5 Search Results for "Danezis, George"


Document
Invited Talk
Efficient DAG-Based Consensus (Invited Talk)

Authors: Alberto Sonnino

Published in: OASIcs, Volume 101, 5th International Symposium on Foundations and Applications of Blockchain 2022 (FAB 2022)


Abstract
This talk shows how to build high-performant Byzantine fault-tolerant (BFT) quorum-based consensus cores. The talks starts by challenging the common misconception that the overall communication complexity of the protocol is the key factor determining performance. We instead argue that the bottleneck of many state-of-the-art consensus protocols is their sequential use of the machine’s resources (network, storage, CPU), and that data dissemination is the most resource-intensive task. In light of the above considerations, the first insight to build performant BFT-based consensus cores is to separate the task of reliable transaction dissemination from transaction ordering. We show how to design a new DAG-based mempool protocol, called Narwhal, specialising in high-throughput reliable dissemination and storage of causal histories of transactions. Narwhal tolerates an asynchronous network and maintains high performance despite failures. It is designed to easily scale-out using multiple workers at each validator to concurrently use the machine’s resources (network, storage, CPU), and demonstrates that there is no foreseeable limit to the throughput we can achieve. We then present two ways to leverage Narwhal to achieve consensus. We first (i) present Tusk, a zero-message overhead asynchronous consensus protocol designed to work with Narwhal. Tusk achieves an unprecedented 160,000 tx/s with about 3 seconds latency in a geo-replicated environment. We then (ii) show how any partially-synchronous consensus, such as HotStuff (PODC 19), can be composed with Narwhal to drastically improve its performance. HotStuff running over Narwhal sees its throughput increase from about 2,000 tx/s to over 130,000 tx/s without noticeable latency increase. The talk concludes by illustrating how to properly evaluate performance of BFT-based consensus cores. It highlights the most common mistakes seen in the literature, such as benchmarks with empty transactions (empty load), performance approximation based on LAN-only benchmarks, and using a single burst of input transactions. We then show how to analyse benchmark results using latency-throughput graphs (L-graphs) and SLA-based throughput graphs. Author Bio. I am a system researcher at Mysten Labs, based in London (UK). I previously was a research scientist at Facebook (now called Meta) in the blockchain and cryptography team. Before joining Facebook, I co-founded chainspace.io which built a scalable smart contract platform; the team was then acquired by Facebook. My research interests are in systems security and privacy engineering. My main areas of research include distributed systems, blockchains, and privacy enhancing technologies. I have a special interest in cryptography, and I spend most of my time designing, implementing and evaluating high-performance distributed systems.

Cite as

Alberto Sonnino. Efficient DAG-Based Consensus (Invited Talk). In 5th International Symposium on Foundations and Applications of Blockchain 2022 (FAB 2022). Open Access Series in Informatics (OASIcs), Volume 101, p. 4:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)


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@InProceedings{sonnino:OASIcs.FAB.2022.4,
  author =	{Sonnino, Alberto},
  title =	{{Efficient DAG-Based Consensus}},
  booktitle =	{5th International Symposium on Foundations and Applications of Blockchain 2022 (FAB 2022)},
  pages =	{4:1--4:1},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-248-8},
  ISSN =	{2190-6807},
  year =	{2022},
  volume =	{101},
  editor =	{Tucci-Piergiovanni, Sara and Crooks, Natacha},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/OASIcs.FAB.2022.4},
  URN =		{urn:nbn:de:0030-drops-162712},
  doi =		{10.4230/OASIcs.FAB.2022.4},
  annote =	{Keywords: Consensus protocol, Byzantine Fault Tolerant}
}
Document
Twins: BFT Systems Made Robust

Authors: Shehar Bano, Alberto Sonnino, Andrey Chursin, Dmitri Perelman, Zekun Li, Avery Ching, and Dahlia Malkhi

