63 Search Results for "Anceaume, Emmanuelle"

Volume

OASIcs, Volume 82

2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020)

Tokenomics 2020, October 26-27, 2020, Toulouse, France

Editors: Emmanuelle Anceaume, Christophe Bisière, Matthieu Bouvard, Quentin Bramas, and Catherine Casamatta

Volume

LIPIcs, Volume 46

19th International Conference on Principles of Distributed Systems (OPODIS 2015)

OPODIS 2015, December 14-17, 2015, Rennes, France

Editors: Emmanuelle Anceaume, Christian Cachin, and Maria Potop-Butucaru

Document
DOI: 10.4230/LIPIcs.ITCS.2026.74
Adversarially-Robust Gossip Algorithms for Approximate Quantile and Mean Computations

Authors: Bernhard Haeupler, Marc Kaufmann, Raghu Raman Ravi, and Ulysse Schaller

Published in: LIPIcs, Volume 362, 17th Innovations in Theoretical Computer Science Conference (ITCS 2026)

Abstract
This paper presents gossip algorithms for aggregation tasks that demonstrate both robustness to adversarial corruptions of any order of magnitude and optimality across a substantial range of these corruption levels. Gossip algorithms distribute information in a scalable and efficient way by having random pairs of nodes exchange small messages. Value aggregation problems are of particular interest in this setting, as they occur frequently in practice, and many elegant algorithms have been proposed for computing aggregates and statistics such as averages and quantiles. An important and well-studied advantage of gossip algorithms is their robustness to message delays, network churn, and unreliable message transmissions. However, these crucial robustness guarantees only hold if all nodes follow the protocol and no messages are corrupted. In this paper, we remedy this by providing a framework to model both adversarial participants and message corruptions in gossip-style communications by allowing an adversary to control a small fraction of the nodes or corrupt messages arbitrarily. Despite this very powerful and general corruption model, we show that robust gossip algorithms can be designed for many important aggregation problems. Our algorithms guarantee that almost all nodes converge to an approximately correct answer with optimal efficiency and essentially as fast as without corruptions. The design of adversarially-robust gossip algorithms poses completely new challenges. Despite this, our algorithms remain very simple variations of known non-robust algorithms with often only subtle changes to avoid non-compliant nodes gaining too much influence over outcomes. While our algorithms remain simple, their analysis is much more complex and often requires a completely different approach than the non-adversarial setting.
Cite as

Bernhard Haeupler, Marc Kaufmann, Raghu Raman Ravi, and Ulysse Schaller. Adversarially-Robust Gossip Algorithms for Approximate Quantile and Mean Computations. In 17th Innovations in Theoretical Computer Science Conference (ITCS 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 362, pp. 74:1-74:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{haeupler_et_al:LIPIcs.ITCS.2026.74,
  author =	{Haeupler, Bernhard and Kaufmann, Marc and Ravi, Raghu Raman and Schaller, Ulysse},
  title =	{{Adversarially-Robust Gossip Algorithms for Approximate Quantile and Mean Computations}},
  booktitle =	{17th Innovations in Theoretical Computer Science Conference (ITCS 2026)},
  pages =	{74:1--74:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-410-9},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{362},
  editor =	{Saraf, Shubhangi},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2026.74},
  URN =		{urn:nbn:de:0030-drops-253611},
  doi =		{10.4230/LIPIcs.ITCS.2026.74},
  annote =	{Keywords: Gossip Algorithms, Distributed Computing, Adversarial Robustness}
}
Document
DOI: 10.4230/LIPIcs.FSTTCS.2025.21
Overlay Network Construction: Improved Overall and Node-Wise Message Complexity

Authors: Yi-Jun Chang, Yanyu Chen, and Gopinath Mishra

Published in: LIPIcs, Volume 360, 45th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2025)

