# A Survey of Distributed Consensus Protocols for Blockchain Networks

## TL;DR

This survey comprehensively reviews and analyzes various blockchain consensus protocols, highlighting their components, performance metrics, and suitability for different applications to guide future protocol development.

## Contribution

It introduces a five-component framework for analyzing consensus protocols and provides a detailed comparison of existing protocols using this framework.

## Key findings

- Identifies key components of blockchain consensus protocols.
- Provides a comparative analysis of protocols based on performance metrics.
- Offers insights into the trade-offs and application scenarios of different protocols.

## Abstract

Since the inception of Bitcoin, cryptocurrencies and the underlying blockchain technology have attracted an increasing interest from both academia and industry. Among various core components, consensus protocol is the defining technology behind the security and performance of blockchain. From incremental modifications of Nakamoto consensus protocol to innovative alternative consensus mechanisms, many consensus protocols have been proposed to improve the performance of the blockchain network itself or to accommodate other specific application needs. In this survey, we present a comprehensive review and analysis on the state-of-the-art blockchain consensus protocols. To facilitate the discussion of our analysis, we first introduce the key definitions and relevant results in the classic theory of fault tolerance which help to lay the foundation for further discussion. We identify five core components of a blockchain consensus protocol, namely, block proposal, block validation, information propagation, block finalization, and incentive mechanism. A wide spectrum of blockchain consensus protocols are then carefully reviewed accompanied by algorithmic abstractions and vulnerability analyses. The surveyed consensus protocols are analyzed using the five-component framework and compared with respect to different performance metrics. These analyses and comparisons provide us new insights in the fundamental differences of various proposals in terms of their suitable application scenarios, key assumptions, expected fault tolerance, scalability, drawbacks and trade-offs. We believe this survey will provide blockchain developers and researchers a comprehensive view on the state-of-the-art consensus protocols and facilitate the process of designing future protocols.