7 Search Results for "Azouvi, Sarah"

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

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

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

Abstract
We propose a novel relaxation of the classic asynchronous network model, called the random asynchronous model, which removes adversarial message scheduling while preserving unbounded message delays and Byzantine faults. Instead of an adversary dictating message order, delivery follows a random schedule. We analyze Byzantine consensus at different resilience thresholds (n = 3f+1, n = 2f+1, and n = f+2) and show that our relaxation allows consensus with probabilistic guarantees which are impossible in the standard asynchronous model or even the partially synchronous model. We complement these protocols with corresponding impossibility results, establishing the limits of consensus in the random asynchronous model.
Cite as

George Danezis, Jovan Komatovic, Lefteris Kokoris-Kogias, Alberto Sonnino, and Igor Zablotchi. Byzantine Consensus in the Random Asynchronous Model. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 28:1-28:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{danezis_et_al:LIPIcs.DISC.2025.28,
  author =	{Danezis, George and Komatovic, Jovan and Kokoris-Kogias, Lefteris and Sonnino, Alberto and Zablotchi, Igor},
  title =	{{Byzantine Consensus in the Random Asynchronous Model}},
  booktitle =	{39th International Symposium on Distributed Computing (DISC 2025)},
  pages =	{28:1--28:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-402-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{356},
  editor =	{Kowalski, Dariusz R.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.28},
  URN =		{urn:nbn:de:0030-drops-248457},
  doi =		{10.4230/LIPIcs.DISC.2025.28},
  annote =	{Keywords: network model, asynchronous, random scheduler, Byzantine consensus}
}
Document
DOI: 10.4230/LIPIcs.AFT.2025.16
Nakamoto Consensus from Multiple Resources

Authors: Mirza Ahad Baig, Christoph U. Günther, and Krzysztof Pietrzak

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

Abstract
The blocks in the Bitcoin blockchain "record" the amount of work W that went into creating them through proofs of work. When honest parties control a majority of the work, consensus is achieved by picking the chain with the highest recorded weight. Resources other than work have been considered to secure such longest-chain blockchains. In Chia, blocks record the amount of disk-space S (via a proof of space) and sequential computational steps V (through a VDF). In this paper, we ask what weight functions Γ(S,V,W) (that assign a weight to a block as a function of the recorded space, speed, and work) are secure in the sense that whenever the weight of the resources controlled by honest parties is larger than the weight of adversarial parties, the blockchain is secure against private double-spending attacks. We completely classify such functions in an idealized "continuous" model: Γ(S,V,W) is secure against private double-spending attacks if and only if it is homogeneous of degree one in the "timed" resources V and W, i.e., αΓ(S,V,W) = Γ(S,α V, α W). This includes the Bitcoin rule Γ(S,V,W) = W and the Chia rule Γ(S,V,W) = S ⋅ V. In a more realistic model where blocks are created at discrete time-points, one additionally needs some mild assumptions on the dependency on S (basically, the weight should not grow too much if S is slightly increased, say linear as in Chia). Our classification is more general and allows various instantiations of the same resource. It provides a powerful tool for designing new longest-chain blockchains. E.g., consider combining different PoWs to counter centralization, say the Bitcoin PoW W₁ and a memory-hard PoW W₂. Previous work suggested to use W₁+W₂ as weight. Our results show that using e.g., √{W₁}⋅ √{W₂} or min{W₁,W₂} are also secure, and we argue that in practice these are much better choices.
Cite as

Mirza Ahad Baig, Christoph U. Günther, and Krzysztof Pietrzak. Nakamoto Consensus from Multiple Resources. In 7th Conference on Advances in Financial Technologies (AFT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 354, pp. 16:1-16:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{baig_et_al:LIPIcs.AFT.2025.16,
  author =	{Baig, Mirza Ahad and G\"{u}nther, Christoph U. and Pietrzak, Krzysztof},
  title =	{{Nakamoto Consensus from Multiple Resources}},
  booktitle =	{7th Conference on Advances in Financial Technologies (AFT 2025)},
  pages =	{16:1--16:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-400-0},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{354},
  editor =	{Avarikioti, Zeta and Christin, Nicolas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2025.16},
  URN =		{urn:nbn:de:0030-drops-247353},
  doi =		{10.4230/LIPIcs.AFT.2025.16},
  annote =	{Keywords: Nakamoto Consensus, Heaviest-chain Rule, Resource Theory}
}
Document
DOI: 10.4230/LIPIcs.AFT.2025.21
Pool Formation in Oceanic Games: Shapley Value and Proportional Sharing