Abstract
We consider the problem of constructing distributed overlay networks, where nodes in a reconfigurable system can create or sever connections with nodes whose identifiers they know. Initially, each node knows only its own and its neighbors' identifiers, forming a local channel, while the evolving structure is termed the global channel. The goal is to reconfigure any connected graph into a desired topology, such as a bounded-degree expander graph or a well-formed tree (WFT) with a constant maximum degree and logarithmic diameter, minimizing the total number of rounds and message complexity. This problem mirrors real-world peer-to-peer network construction, where creating robust and efficient systems is desired. We study the overlay reconstruction problem in a network of n nodes in two models: GOSSIP-reply and HYBRID. In the GOSSIP-reply model, each node can send a message and receive a corresponding reply message in one round. In the HYBRID model, a node can send O(1) messages to each neighbor in the local channel and a total of O(log n) messages in the global channel. In both models, we propose protocols for WFT construction with O (n log n) message complexities using messages of O(log n) bits. In the GOSSIP-reply model, our protocol takes O(log n) rounds while in the HYBRID model, our protocol takes O(log² n) rounds. Both protocols use O (n log² n) bits of communication. We obtain improved bounds over prior work: GOSSIP-reply: A recent result by Dufoulon et al. (ITCS 2024) achieved O(log⁵ n) round complexity and O (n log⁵ n) message complexity using messages of at least Ω(log² n) bits in GOSSIP-reply. With messages of size O(log n), our protocol achieves an optimal round complexity of O(log n) and an improved message complexity of O(n log n). HYBRID: Götte et al. (Distributed Computing 2023) showed an optimal O(log n)-round algorithm with O(log² n) global messages per round which incurs a message complexity of Ω(m), where m is the number of edges in the initial topology. At the cost of increasing the round complexity to O(log² n) while using only O(log n) messages globally, our protocol achieves a message complexity that is independent of m. Our approach ensures that the total number of messages for node v, with degree deg(v) in the initial topology, is bounded by O(deg(v) + log n), while the algorithm of Götte et al. requires O(deg(v) + (log⁴ n)/(log log n)) messages per node.
Cite as

Yi-Jun Chang, Yanyu Chen, and Gopinath Mishra. Overlay Network Construction: Improved Overall and Node-Wise Message Complexity. In 45th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 360, pp. 21:1-21:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{chang_et_al:LIPIcs.FSTTCS.2025.21,
  author =	{Chang, Yi-Jun and Chen, Yanyu and Mishra, Gopinath},
  title =	{{Overlay Network Construction: Improved Overall and Node-Wise Message Complexity}},
  booktitle =	{45th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2025)},
  pages =	{21:1--21:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-406-2},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{360},
  editor =	{Aiswarya, C. and Mehta, Ruta and Roy, Subhajit},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2025.21},
  URN =		{urn:nbn:de:0030-drops-251025},
  doi =		{10.4230/LIPIcs.FSTTCS.2025.21},
  annote =	{Keywords: Distributed algorithms, Overlay networks, Expander graphs}
}
Document
DOI: 10.4230/LIPIcs.DISC.2025.26
Towards Constant Time Multi-Call Rumor Spreading on Small-Set Expanders

Authors: Emilio Cruciani, Sebastian Forster, and Tijn de Vos

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

Abstract
We study a multi-call variant of the classic PUSH&PULL rumor spreading process where nodes can contact k of their neighbors instead of a single one during both PUSH and PULL operations. We show that rumor spreading can be made faster at the cost of an increased amount of communication between the nodes. As a motivating example, consider the process on a complete graph of n nodes: while the standard PUSH&PULL protocol takes Θ(log n) rounds, we prove that our k-PUSH&PULL variant completes in Θ(log_{k} n) rounds, with high probability. We generalize this result in an expansion-sensitive way, as has been done for the classic PUSH&PULL protocol for different notions of expansion, e.g., conductance and vertex expansion. We consider small-set vertex expanders, graphs in which every sufficiently small subset of nodes has a large neighborhood, ensuring strong local connectivity. In particular, when the expansion parameter satisfies ϕ > 1, these graphs have a diameter of o(log n), as opposed to other standard notions of expansion. Since the graph’s diameter is a lower bound on the number of rounds required for rumor spreading, this makes small-set expanders particularly well-suited for fast information dissemination. We prove that k-PUSH&PULL takes O(log_{ϕ} n ⋅ log_{k} n) rounds in these expanders, with high probability. We complement this with a simple lower bound of Ω(log_{ϕ} n+ log_{k} n) rounds.
Cite as