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


Abstract
This paper presents Twins, an automated unit test generator of Byzantine attacks. Twins implements three types of Byzantine behaviors: (i) leader equivocation, (ii) double voting, and (iii) losing internal state such as forgetting "locks" guarding voted values. To emulate interesting attacks by a Byzantine node, it instantiates twin copies of the node instead of one, giving both twins the same identities and network credentials. To the rest of the system, the twins appear indistinguishable from a single node behaving in a "questionable" manner. Twins can systematically generate Byzantine attack scenarios at scale, execute them in a controlled manner, and examine their behavior. Twins scenarios iterate over protocol rounds and vary the communication patterns among nodes. Twins runs in a production setting within DiemBFT where it can execute 44M Twins-generated scenarios daily. Whereas the system at hand did not manifest errors, subtle safety bugs that were deliberately injected for the purpose of validating the implementation of Twins itself were exposed within minutes. Twins can prevent developers from regressing correctness when updating the codebase, introducing new features, or performing routine maintenance tasks. Twins only requires a thin wrapper over DiemBFT, we thus envision other systems using it. Building on this idea, one new attack and several known attacks against other BFT protocols were materialized as Twins scenarios. In all cases, the target protocols break within fewer than a dozen protocol rounds, hence it is realistic for the Twins approach to expose the problems.

Cite as

Shehar Bano, Alberto Sonnino, Andrey Chursin, Dmitri Perelman, Zekun Li, Avery Ching, and Dahlia Malkhi. Twins: BFT Systems Made Robust. In 25th International Conference on Principles of Distributed Systems (OPODIS 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 217, pp. 7:1-7:29, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)


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@InProceedings{bano_et_al:LIPIcs.OPODIS.2021.7,
  author =	{Bano, Shehar and Sonnino, Alberto and Chursin, Andrey and Perelman, Dmitri and Li, Zekun and Ching, Avery and Malkhi, Dahlia},
  title =	{{Twins: BFT Systems Made Robust}},
  booktitle =	{25th International Conference on Principles of Distributed Systems (OPODIS 2021)},
  pages =	{7:1--7:29},
  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-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2021.7},
  URN =		{urn:nbn:de:0030-drops-157825},
  doi =		{10.4230/LIPIcs.OPODIS.2021.7},
  annote =	{Keywords: Distributed Systems, Byzantine Fault Tolerance, Real-World Deployment}
}
Document
Brief Announcement
Brief Announcement: Twins – BFT Systems Made Robust

Authors: Shehar Bano, Alberto Sonnino, Andrey Chursin, Dmitri Perelman, Zekun Li, Avery Ching, and Dahlia Malkhi

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


Abstract
Twins is an effective strategy for generating test scenarios with Byzantine [Lamport et al., 1982] nodes in order to find flaws in Byzantine Fault Tolerant (BFT) systems. Twins finds flaws in the design or implementation of BFT protocols that may cause correctness issues. The main idea of Twins is the following: running twin instances of a node that use correct, unmodified code and share the same network identity and credentials allows to emulate most interesting Byzantine behaviors. Because a twin executes normal, unmodified node code, building Twins only requires a thin wrapper over an existing distributed system designed for Byzantine tolerance. To emulate material, interesting scenarios with Byzantine nodes, it instantiates one or more twin copies of the node, giving the twins the same identities and network credentials as the original node. To the rest of the system, the node and all its twins appear indistinguishable from a single node behaving in a "questionable" manner. This approach generates many interesting Byzantine behaviors, including equivocation, double voting, and losing internal state, while forgoing uninteresting behavior scenarios that can be filtered at the transport layer, such as producing semantically invalid messages. Building on configurations with twin nodes, Twins systematically generates scenarios with Byzantine nodes via enumeration over protocol rounds and communication patterns among nodes. Despite this being inherently exponential, one new flaw and several known flaws were materialized by Twins in the arena of BFT consensus protocols. In all cases, protocols break within fewer than a dozen protocol rounds, hence it is realistic for the Twins approach to expose the problems. In two of these cases, it took the community more than a decade to discover protocol flaws that Twins would have surfaced within minutes. Additionally, Twins has been incorporated into the continuous release testing process of a production setting (DiemBFT) in which it can execute 44M Twins-generated scenarios daily.