Authors: Aggelos Kiayias, Elias Koutsoupias, Evangelos Markakis, and Panagiotis Tsamopoulos

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

Abstract
We study a game-theoretic model for pool formation in Proof of Stake blockchain protocols. In such systems, stakeholders can form pools as a means of obtaining regular rewards from participation in ledger maintenance, with the power of each pool being dependent on its collective stake. The question we are interested in is the design of mechanisms, i.e., "reward sharing schemes," that suitably split rewards among pool members and achieve favorable properties in the resulting pool configuration. With this in mind, we initiate a non-cooperative game-theoretic analysis of the well known Shapley value scheme from cooperative game theory into the context of blockchains. In particular, we focus on the oceanic model of games, proposed by Milnor and Shapley (1978), which is suitable for populations where a small set of large players coexists with a big mass of rather small, negligible players. This provides an appropriate level of abstraction for pool formation processes that occur among the stakeholders of a blockchain. We provide comparisons between the Shapley mechanism and the more standard proportional scheme, in terms of attained decentralization, via a Price of Stability analysis and in terms of susceptibility to Sybil attacks, i.e., the strategic splitting of a players' stake with the intention of participating in multiple pools for increased profit. Interestingly, while the widely deployed proportional scheme appears to have certain advantages, the Shapley value scheme, which rewards higher the most pivotal players, emerges as a competitive alternative, by being able to bypass some of the downsides of proportional sharing in terms of Sybil attack susceptibility, while also not being far from optimal guarantees w.r.t. decentralization. Finally, we also complement our study with some variations of proportional sharing, where the profit is split in proportion to a superadditive or a subadditive function of the stake, showing that our results for the Shapley value scheme are maintained in comparison to these functions as well.
Cite as

Aggelos Kiayias, Elias Koutsoupias, Evangelos Markakis, and Panagiotis Tsamopoulos. Pool Formation in Oceanic Games: Shapley Value and Proportional Sharing. In 7th Conference on Advances in Financial Technologies (AFT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 354, pp. 21:1-21:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{kiayias_et_al:LIPIcs.AFT.2025.21,
  author =	{Kiayias, Aggelos and Koutsoupias, Elias and Markakis, Evangelos and Tsamopoulos, Panagiotis},
  title =	{{Pool Formation in Oceanic Games: Shapley Value and Proportional Sharing}},
  booktitle =	{7th Conference on Advances in Financial Technologies (AFT 2025)},
  pages =	{21:1--21:24},
  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.2025.21},
  URN =		{urn:nbn:de:0030-drops-247409},
  doi =		{10.4230/LIPIcs.AFT.2025.21},
  annote =	{Keywords: Shapley value, Nash equilibria, Price of Stability, Reward sharing schemes, Proof of Stake blockchains}
}
Document
DOI: 10.4230/LIPIcs.AFT.2025.23
Transaction Fee Market Design for Parallel Execution

Authors: Bahar Acilan, Andrei Constantinescu, Lioba Heimbach, and Roger Wattenhofer

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

Abstract
Given the low throughput of blockchains like Bitcoin and Ethereum, scalability - the ability to process an increasing number of transactions - has become a central focus of blockchain research. One promising approach is the parallelization of transaction execution across multiple threads. However, achieving efficient parallelization requires a redesign of the incentive structure within the fee market. Currently, the fee market does not differentiate between transactions that access multiple high-demand storage keys (i.e., unique identifiers for individual data entries) versus a single low-demand one, as long as they require the same computational effort. Addressing this discrepancy is crucial for enabling more effective parallel execution. In this work, we aim to bridge the gap between the current fee market and the need for parallel execution by exploring alternative fee market designs. To this end, we propose a framework consisting of two key components: a Gas Computation Mechanism (GCM), which quantifies the load a transaction places on the network in terms of parallelization and computation, measured in units of gas, and a Transaction Fee Mechanism (TFM), which assigns a price to each unit of gas. We additionally introduce a set of desirable properties for a GCM, propose several candidate mechanisms, and evaluate them against these criteria. Our analysis highlights two strong candidates: the weighted area GCM, which integrates smoothly with existing TFMs such as EIP‑1559 and satisfies a broad subset of the outlined properties, and the time-proportional makespan GCM, which assigns gas costs based on the context of the entire block’s schedule and, through this dependence on the overall execution outcome, captures the dynamics of parallel execution more accurately.
Cite as

