Efficient and resilient consensus for permissioned blockchain

Xiang, Zhuolun

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https://hdl.handle.net/2142/115413 Copy

Description

Title

Efficient and resilient consensus for permissioned blockchain

Author(s)

Xiang, Zhuolun

Issue Date

2022-04-21

Director of Research (if dissertation) or Advisor (if thesis)

Ren, Ling

Doctoral Committee Chair(s)

Ren, Ling

Committee Member(s)

• Gupta, Indranil
• Vaidya, Nitin H.
• Viswanath, Pramod
• Shi, Elaine

Department of Study

Computer Science

Discipline

Computer Science

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• consensus
• Byzantine fault
• blockchain

Abstract

Reaching consensus among different participants in a distributed system is a fundamental problem that has been studied extensively in the past decades. Due to the recent popularity of digital currency and the need to build high-performance decentralized financial infrastructures, the classic consensus problem attracts renewed attention. This thesis investigates consensus in the permissioned setting where the participants know each other's identities. In contrast to permissionless consensus protocols like Nakamoto consensus that relies on expensive proof-of-work or other mechanisms against Sybil attacks, permissioned consensus can offer better performance without high energy consumption, thus suitable for applications like permissioned blockchain. While decades of research on permissioned consensus already developed numerous protocols and impossibility results, many challenges and open problems still arise to build an efficient and robust permissioned blockchain. In this thesis, I will first present several theoretical results on the communication complexity and latency that fundamentally improve the state-of-the-art, and then present several practical consensus protocols that can enhance the robustness of existing permissioned blockchain systems. More specifically, I will first propose extension protocols for Byzantine agreement and broadcast with improved communication complexity, where the extension protocol can solve the problem with long inputs using single-bit instances. Then, I will show results for the good-case latency of Byzantine broadcast, which measures the commit latency under a non-faulty broadcaster. A complete categorization of the tight bounds of the good-case latency will be presented for both authenticated and unauthenticated settings with various network models. Next, I will describe the notion of strengthened fault tolerance which can enhance the fault tolerance of chain-based BFT from one-third up to two-thirds during the optimistic period. Finally, I will propose an asynchronous fallback protocol that can replace the view-change of partially synchronous BFT protocols like HotStuff, to obtain a network-adaptive consensus protocol with optimal communication cost on and off the happy path, and makes progress even under asynchrony.

Graduation Semester

2022-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Zhuolun Xiang

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