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Documents authored by Monti, Matteo

Document
DOI: 10.4230/LIPIcs.DISC.2023.13
Every Bit Counts in Consensus

Authors: Pierre Civit, Seth Gilbert, Rachid Guerraoui, Jovan Komatovic, Matteo Monti, and Manuel Vidigueira

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

Abstract
Consensus enables n processes to agree on a common valid L-bit value, despite t < n/3 processes being faulty and acting arbitrarily. A long line of work has been dedicated to improving the worst-case communication complexity of consensus in partial synchrony. This has recently culminated in the worst-case word complexity of O(n²). However, the worst-case bit complexity of the best solution is still O(n²L + n²κ) (where κ is the security parameter), far from the Ω(nL + n²) lower bound. The gap is significant given the practical use of consensus primitives, where values typically consist of batches of large size (L > n). This paper shows how to narrow the aforementioned gap. Namely, we present a new algorithm, DARE (Disperse, Agree, REtrieve), that improves upon the O(n²L) term via a novel dispersal primitive. DARE achieves O(n^{1.5}L + n^{2.5}κ) bit complexity, an effective √n-factor improvement over the state-of-the-art (when L > nκ). Moreover, we show that employing heavier cryptographic primitives, namely STARK proofs, allows us to devise DARE-Stark, a version of DARE which achieves the near-optimal bit complexity of O(nL + n²poly(κ)). Both DARE and DARE-Stark achieve optimal O(n) worst-case latency.
Cite as

Pierre Civit, Seth Gilbert, Rachid Guerraoui, Jovan Komatovic, Matteo Monti, and Manuel Vidigueira. Every Bit Counts in Consensus. In 37th International Symposium on Distributed Computing (DISC 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 281, pp. 13:1-13:26, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{civit_et_al:LIPIcs.DISC.2023.13,
  author =	{Civit, Pierre and Gilbert, Seth and Guerraoui, Rachid and Komatovic, Jovan and Monti, Matteo and Vidigueira, Manuel},
  title =	{{Every Bit Counts in Consensus}},
  booktitle =	{37th International Symposium on Distributed Computing (DISC 2023)},
  pages =	{13:1--13:26},
  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.2023.13},
  URN =		{urn:nbn:de:0030-drops-191399},
  doi =		{10.4230/LIPIcs.DISC.2023.13},
  annote =	{Keywords: Byzantine consensus, Bit complexity, Latency}
}
Document
DOI: 10.4230/LIPIcs.DISC.2022.13
Oracular Byzantine Reliable Broadcast

Authors: Martina Camaioni, Rachid Guerraoui, Matteo Monti, and Manuel Vidigueira

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

Abstract
Byzantine Reliable Broadcast (BRB) is a fundamental distributed computing primitive, with applications ranging from notifications to asynchronous payment systems. Motivated by practical consideration, we study Client-Server Byzantine Reliable Broadcast (CSB), a multi-shot variant of BRB whose interface is split between broadcasting clients and delivering servers. We present Draft, an optimally resilient implementation of CSB. Like most implementations of BRB, Draft guarantees both liveness and safety in an asynchronous environment. Under good conditions, however, Draft achieves unparalleled efficiency. In a moment of synchrony, free from Byzantine misbehaviour, and at the limit of infinitely many broadcasting clients, a Draft server delivers a b-bits payload at an asymptotic amortized cost of 0 signature verifications, and (log₂(c) + b) bits exchanged, where c is the number of clients in the system. This is the information-theoretical minimum number of bits required to convey the payload (b bits, assuming it is compressed), along with an identifier for its sender (log₂(c) bits, necessary to enumerate any set of c elements, and optimal if broadcasting frequencies are uniform or unknown). These two achievements have profound practical implications. Real-world BRB implementations are often bottlenecked either by expensive signature verifications, or by communication overhead. For Draft, instead, the network is the limit: a server can deliver payloads as quickly as it would receive them from an infallible oracle.
Cite as

Martina Camaioni, Rachid Guerraoui, Matteo Monti, and Manuel Vidigueira. Oracular Byzantine Reliable Broadcast. In 36th International Symposium on Distributed Computing (DISC 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 246, pp. 13:1-13:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{camaioni_et_al:LIPIcs.DISC.2022.13,
  author =	{Camaioni, Martina and Guerraoui, Rachid and Monti, Matteo and Vidigueira, Manuel},
  title =	{{Oracular Byzantine Reliable Broadcast}},
  booktitle =	{36th International Symposium on Distributed Computing (DISC 2022)},
  pages =	{13:1--13:19},
  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.2022.13},
  URN =		{urn:nbn:de:0030-drops-172048},
  doi =		{10.4230/LIPIcs.DISC.2022.13},
  annote =	{Keywords: Byzantine reliable broadcast, Good-case complexity, Amortized complexity, Batching}
}
Document
DOI: 10.4230/LIPIcs.DISC.2019.22
Scalable Byzantine Reliable Broadcast

Authors: Rachid Guerraoui, Petr Kuznetsov, Matteo Monti, Matej Pavlovic, and Dragos-Adrian Seredinschi

Published in: LIPIcs, Volume 146, 33rd International Symposium on Distributed Computing (DISC 2019)

Abstract
Byzantine reliable broadcast is a powerful primitive that allows a set of processes to agree on a message from a designated sender, even if some processes (including the sender) are Byzantine. Existing broadcast protocols for this setting scale poorly, as they typically build on quorum systems with strong intersection guarantees, which results in linear per-process communication and computation complexity. We generalize the Byzantine reliable broadcast abstraction to the probabilistic setting, allowing each of its properties to be violated with a fixed, arbitrarily small probability. We leverage these relaxed guarantees in a protocol where we replace quorums with stochastic samples. Compared to quorums, samples are significantly smaller in size, leading to a more scalable design. We obtain the first Byzantine reliable broadcast protocol with logarithmic per-process communication and computation complexity. We conduct a complete and thorough analysis of our protocol, deriving bounds on the probability of each of its properties being compromised. During our analysis, we introduce a novel general technique that we call adversary decorators. Adversary decorators allow us to make claims about the optimal strategy of the Byzantine adversary without imposing any additional assumptions. We also introduce Threshold Contagion, a model of message propagation through a system with Byzantine processes. To the best of our knowledge, this is the first formal analysis of a probabilistic broadcast protocol in the Byzantine fault model. We show numerically that practically negligible failure probabilities can be achieved with realistic security parameters.
Cite as

Rachid Guerraoui, Petr Kuznetsov, Matteo Monti, Matej Pavlovic, and Dragos-Adrian Seredinschi. Scalable Byzantine Reliable Broadcast. In 33rd International Symposium on Distributed Computing (DISC 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 146, pp. 22:1-22:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{guerraoui_et_al:LIPIcs.DISC.2019.22,
  author =	{Guerraoui, Rachid and Kuznetsov, Petr and Monti, Matteo and Pavlovic, Matej and Seredinschi, Dragos-Adrian},
  title =	{{Scalable Byzantine Reliable Broadcast}},
  booktitle =	{33rd International Symposium on Distributed Computing (DISC 2019)},
  pages =	{22:1--22:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-126-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{146},
  editor =	{Suomela, Jukka},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2019.22},
  URN =		{urn:nbn:de:0030-drops-113293},
  doi =		{10.4230/LIPIcs.DISC.2019.22},
  annote =	{Keywords: Byzantine reliable broadcast, probabilistic distributed algorithms, scalable distributed systems, stochastic processes}
}
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