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Documents authored by Alpos, Orestis

Document
DOI: 10.4230/LIPIcs.AFT.2023.31
Practical Large-Scale Proof-Of-Stake Asynchronous Total-Order Broadcast

Authors: Orestis Alpos, Christian Cachin, Simon Holmgaard Kamp, and Jesper Buus Nielsen

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

Abstract
We present simple and practical protocols for generating randomness as used by asynchronous total-order broadcast. The protocols are secure in a proof-of-stake setting with dynamically changing stake. They can be plugged into existing protocols for asynchronous total-order broadcast and will turn these into asynchronous total-order broadcast with dynamic stake. Our contribution relies on two important techniques. The paper "Random Oracles in Constantinople: Practical Asynchronous Byzantine Agreement using Cryptography" [Cachin, Kursawe, and Shoup, PODC 2000] has influenced the design of practical total-order broadcast through its use of threshold cryptography. However, it needs a setup protocol to be efficient. In a proof-of-stake setting with dynamic stake this setup would have to be continually recomputed, making the protocol impractical. The work "Asynchronous Byzantine Agreement with Subquadratic Communication" [Blum, Katz, Liu-Zhang, and Loss, TCC 2020] showed how to use an initial setup for broadcast to asymptotically efficiently generate sub-sequent setups. The protocol, however, resorted to fully homomorphic encryption and was therefore not practically efficient. We adopt their approach to the proof-of-stake setting with dynamic stake, apply it to the Constantinople paper, and remove the need for fully homomorphic encryption. This results in simple and practical proof-of-stake protocols.
Cite as

Orestis Alpos, Christian Cachin, Simon Holmgaard Kamp, and Jesper Buus Nielsen. Practical Large-Scale Proof-Of-Stake Asynchronous Total-Order Broadcast. In 5th Conference on Advances in Financial Technologies (AFT 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 282, pp. 31:1-31:22, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2023)

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@InProceedings{alpos_et_al:LIPIcs.AFT.2023.31,
  author =	{Alpos, Orestis and Cachin, Christian and Kamp, Simon Holmgaard and Nielsen, Jesper Buus},
  title =	{{Practical Large-Scale Proof-Of-Stake Asynchronous Total-Order Broadcast}},
  booktitle =	{5th Conference on Advances in Financial Technologies (AFT 2023)},
  pages =	{31:1--31:22},
  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.2023.31},
  URN =		{urn:nbn:de:0030-drops-192203},
  doi =		{10.4230/LIPIcs.AFT.2023.31},
  annote =	{Keywords: Total-Order Broadcast, Atomic Broadcast, Proof of Stake, Random Beacon}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2021.44
Brief Announcement: How to Trust Strangers - Composition of Byzantine Quorum Systems

Authors: Orestis Alpos, Christian Cachin, and Luca Zanolini

Published in: LIPIcs, Volume 209, 35th International Symposium on Distributed Computing (DISC 2021)

Abstract
Trust is the basis of any distributed, fault-tolerant, or secure system. A trust assumption specifies the failures that a system, such as a blockchain network, can tolerate and determines the conditions under which it operates correctly. In systems subject to Byzantine faults, the trust assumption is usually specified through sets of processes that may fail together. Trust has traditionally been symmetric, such that all processes in the system adhere to the same, global assumption about potential faults. Recently, asymmetric trust models have also been considered, especially in the context of blockchains, where every participant is free to choose who to trust. In both cases, it is an open question how to compose trust assumptions. Consider two or more systems, run by different and possibly disjoint sets of participants, with different assumptions about faults: how can they work together? This work answers this question for the first time and offers composition rules for symmetric and for asymmetric quorum systems. These rules are static and do not require interaction or agreement on the new trust assumption among the participants. Moreover, they ensure that if the original systems allow for running a particular protocol (guaranteeing consistency and availability), then so will the joint system. At the same time, the composed system tolerates as many faults as possible, subject to the underlying consistency and availability properties. Reaching consensus with asymmetric trust in the model of personal Byzantine quorum systems (Losa et al., DISC 2019) was shown to be impossible, if the trust assumptions of the processes diverge from each other. With asymmetric quorum systems, and by applying our composition rule, we show how consensus is actually possible, even with the combination of disjoint sets of processes.
Cite as

Orestis Alpos, Christian Cachin, and Luca Zanolini. Brief Announcement: How to Trust Strangers - Composition of Byzantine Quorum Systems. In 35th International Symposium on Distributed Computing (DISC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 209, pp. 44:1-44:4, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2021)

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@InProceedings{alpos_et_al:LIPIcs.DISC.2021.44,
  author =	{Alpos, Orestis and Cachin, Christian and Zanolini, Luca},
  title =	{{Brief Announcement: How to Trust Strangers - Composition of Byzantine Quorum Systems}},
  booktitle =	{35th International Symposium on Distributed Computing (DISC 2021)},
  pages =	{44:1--44:4},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-210-5},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{209},
  editor =	{Gilbert, Seth},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2021.44},
  URN =		{urn:nbn:de:0030-drops-148468},
  doi =		{10.4230/LIPIcs.DISC.2021.44},
  annote =	{Keywords: Byzantine quorum systems, composition of quorum systems, trust models, asymmetric trust}
}
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