Emilio Cruciani, Sebastian Forster, and Tijn de Vos. Towards Constant Time Multi-Call Rumor Spreading on Small-Set Expanders. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 26:1-26:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{cruciani_et_al:LIPIcs.DISC.2025.26,
  author =	{Cruciani, Emilio and Forster, Sebastian and de Vos, Tijn},
  title =	{{Towards Constant Time Multi-Call Rumor Spreading on Small-Set Expanders}},
  booktitle =	{39th International Symposium on Distributed Computing (DISC 2025)},
  pages =	{26:1--26:25},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-402-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{356},
  editor =	{Kowalski, Dariusz R.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.26},
  URN =		{urn:nbn:de:0030-drops-248434},
  doi =		{10.4230/LIPIcs.DISC.2025.26},
  annote =	{Keywords: small set expansion, vertex expansion, rumor spreading, multi-call rumor spreading, push\&pull protocol}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2025.60
Brief Announcement: Distributed Sparsest Cut via Eigenvalue Estimation

Authors: Yannic Maus and Tijn de Vos

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

Abstract
We give new, improved bounds for approximating the sparsest cut value or in other words the conductance ϕ of a graph in the CONGEST model. As our main result, we present an algorithm running in O(log² n/ϕ) rounds in which every vertex outputs a value ̃ ϕ satisfying ϕ ≤ ̃ ϕ ≤ √{2.01ϕ}. In most regimes, our algorithm improves significantly over the previously fastest algorithm for the problem [Chen, Meierhans, Probst Gutenberg, Saranurak; SODA 25]. Additionally, our result generalizes to k-way conductance. We obtain these results, by approximating the eigenvalues of the normalized Laplacian matrix L: = I-Deg^{-1/2}ADeg^ {-1/2}, where, A is the adjacency matrix and Deg is the diagonal matrix with the weighted degrees on the diagonal. We show our algorithms are near-optimal by proving a lower bound for computing the smallest non-trivial eigenvalue of L, even in the stronger LOCAL model The previous state of the art sparsest cut algorithm is in the technical realm of expander decompositions. Our algorithms, on the other hand, are relatively simple and easy to implement. At the core, they rely on the well-known power method, which comes down to repeatedly multiplying the Laplacian with a vector. This operation can be performed in a single round in the CONGEST model. All our algorithms apply to weighted, undirected graphs. Our lower bounds apply even in unweighted graphs.
Cite as

Yannic Maus and Tijn de Vos. Brief Announcement: Distributed Sparsest Cut via Eigenvalue Estimation. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 60:1-60:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{maus_et_al:LIPIcs.DISC.2025.60,
  author =	{Maus, Yannic and de Vos, Tijn},
  title =	{{Brief Announcement: Distributed Sparsest Cut via Eigenvalue Estimation}},
  booktitle =	{39th International Symposium on Distributed Computing (DISC 2025)},
  pages =	{60:1--60:7},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-402-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{356},
  editor =	{Kowalski, Dariusz R.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.60},
  URN =		{urn:nbn:de:0030-drops-248763},
  doi =		{10.4230/LIPIcs.DISC.2025.60},
  annote =	{Keywords: CONGEST, Sparsest Cut, Laplacian, Eigenvalues, Spectral Graph Theory}
}
Document
DOI: 10.4230/LIPIcs.AFT.2025.3
Fast, Private and Regulated Payments in Asynchronous Networks

Authors: Maxence Brugeres, Victor Languille, Petr Kuznetsov, and Hamza Zarfaoui

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

Abstract
We propose a decentralized asset-transfer system that enjoys full privacy: no party can learn the details of a transaction, except for its issuer and its recipient. Furthermore, the recipient is not aware of the sender’s identity. Our system does not rely on consensus or synchrony assumptions, and therefore, it is responsive, since it runs at the actual network speed. Under the hood, every transaction creates a consumable coin equipped with a non-interactive zero-knowledge proof (NIZK) that confirms that the issuer has sufficient funds without revealing any information about her identity, the recipient’s identity, or the payment amount. Moreover, we equip our system with a regulatory enforcement mechanism that can be used to regulate transfer limits or restrict specific addresses from sending or receiving funds, while preserving the system’s privacy guarantees. Finally, we report on PaxPay, our implementation of Fully Private Asset Transfer (FPAT) that uses the Gnark library for the NIZKs. In our benchmark, PaxPay exhibits better performance than earlier proposals that either ensure only partial privacy, require some kind of network synchrony or do not implement regulation features. Our system thus reconciles privacy, responsiveness, regulation enforcement and performance.
Cite as