Bahar Acilan, Andrei Constantinescu, Lioba Heimbach, and Roger Wattenhofer. Transaction Fee Market Design for Parallel Execution. In 7th Conference on Advances in Financial Technologies (AFT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 354, pp. 23:1-23:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{acilan_et_al:LIPIcs.AFT.2025.23,
  author =	{Acilan, Bahar and Constantinescu, Andrei and Heimbach, Lioba and Wattenhofer, Roger},
  title =	{{Transaction Fee Market Design for Parallel Execution}},
  booktitle =	{7th Conference on Advances in Financial Technologies (AFT 2025)},
  pages =	{23:1--23:25},
  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.2025.23},
  URN =		{urn:nbn:de:0030-drops-247426},
  doi =		{10.4230/LIPIcs.AFT.2025.23},
  annote =	{Keywords: blockchain, transaction fee mechanism, parallel execution}
}
Document
DOI: 10.4230/LIPIcs.AFT.2023.5
Security Analysis of Filecoin’s Expected Consensus in the Byzantine vs Honest Model

Authors: Xuechao Wang, Sarah Azouvi, and Marko Vukolić

Published in: LIPIcs, Volume 282, 5th Conference on Advances in Financial Technologies (AFT 2023)

Abstract
Filecoin is the largest storage-based open-source blockchain, both by storage capacity (>11EiB) and market capitalization. This paper provides the first formal security analysis of Filecoin’s consensus (ordering) protocol, Expected Consensus (EC). Specifically, we show that EC is secure against an arbitrary adversary that controls a fraction β of the total storage for β m < 1- e^{-(1-β)m}, where m is a parameter that corresponds to the expected number of blocks per round, currently m = 5 in Filecoin. We then present an attack, the n-split attack, where an adversary splits the honest miners between multiple chains, and show that it is successful for β m ≥ 1- e^{-(1-β)m}, thus proving that β m = 1- e^{-(1-β)m} is the tight security threshold of EC. This corresponds roughly to an adversary with 20% of the total storage pledged to the chain. Finally, we propose two improvements to EC security that would increase this threshold. One of these two fixes is being implemented as a Filecoin Improvement Proposal (FIP).
Cite as

Xuechao Wang, Sarah Azouvi, and Marko Vukolić. Security Analysis of Filecoin’s Expected Consensus in the Byzantine vs Honest Model. In 5th Conference on Advances in Financial Technologies (AFT 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 282, pp. 5:1-5:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{wang_et_al:LIPIcs.AFT.2023.5,
  author =	{Wang, Xuechao and Azouvi, Sarah and Vukoli\'{c}, Marko},
  title =	{{Security Analysis of Filecoin’s Expected Consensus in the Byzantine vs Honest Model}},
  booktitle =	{5th Conference on Advances in Financial Technologies (AFT 2023)},
  pages =	{5:1--5:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-303-4},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{282},
  editor =	{Bonneau, Joseph and Weinberg, S. Matthew},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2023.5},
  URN =		{urn:nbn:de:0030-drops-191943},
  doi =		{10.4230/LIPIcs.AFT.2023.5},
  annote =	{Keywords: Decentralized storage, Consensus, Security analysis}
}
Document
DOI: 10.4230/LIPIcs.DISC.2023.6
Base Fee Manipulation in Ethereum’s EIP-1559 Transaction Fee Mechanism

Authors: Sarah Azouvi, Guy Goren, Lioba Heimbach, and Alexander Hicks

Published in: LIPIcs, Volume 281, 37th International Symposium on Distributed Computing (DISC 2023)

