author =	{Bertrand, Nathalie and Konnov, Igor and Lazi\'{c}, Marijana and Widder, Josef},
  title =	{{Verification of Randomized Consensus Algorithms Under Round-Rigid Adversaries}},
  booktitle =	{30th International Conference on Concurrency Theory (CONCUR 2019)},
  pages =	{33:1--33:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-121-4},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{140},
  editor =	{Fokkink, Wan and van Glabbeek, Rob},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2019.33},
  URN =		{urn:nbn:de:0030-drops-109358},
  doi =		{10.4230/LIPIcs.CONCUR.2019.33},
  annote =	{Keywords: threshold automata, counter systems, parameterized verification, randomized distributed algorithms, Byzantine faults}
}
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