Maxence Brugeres, Victor Languille, Petr Kuznetsov, and Hamza Zarfaoui. Fast, Private and Regulated Payments in Asynchronous Networks. In 7th Conference on Advances in Financial Technologies (AFT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 354, pp. 3:1-3:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{brugeres_et_al:LIPIcs.AFT.2025.3,
  author =	{Brugeres, Maxence and Languille, Victor and Kuznetsov, Petr and Zarfaoui, Hamza},
  title =	{{Fast, Private and Regulated Payments in Asynchronous Networks}},
  booktitle =	{7th Conference on Advances in Financial Technologies (AFT 2025)},
  pages =	{3:1--3:24},
  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.2025.3},
  URN =		{urn:nbn:de:0030-drops-247227},
  doi =		{10.4230/LIPIcs.AFT.2025.3},
  annote =	{Keywords: Anonymous, Asset Transfer, Asynchronous System, BFT, CBDC, NIZK, Payment System, Privacy, Regulation, Scalability, zk-SNARK}
}
Document
DOI: 10.4230/OASIcs.FMBC.2025.10
Program Logics for Ledgers

Authors: Orestis Melkonian, Wouter Swierstra, and James Chapman

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

Abstract
Distributed ledgers nowadays manage substantial monetary funds in the form of cryptocurrencies such as Bitcoin, Ethereum, and Cardano. For such ledgers to be safe, operations that add new entries must be cryptographically sound - but it is less clear how to reason effectively about such ever-growing linear data structures. This paper demonstrates how distributed ledgers may be viewed as computer programs, that, when executed, transfer funds between various parties. As a result, familiar program logics, such as Hoare logic, are applied in a novel setting. Borrowing ideas from concurrent separation logic, this enables modular reasoning principles over arbitrary fragments of any ledger. All of our results have been mechanised in the Agda proof assistant.
Cite as

Orestis Melkonian, Wouter Swierstra, and James Chapman. Program Logics for Ledgers. In 6th International Workshop on Formal Methods for Blockchains (FMBC 2025). Open Access Series in Informatics (OASIcs), Volume 129, pp. 10:1-10:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{melkonian_et_al:OASIcs.FMBC.2025.10,
  author =	{Melkonian, Orestis and Swierstra, Wouter and Chapman, James},
  title =	{{Program Logics for Ledgers}},
  booktitle =	{6th International Workshop on Formal Methods for Blockchains (FMBC 2025)},
  pages =	{10:1--10:22},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-371-3},
  ISSN =	{2190-6807},
  year =	{2025},
  volume =	{129},
  editor =	{Marmsoler, Diego and Xu, Meng},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.FMBC.2025.10},
  URN =		{urn:nbn:de:0030-drops-230370},
  doi =		{10.4230/OASIcs.FMBC.2025.10},
  annote =	{Keywords: blockchain, distributed ledgers, UTxO separation logic, program semantics, formal verification, Agda}
}
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)

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@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
DOI: 10.4230/LIPIcs.OPODIS.2021.6
On Finality in Blockchains

Authors: Emmanuelle Anceaume, Antonella Del Pozzo, Thibault Rieutord, and Sara Tucci-Piergiovanni

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

Abstract
This paper focuses on blockchain finality, which refers to the time when it becomes impossible to remove a block that has previously been appended to the blockchain. Blockchain finality can be deterministic or probabilistic, immediate or eventual. To favor availability against consistency in the face of partitions, most blockchains only offer probabilistic eventual finality: blocks may be revoked after being appended to the blockchain, yet with decreasing probability as they sink deeper into the chain. Other blockchains favor consistency by leveraging the immediate finality of Consensus - a block appended is never revoked - at the cost of additional synchronization. The quest for "good" deterministic finality properties for blockchains is still in its infancy, though. Our motivation is to provide a thorough study of several possible deterministic finality properties and explore their solvability. This is achieved by introducing the notion of bounded revocation, which informally says that the number of blocks that can be revoked from the current blockchain is bounded. Based on the requirements we impose on this revocation number, we provide reductions between different forms of eventual finality, Consensus and Eventual Consensus. From these reductions, we show some related impossibility results in presence of Byzantine processes, and provide non-trivial results. In particular, we provide an algorithm that solves a weak form of eventual finality in an asynchronous system in presence of an unbounded number of Byzantine processes. We also provide an algorithm that solves eventual finality with a bounded revocation number in an eventually synchronous environment in presence of less than half of Byzantine processes. The simplicity of the arguments should better guide blockchain designs and link them to clear formal properties of finality.
Cite as

