Open Collections

Niu, Jianyu

University of British Columbia

Bitcoin also known as the first-generation blockchain protocol, has suffered from scalability barriers. For example, Bitcoin can only process $7$ transactions per second, and users have to wait up to one hour to confirm transactions. To address this, Ethereum, Bitcoin-NG, and HotStuff (also known as the next-generation blockchains) are proposed. Each protocol represents an elegant approach and has further influenced many subsequent blockchain protocols. Informally speaking, Ethereum promotes Bitcoin's scalability by elaborately tuning system parameters (e.g., block production rate); Bitcoin-NG achieves better scalability by decoupling Bitcoin's blockchain operation into two planes: leader election and transaction serialization; HotStuff differs from Bitcoin by renovating classic Byzantine fault tolerance (BFT) consensus protocol. However, the security and performance of these protocols have not been fully explored in the literature. Specifically, Ethereum introduces the so-called uncle and nephew rewards on top of the (standard) block rewards used in Bitcoin, making the analysis of the selfish mining attack in Bitcoin hard to be directly applied to Ethereum. This calls for new analysis. In this dissertation, a 2-dimensional Markov process is proposed to model the selfish mining attack. Besides, a probabilistic reward computing method is used to tracks block rewards. Bitcoin-NG relies on two types of blocks (namely, key blocks and microblocks) to realize the leader election and transaction serialization. However, an in-depth incentive analysis is still missing to evaluate the impact of these types of blocks under network capacity constraints. To address this, the interval between two consecutive key blocks is modeled as an exponential random variable, and the generation rate of microblocks is introduced to capture the impact of network capacity. Besides, a Markov decision process (MDP) model is used to jointly analyze the incentive of key blocks and microblock. HotStuff leverages the chain structure and pipelining techniques to simplify BFT protocol design, which, unfortunately, introduces new attacks to deteriorate the system performance. To evaluate these attacks, a multi-metric evaluation framework including chain growth rate, chain quality, and latency is proposed. Besides, two attacks, namely the forking attack and delay attack, are systematically studied. With the framework, some engineering designs in DiemBFT, a variant of HotStuff used in Facebook's Diem blockchain, are also evaluated.

Text

2021-07-20

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/79053

Electrical Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/