Tight Security Analysis of Nakamoto Consensus and Its Variants

Dr. Xuechao Wang is currently an Assistant Professor in Thrust of Fintech at HKUST(GZ). He obtained a PhD degree in Electrical and Computer Engineering at University of Illinois Urbana-Champaign in 2023, advised by Prof. Pramod Viswanath. Previously, he obtained a Bachelor Degree in Electronic Engineering at Tsinghua University in 2018. His research interest is in blockchains. During his PhD, he has published several papers in top conferences in the field of computer security, and his research has influenced the design of multiple public chains.

Nakamoto invented the longest chain protocol (a.k.a. Nakamoto Consensus), and claimed its security by analyzing the private double-spend attack, a race between the adversary and the honest nodes to grow a longer chain. But is it the worst attack? In this talk, I will answer the question in the affirmative for three classes of longest chain protocols, designed for different consensus models: 1) Nakamoto's original Proof-of-Work protocol; 2) Ouroboros and SnowWhite Proof-of-Stake protocols; 3) Chia Proof-of-Space protocol. As a consequence, exact characterization of the maximum tolerable adversary power is obtained for each protocol as a function of the average block time normalized by the network delay. The security analysis of these protocols is performed in a unified manner by a novel method of reducing all attacks to a race between the adversary and the honest nodes. Further, I will demonstrate that the same proof technique can be applied to conduct a tight security analysis on various DAG variants, including c-Nakamoto-PoS and Filecoin's expected consensus. Paper covered: Everything is a Race and Nakamoto Always Wins (ACM CCS 20, focused) Proof-of-Stake Longest Chain Protocols: Security vs Predictability (ConsensusDay 22, mentioned) Security Analysis of Filecoin’s Expected Consensus in the Byzantine vs Honest Model (To appear in AFT 23, mentioned)