Emmanuelle Anceaume, Antonella Del Pozzo, Thibault Rieutord, and Sara Tucci-Piergiovanni. On Finality in Blockchains. In 25th International Conference on Principles of Distributed Systems (OPODIS 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 217, pp. 6:1-6:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{anceaume_et_al:LIPIcs.OPODIS.2021.6,
  author =	{Anceaume, Emmanuelle and Del Pozzo, Antonella and Rieutord, Thibault and Tucci-Piergiovanni, Sara},
  title =	{{On Finality in Blockchains}},
  booktitle =	{25th International Conference on Principles of Distributed Systems (OPODIS 2021)},
  pages =	{6:1--6:19},
  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.2021.6},
  URN =		{urn:nbn:de:0030-drops-157810},
  doi =		{10.4230/LIPIcs.OPODIS.2021.6},
  annote =	{Keywords: Blockchain, consistency properties, Byzantine tolerant implementations}
}
Document
Complete Volume
DOI: 10.4230/OASIcs.Tokenomics.2020
OASIcs, Volume 82, Tokenomics 2020, Complete Volume

Authors: Emmanuelle Anceaume, Christophe Bisière, Matthieu Bouvard, Quentin Bramas, and Catherine Casamatta

Published in: OASIcs, Volume 82, 2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020)

Abstract
OASIcs, Volume 82, Tokenomics 2020, Complete Volume
Cite as

2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020). Open Access Series in Informatics (OASIcs), Volume 82, pp. 1-136, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@Proceedings{anceaume_et_al:OASIcs.Tokenomics.2020,
  title =	{{OASIcs, Volume 82, Tokenomics 2020, Complete Volume}},
  booktitle =	{2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020)},
  pages =	{1--136},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-157-3},
  ISSN =	{2190-6807},
  year =	{2021},
  volume =	{82},
  editor =	{Anceaume, Emmanuelle and Bisi\`{e}re, Christophe and Bouvard, Matthieu and Bramas, Quentin and Casamatta, Catherine},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.Tokenomics.2020},
  URN =		{urn:nbn:de:0030-drops-135213},
  doi =		{10.4230/OASIcs.Tokenomics.2020},
  annote =	{Keywords: OASIcs, Volume 82, Tokenomics 2020, Complete Volume}
}
Document
Front Matter
DOI: 10.4230/OASIcs.Tokenomics.2020.0
Front Matter, Table of Contents, Preface, Conference Organization

Authors: Emmanuelle Anceaume, Christophe Bisière, Matthieu Bouvard, Quentin Bramas, and Catherine Casamatta

Published in: OASIcs, Volume 82, 2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020)

Abstract
Front Matter, Table of Contents, Preface, Conference Organization
Cite as

2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020). Open Access Series in Informatics (OASIcs), Volume 82, pp. 0:i-0:x, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{anceaume_et_al:OASIcs.Tokenomics.2020.0,
  author =	{Anceaume, Emmanuelle and Bisi\`{e}re, Christophe and Bouvard, Matthieu and Bramas, Quentin and Casamatta, Catherine},
  title =	{{Front Matter, Table of Contents, Preface, Conference Organization}},
  booktitle =	{2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020)},
  pages =	{0:i--0:x},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-157-3},
  ISSN =	{2190-6807},
  year =	{2021},
  volume =	{82},
  editor =	{Anceaume, Emmanuelle and Bisi\`{e}re, Christophe and Bouvard, Matthieu and Bramas, Quentin and Casamatta, Catherine},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.Tokenomics.2020.0},
  URN =		{urn:nbn:de:0030-drops-135220},
  doi =		{10.4230/OASIcs.Tokenomics.2020.0},
  annote =	{Keywords: Front Matter, Table of Contents, Preface, Conference Organization}
}
Document
Invited Talk
DOI: 10.4230/OASIcs.Tokenomics.2020.1
Some Economics of Fintech (Invited Talk)

