Research On Bitcoin Mining Attacks And Defense Schemes

Bitcoin is the first fully decentralized digital currency proposed by Nakamototo in 2008 and has received the widest attention.The security properties of Bitcoin rely on blockchain technology,which is an open ledger containing all current and historical transactions in the system.Bitcoin requires participants to use their computational power to solve a hard computational puzzle and generate a block,called PoW.The process of creating a block is called mining.Users who do these work are called miners and rewarded with new bitcoins from the system if someone generates a block by solving the puzzle.In the early stage of development,the difficulty of mining is relatively low,an individual miner can directly participate in mining by using computer CPU.As the price of Bitcoin continues to rise,more and more people participate in mining to gain profits,People are not satisfied with the current computing power,they begin to find ways to increase the computing power and produce special mining equipment:Mining machine,such as GPU(appeared in 2010)and ASIC(appeared in 2013).Some large enterprises choose to build mining pools in places where there are abundant electricity resources with lower price.Individual miner with small computing power have to wait for years to generate a block,they join in mining pools and share rewards according to the amount of work they contributed to the pool,the pooled mining has become the main mining method at present,and formed a new industrial chain;Mining.Although Bitcoin has been the most successful cryptocurrency,there are still many security problems in the system,which have attracted wide attention of researchers,attacks of Bitcoin itself such as the double spending problem,transaction malleability,privacy issues,attacks against P2P network such as eclipse attack,routing attack,attacks against Bitcoin Consensus Mechanism(PoW),and so on.The security of Bitcoin consensus mechanism is particularly important,which is guaranteed by miners' mining behavior.The most famous 51%attack on bitcoin is the attack method against the consensus mechanism.The attacker with 51%of the network's hashrate can change the existing transaction to achieve double spending and prevent the transaction confirmation,even monopolize the generation of blocks.This is the earliest mining attack.Since miners are rational,the purpose of miners or mining pools is to obtain revenue and make it maximization.By default,miners'revenue are proportional to their mining power,but miners may take some malicious mining behaviors such as withholding blocks and selectively revealing their mined blocks to obtain more revenue,resulting in three kinds of attack:block withholding attack,selfish mining and FAW attack.In block withholding attack,a miner in a pool submits only PPoWs,but not FPoWs.When an attacker attacks with part of computing power and mine privately with the rest computing power,she can earn extra rewards.In selfish mining,an attacker can unfairly earn extra rewards by deliberately generating forks,the selfish mining pool keeps its mined blocks private,secretly bifurcating the blockchain and creating a private branch,then continue mining on the private chain,selectively reveal their mined blocks to invalidate the honest miners' work and obtain more revenue.In fork after withholding(FAW)attack,attacker combine a BWH attack with intentional fork to obtain extra reward.This paper first analyzes basic principle,practical possibilities and countermeasures of 51%attack.And then we focuses on the other three kinds of attack,simulates different situations and scenarios,quantitatively analyse and discusses the impact of these attacks on miners' revenue Finally,we analyze the harm of these attacks to the Bitcoin system,summarize and discuss the current research on defense schemes against attacks,give a standard to measure defense schemes,and analyze the advantages and disadvantages of various defense schemes.