Friday, May 9
SEC LL2.221 or Zoom (Passcode: 988031)
11:00am - 12:00pm

How Does Bitcoin Achieve Consensus? How Can Longest-Chain Protocols Be Attacked?
Dongning Guo, Professor, Northwestern University

Abstract: Since Bitcoin's inception in 2008, blockchain technology has transformed digital trust, enabling secure consensus and peer-to-peer transactions without a central authority. This seminar delves into the core mechanics of longest-chain consensus protocols and their security vulnerabilities. These protocols instruct each miner or validator to extend the chain they perceive as the longest. When a sufficient majority of the network follows this rule, the protocol ensures that a block becomes increasingly secure as it accumulates more confirmations within the longest chain. We construct a Markov decision process (MDP) model from scratch to precisely represent the system’s state, the adversary’s potential actions, and state transitions driven by the adversarial action and random block arrivals. We investigate how an adversary can optimally compromise block safety and quantify the resulting probability of security violations. Our findings offer fresh insights into the interplay of network delay, transaction throughput, and blockchain security.

Biography: Dongning Guo earned his Ph.D. in Electrical Engineering from Princeton University in 2004. He then joined Northwestern University in Evanston, IL, where he is now a Professor in the Department of Electrical and Computer Engineering and, by courtesy, a Professor of Computer Science. From 1998 to 1999, he worked as an R&D Engineer at the Center for Wireless Communications in Singapore. He has held editorial roles, including Associate Editor for IEEE Transactions on Information Theory and IEEE Transactions on Wireless Communications, Editor of Foundations and Trends in Communications and Information Theory, and Guest Editor for the IEEE Journal on Selected Areas in Communications. His accolades include the NSF CAREER Award (2007), the IEEE Marconi Prize Paper Award in Wireless Communications (2010), the Best Paper Award at the IEEE Wireless Communications and Networking Conference (2017), and the Bitcoin Research Prize (2023). He also led teams to the finals of the DARPA Spectrum Challenges in 2014 and 2019. Elected an IEEE Fellow in 2020, his research focuses on blockchain and decentralization, information theory, and wireless networks.