Authors: Jean Tirole

Published in: OASIcs, Volume 82, 2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020)

Abstract
The contours of digital payments are still in the making. Recent years have seen the emergence of new instruments best exemplified by public cryptocurrencies like Bitcoin or Big Tech payment systems like Alipay. These developments in the private sector have in turn fueled discussions and projects around the creation of central bank digital currencies. Digital currencies have a lot to offer. They can provide consumers with user-friendly low-cost means of payment and facilitate the integration of payment systems across borders. They may also offer alternatives in countries with dysfunctional national monetary systems. On the supply side, private digital currencies can be a source of funding (e.g., initial coin offerings) and allow businesses to retain consumers and to collect information. Which form of digital currency will eventually prevail has yet to be seen. Popular permissionless cryptocurrencies lack in their current form the price stability necessary to serve as a store of value: accepting a payment in Bitcoin exposes a merchant to costly financial risk. Stable coins pegged to a central-bank currency and backed by safe collateral are an attempt to dim excess volatility (e.g., Tether or Libra). But this guarantee creates new challenges: collateral must be segregated and prudentially supervised to ensure consumer protection. It is unclear which authority would have the capacity and incentives to provide that supervision for a global digital currency. More generally, a private global digital currency would raise a range of public policy issues ranging from tax fraud and money laundering control, to loss of seignorage revenue, impediments to monetary policy and potential threat to financial stability. In that context, Central Bank Digital Currencies (CBDC) may provide a solution that combines the convenience of private digital money with the institutional support of a state. But the scope of a CBDC’s deployment needs to be carefully calibrated: a CBDC directly held by wholesale or retail depositors would compete with bank deposits, possibly limiting banks’ ability to engage in their essential function of maturity transformation through long-term credit. Overall, the deployment of new technologies for payments has the potential to create meaningful value for consumers. However, technological disruption does not upend the fundamental economic principles that have shaped our financial systems and its regulatory framework. Applying these principles may be our best chance to understand the ongoing Fintech revolution.
Cite as

Jean Tirole. Some Economics of Fintech (Invited Talk). In 2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020). Open Access Series in Informatics (OASIcs), Volume 82, p. 1:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{tirole:OASIcs.Tokenomics.2020.1,
  author =	{Tirole, Jean},
  title =	{{Some Economics of Fintech}},
  booktitle =	{2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020)},
  pages =	{1:1--1:1},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-157-3},
  ISSN =	{2190-6807},
  year =	{2021},
  volume =	{82},
  editor =	{Anceaume, Emmanuelle and Bisi\`{e}re, Christophe and Bouvard, Matthieu and Bramas, Quentin and Casamatta, Catherine},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.Tokenomics.2020.1},
  URN =		{urn:nbn:de:0030-drops-135239},
  doi =		{10.4230/OASIcs.Tokenomics.2020.1},
  annote =	{Keywords: Cryptocurrency, Stable Coin, Central Bank Digital Currency, Fintech, Financial Regulation}
}
Document
Invited Talk
DOI: 10.4230/OASIcs.Tokenomics.2020.2
When Nakamoto Meets Nash: Blockchain Breakthrough Through the Lens of Game Theory (Invited Talk)

Authors: Ittai Abraham

Published in: OASIcs, Volume 82, 2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020)

Abstract
We discuss the deep connections between Blockchain Technology, Computer Science and Economics. The talk surveys the ways the Blockchain disruption raises fundamental challenges that have a deep game theoretic nature. We focus on four major open questions: 1) The need for a game theoretic endogenous theory of the utility of Money Systems that can model friction, fairness, and trust. 2) The need to incentivize trust in both consensus and execution. A need for a game theoretic theory of Consensus and analogue to Byzantine Fault Tolerance. A need for a game theoretic framework for scalable validation. 3) The challenge of incentivizing fairness and chain quality. Can we use notions of robust equilibrium to provide better notions of fairness? 4) The open question of how Blockchains can incentivise welfare. The need for a theory of Blockchains as public goods.
Cite as