Abstract
In 2021 Ethereum adjusted the transaction pricing mechanism by implementing EIP-1559, which introduces the base fee - a network fee that is burned and dynamically adjusts to the network demand. The authors of the Ethereum Improvement Proposal (EIP) noted that a miner with more than 50% of the mining power could be incentivized to deviate from the honest mining strategy. Instead, such a miner could propose a series of empty blocks to artificially lower demand and increase her future rewards. In this paper, we generalize this attack and show that under rational player behavior, deviating from the honest strategy can be profitable for a miner with less than 50% of the mining power. We show that even when miners do not collaborate, it is at times rational for smaller miners to join the attack. Finally, we propose a mitigation to address the identified vulnerability.
Cite as

Sarah Azouvi, Guy Goren, Lioba Heimbach, and Alexander Hicks. Base Fee Manipulation in Ethereum’s EIP-1559 Transaction Fee Mechanism. In 37th International Symposium on Distributed Computing (DISC 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 281, pp. 6:1-6:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{azouvi_et_al:LIPIcs.DISC.2023.6,
  author =	{Azouvi, Sarah and Goren, Guy and Heimbach, Lioba and Hicks, Alexander},
  title =	{{Base Fee Manipulation in Ethereum’s EIP-1559 Transaction Fee Mechanism}},
  booktitle =	{37th International Symposium on Distributed Computing (DISC 2023)},
  pages =	{6:1--6:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-301-0},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{281},
  editor =	{Oshman, Rotem},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2023.6},
  URN =		{urn:nbn:de:0030-drops-191325},
  doi =		{10.4230/LIPIcs.DISC.2023.6},
  annote =	{Keywords: blockchain, Ethereum, transaction fee mechanism, EIP-1559}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2022.19
Modeling Resources in Permissionless Longest-Chain Total-Order Broadcast

Authors: Sarah Azouvi, Christian Cachin, Duc V. Le, Marko Vukolić, and Luca Zanolini

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

Abstract
Blockchain protocols implement total-order broadcast in a permissionless setting, where processes can freely join and leave. In such a setting, to safeguard against Sybil attacks, correct processes rely on cryptographic proofs tied to a particular type of resource to make them eligible to order transactions. For example, in the case of Proof-of-Work (PoW), this resource is computation, and the proof is a solution to a computationally hard puzzle. Conversely, in Proof-of-Stake (PoS), the resource corresponds to the number of coins that every process in the system owns, and a secure lottery selects a process for participation proportionally to its coin holdings. Although many resource-based blockchain protocols are formally proven secure in the literature, the existing security proofs fail to demonstrate why particular types of resources cause the blockchain protocols to be vulnerable to distinct classes of attacks. For instance, PoS systems are more vulnerable to long-range attacks, where an adversary corrupts past processes to re-write the history, than PoW and Proof-of-Storage systems. Proof-of-Storage-based and PoS-based protocols are both more susceptible to private double-spending attacks than PoW-based protocols; in this case, an adversary mines its chain in secret without sharing its blocks with the rest of the processes until the end of the attack. In this paper, we formally characterize the properties of resources through an abstraction called resource allocator and give a framework for understanding longest-chain consensus protocols based on different underlying resources. In addition, we use this resource allocator to demonstrate security trade-offs between various resources focusing on well-known attacks (e.g., the long-range attack and nothing-at-stake attacks).
Cite as

Sarah Azouvi, Christian Cachin, Duc V. Le, Marko Vukolić, and Luca Zanolini. Modeling Resources in Permissionless Longest-Chain Total-Order Broadcast. In 26th International Conference on Principles of Distributed Systems (OPODIS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 253, pp. 19:1-19:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{azouvi_et_al:LIPIcs.OPODIS.2022.19,
  author =	{Azouvi, Sarah and Cachin, Christian and Le, Duc V. and Vukoli\'{c}, Marko and Zanolini, Luca},
  title =	{{Modeling Resources in Permissionless Longest-Chain Total-Order Broadcast}},
  booktitle =	{26th International Conference on Principles of Distributed Systems (OPODIS 2022)},
  pages =	{19:1--19:23},
  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.2022.19},
  URN =		{urn:nbn:de:0030-drops-176398},
  doi =		{10.4230/LIPIcs.OPODIS.2022.19},
  annote =	{Keywords: blockchain, consensus, resource, broadcast}
}
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