Papers Link
On the Security and Performance of Proof of Work Blockchains
Introduction
Category
- Problem Pattern: Less studied problem / Well studied problems
Motivation
Background
The security guarantees of variant (forked) PoW blockchains (which were instantiated with different parameters) have not received much attention in the literature.
Literature Review
While the security provisions of Bitcoin have been thoroughly analysed, the security guarantees of variant PoW blockchains have not received much attention in the literature. Recent studies hint that the performance of PoW based blockchains cannot be enhanced without impacting their security. However, the relationship between performance and security provisions of PoW blockchains has so far not been studied in much detail.
Research Niche
Proof of Work (PoW) consensus mechanism—which currently accounts for more than 90% of the total market capitalization of existing digital cryptocurrencies.
Work
Research Objectives
In this paper, we address this problem and provide a novel quan- titative framework to analyse the security and performance im- plications of various consensus and network parameters of PoW blockchains.
Insight
- a blockchain instance : a PoW blockchain instantiated with a given set of consensus and network parameters, such as network delays, block generation times, block sizes, information propagation mechanisms, etc
- a blockchain security model : based on Markov Decision Processes (MDP) for double-spending and selfish mining
Research Summary
- We constructed a Bitcoin blockchain simulator in order to evaluate different blockchain instances from a performance perspective.
- Selfish Mining and Double Spending security model based on MDP.
Evaluation
Evaluation Summary
- We show that selfish mining is not always a rational strategy. To capture rational adversaries, we therefore quantify the double-spending resilience of PoW blockchains and objectively compare the security of different PoW blockchains with respect to the required number of transaction confirmations.
- Due to the smaller block rewards and the higher stale block rate of Ethereum compared to Bitcoin, Ethereum is weaker.
- We show that the higher the block reward of a blockchain (in e.g., USD) the more resilient it is against double-spending.
- We analyze the impact of changing the block size and/or the block interval on selfish mining and double-spending. Blockchain can attain an effective throughput above 60 transactions per second without compromising the security of the system.
Implications
Our results show that there is considerable room to enhance the scalability of existing PoW without significantly compromising security.
Novelty
Contributions
- Double Spending MDP Model
- Blockchain Simulator
Key Concepts
强化学习（Reinforcement learning，简称RL）
机器学习中的一个领域，强调如何基于环境而行动，以取得最大化的预期利益。其灵感来源于心理学中的行为主义理论，即有机体如何在环境给予的奖励或惩罚的刺激下，逐步形成对刺激的预期，产生能获得最大利益的习惯性行为。
马尔科夫决策过程(Markov Decision Process)
马尔可夫决策过程(MDP)是一个五元组(S,A,P,R,γ)，S 是状态集合，A 是动作集合，P 是动作执行概率，R 是动作执行的回报函数，γ 是折扣函数（在本文章并没有考虑这个参数）。MDP的核心问题是为决策者找到一组策略π（动作执行序列），而这一组策略可以得到最优的累积回报。
日蚀攻击(Eclipse Attack)
在区块链网络层上的攻击，通过囤积和霸占受害者的点对点连接时隙 (slot)，将该节点保留在一个隔离的网络中。这种类型的攻击旨在阻止最新的区块链信息进入到日蚀节点，从而隔离节点
Technical Content
Quantitative Framework
Selfish-Mining MDP
Transition System
Reward Function
- Optimal relative revenue
- 如下
- Using binary search to find the vp = 0 with different p, for family of MDPs.
Double-Spending MDP
- Transition System
- Find the minimum vd that the π* contain exit state. And the lower vd, the blockchain system can be considered more resistant against double-spending attacks.
- Find the minimum vd that the π* contain exit state. And the lower vd, the blockchain system can be considered more resistant against double-spending attacks.
- Experiment Result