Ittai Abraham. When Nakamoto Meets Nash: Blockchain Breakthrough Through the Lens of Game Theory (Invited Talk). In 2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020). Open Access Series in Informatics (OASIcs), Volume 82, p. 2:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{abraham:OASIcs.Tokenomics.2020.2,
  author =	{Abraham, Ittai},
  title =	{{When Nakamoto Meets Nash: Blockchain Breakthrough Through the Lens of Game Theory}},
  booktitle =	{2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020)},
  pages =	{2:1--2:1},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-157-3},
  ISSN =	{2190-6807},
  year =	{2021},
  volume =	{82},
  editor =	{Anceaume, Emmanuelle and Bisi\`{e}re, Christophe and Bouvard, Matthieu and Bramas, Quentin and Casamatta, Catherine},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.Tokenomics.2020.2},
  URN =		{urn:nbn:de:0030-drops-135248},
  doi =		{10.4230/OASIcs.Tokenomics.2020.2},
  annote =	{Keywords: Game theory, Consensus, Blockchain}
}
Document
Invited Talk
DOI: 10.4230/OASIcs.Tokenomics.2020.3
Digital Currencies as Types (Invited Talk)

Authors: Timothy A. K. Zakian

Published in: OASIcs, Volume 82, 2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020)

Abstract
Linear types have been well studied since their inception by Girard; a linear value can be moved from one place to another, but can never be copied or forgotten. From its inception Move - a new programming language developed to implement custom transactions and smart contracts on the Libra Blockchain - has had values-or resources-that behave in this linear manner as a central part of its semantics. On the Libra Blockchain, Move enables significant parts of the Libra protocol, including the Libra Coins, transaction processing, and validator management. In this talk, we will look at how different digital assets are represented with Move on the Libra Blockchain. In the process of exploring the representation of digital assets on-chain in Move, we will revisit one of the first examples used in the paper that introduced linear logic; that of payments, and encounter other ideas from programming languages along the way, such as type-indexed data types and code modularity. We will see how we can leverage these ideas to provide strong guarantees of key asset properties such as losslessness, value conservation, and explicit representation of an asset, its currency, and its value. As we explore the implementation of a digital asset in Move, we will see how, in Move, code is organized into a number of different modules, with each module consisting of resources and functions that can be used with the resources defined in that module. This gives rise to a type of strong encapsulation around the resources defined within a Move module: only functions within the module that define the resource can create, destroy, or access the fields of that resource. We will see how representing a digital asset as a resource, coupled with this strong encapsulation, and privileging the creation and destruction operations within the module means that we can build a digital asset representation on-chain that is lossless by design: wherever it may go on-chain, such a digital asset cannot ever be "lost" or accidentally forgotten, and, no new digital assets can be created on-chain without the correct privileges. We can then index this digital asset resource that we’ve built in Move by a type-level representation of each currency in the system to arrive at an explicit static representation of the currency of a digital asset. This representation statically disallows entire classes of possible issues, such as trying to combine two assets in different currencies, while still preserving all of the properties that we previously had, such as losslessness. With this representation of a digital asset that we have built in Move, we can also test and verify that the value of the digital assets on-chain are preserved outside of creation and destruction operations; since the only functions that can change the value of an asset must be defined within the same module we can heavily test, and in fact verify, that these functions preserve the value of any digital assets that they may interact with. At the end of this process we arrive at a testable, verifiable, and explicit representation of a digital asset in Move that is lossless, conserves value, and represents its currency and value explicitly.
Cite as

Timothy A. K. Zakian. Digital Currencies as Types (Invited Talk). In 2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020). Open Access Series in Informatics (OASIcs), Volume 82, p. 3:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{zakian:OASIcs.Tokenomics.2020.3,
  author =	{Zakian, Timothy A. K.},
  title =	{{Digital Currencies as Types}},
  booktitle =	{2nd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2020)},
  pages =	{3:1--3:1},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-157-3},
  ISSN =	{2190-6807},
  year =	{2021},
  volume =	{82},
  editor =	{Anceaume, Emmanuelle and Bisi\`{e}re, Christophe and Bouvard, Matthieu and Bramas, Quentin and Casamatta, Catherine},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.Tokenomics.2020.3},
  URN =		{urn:nbn:de:0030-drops-135257},
  doi =		{10.4230/OASIcs.Tokenomics.2020.3},
  annote =	{Keywords: Digital Currencies, Linear Types, Move, Blockchains}
}
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