International Joint Conference On Theoretical Computer Science – Frontier of Algorithmic Wisdom

August 15-19, 2022, City University of Hong Kong, Hong Kong


Invited Speakers

Track B

A Rational Protocol Treatment of 51% Attacks

Vassilis Zikas

Purdue University

Game-theoretic analyses of cryptocurrencies and---more generally---blockchain-based decentralized ledgers offer insight on their economic robustness and behavior when even their underpinning cryptographic assumptions fail. In this work we utilize the recently proposed blockchain adaptation of the rational protocol design (RPD) framework [EUROCRYPT'18] to analyze 51% double-spending attacks against Nakamoto-style proof-of-work based cryptocurrencies. We first observe a property of the originally proposed utility class that yields an unnatural conclusion against such attacks, and show how to devise a utility that avoids this pitfall and makes predictions that match the observable behavior---i.e., that renders attacking a dominant strategy in settings where an attack was indeed observed in reality. We then propose a generic remedy to the underlying protocol parameters that provably deter adversaries controlling a majority of the system's resources from attacks on blockchain consistency, including the 51% double-spending attack. This can be used as guidance to patch systems that have suffered such attacks, e.g., Ethereum Classic and Bitcoin Cash, and serves as a demonstration of the power of game-theoretic analyses.
This is joint work with Christian Badertscher and Yun Lu.

Vassilis Zikas is an Associate Professor at the Computer Science Department at Purdue University, and director of the Purdue Blockchain Lab. Prior to his current position, he was an Associate Professor (Sr. Lecturer) in Security and Privacy and the Vice Director of the Blockchain Technology Lab at the University of Edinburgh; a Research Fellow and Area Leader of multi-party computation for IOHK---a leading research-and-development company in the area of blockchain technologies and distributed ledger; an Assistant Professor at Rensselaer Polytechnic Institute (RPI), Troy, NY; a Fellow of the Simons Institute for the Theory of Computing at UC Berkeley; a Senior Researcher at ETH Zurich, and a postdoctoral researcher at UCLA and at the University of Maryland.