Cite as

Shehar Bano, Alberto Sonnino, Andrey Chursin, Dmitri Perelman, Zekun Li, Avery Ching, and Dahlia Malkhi. Brief Announcement: Twins – BFT Systems Made Robust. In 35th International Symposium on Distributed Computing (DISC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 209, pp. 46:1-46:4, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)


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@InProceedings{bano_et_al:LIPIcs.DISC.2021.46,
  author =	{Bano, Shehar and Sonnino, Alberto and Chursin, Andrey and Perelman, Dmitri and Li, Zekun and Ching, Avery and Malkhi, Dahlia},
  title =	{{Brief Announcement: Twins – BFT Systems Made Robust}},
  booktitle =	{35th International Symposium on Distributed Computing (DISC 2021)},
  pages =	{46:1--46:4},
  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-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2021.46},
  URN =		{urn:nbn:de:0030-drops-148485},
  doi =		{10.4230/LIPIcs.DISC.2021.46},
  annote =	{Keywords: Distributed Systems, Byzantine Fault Tolerance, Real-World Deployment}
}
Document
Privacy and Security in Smart Energy Grids (Dagstuhl Seminar 16032)

Authors: George Danezis, Stefan Katzenbeisser, Christiane Peters, and Bart Preneel

Published in: Dagstuhl Reports, Volume 6, Issue 1 (2016)


Abstract
This report documents the program and the outcomes of Dagstuhl Seminar 16032 "Privacy and Security in Smart Energy Grids". Smart electricity grids augment the electricity distribution network with modern communications and computerized control to improve efficiency, reliability, and security of electricity distribution, and more flexible production. This initiative has been greeted by consumers and utilities not only with enthusiasm but also concern. Consumers worry about their privacy. Utilities worry about the security of their assets. These outcries and reactions have triggered academics and industry to look into designing privacy friendly architectures for smart metering. The Dagstuhl Seminar 16032 brought together academic researchers as well as utility experts in order to start an open dialogue on smart grid privacy and security problems and potential solutions to support customers and utilities. A particular focus of the seminar were problems related to two timely use-cases for the smart grid, namely smart charging of electric vehicles and distribution automation.

Cite as

George Danezis, Stefan Katzenbeisser, Christiane Peters, and Bart Preneel. Privacy and Security in Smart Energy Grids (Dagstuhl Seminar 16032). In Dagstuhl Reports, Volume 6, Issue 1, pp. 99-107, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)


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@Article{danezis_et_al:DagRep.6.1.99,
  author =	{Danezis, George and Katzenbeisser, Stefan and Peters, Christiane and Preneel, Bart},
  title =	{{Privacy and Security in Smart Energy Grids (Dagstuhl Seminar 16032)}},
  pages =	{99--107},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2016},
  volume =	{6},
  number =	{1},
  editor =	{Danezis, George and Katzenbeisser, Stefan and Peters, Christiane and Preneel, Bart},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagRep.6.1.99},
  URN =		{urn:nbn:de:0030-drops-58160},
  doi =		{10.4230/DagRep.6.1.99},
  annote =	{Keywords: Critical infrastructure protection, smart energy grids}
}
Document
Improving the Decoding Efficiency of Private Search

Authors: George Danezis and Claudia Diaz

Published in: Dagstuhl Seminar Proceedings, Volume 5411, Anonymous Communication and its Applications (2006)


Abstract
We show two ways of recovering all matching documents, in the Ostrovsky et al. Private Search, while requiring considerably shorter buffers. Both schemes rely on the fact that documents colliding in a buffer position provide the sum of their plaintexts. Efficient decoding algorithms can make use of this property to recover documents never present alone in a buffer position.

Cite as

George Danezis and Claudia Diaz. Improving the Decoding Efficiency of Private Search. In Anonymous Communication and its Applications. Dagstuhl Seminar Proceedings, Volume 5411, pp. 1-11, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2006)


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@InProceedings{danezis_et_al:DagSemProc.05411.3,
  author =	{Danezis, George and Diaz, Claudia},
  title =	{{Improving the Decoding Efficiency of Private Search}},
  booktitle =	{Anonymous Communication and its Applications},
  pages =	{1--11},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2006},
  volume =	{5411},
  editor =	{Shlomi Dolev and Rafail Ostrovsky and Andreas Pfitzmann},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagSemProc.05411.3},
  URN =		{urn:nbn:de:0030-drops-4829},
  doi =		{10.4230/DagSemProc.05411.3},
  annote =	{Keywords: Private search, private information retrieval, cryptography}
}
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