Analysis And Optimization Of Blockchain Pow Consensus Algorithm Based On ZD Strategies

Blockchain is a new type of decentralized distributed system that is popular with digital cryptocurrencies such as bitcoin.It has the characteristics of decentralization,time series data,collective maintenance,programmability and safety and credibility.At present,blockchain has drawn great attention and widespread concern from government departments,financial institutions,technology companies and capital markets.How to reach a consensus efficiently in a decentralized distributed system is an important issue in the research of blockchain technology.Bitcoin employs blockchain as the underlying framework support technology,and reaches consensus among miners through Proof of Work(PoW)consensus mechanism,and system security is ensured by the strong power generated in the consensus process.Miners join in the pool in return for a steady payoff,with cooperative mining,and earn the corresponding payoffs through contribution power.Miners reached a "friendly" consensus,not only to ensure system security,but to ensure environmentally friendly mining--power is not wasted.However,miners can also attack and as "free rider" to share the system revenue with other miners.Such attack forms an "unfriendly" consensus,and attackers will gain more than their contribution,whereas others will earn less than attackers should not attack.Each miner's payoff is zero when all the miners attack each other,system revenue will be zero as well,which is a dilemma among miners,corresponding to the prisoners'dilemma in game theory,i.e.,attack is the best choice for a single miner,but not system optimal.This paper solves mining problem by using Zero Determinant(ZD)strategy and optimizes the strategy choices of nodes so as to obtain the higher revenue of system.Firstly,during PoW consensus process,considering whether miners have same power or not,the existence condition of Nash Equilibrium of miners strategy selection is analyzed.Single miner's ZD strategy is applied to the mining model,the game is optimized and the related conclusions are given.Then considering two types of special ZD strategies:pinning strategy can control opponent's payoff;extortion strategy can force opponent's payoff and its payoff to satisfy a linear relationship.Under certain conditions,both pinning strategy and extortion strategy can relatively increase system revenue,but miners still have the possibility of attack,and system revenue has not reached the highest value.Based on the strengths and weaknesses of the single ZD strategy,multi-ZD strategies is finally considered.We analyze and compare the changes in system revenue when there are multiple miners in a pool,and from zero miner mining with ZD strategy to multiple.Depending on Markov Chain,it proves that multi-miner multi-ZD strategies can ensure that miners reach a friendly consensus,and then cooperate mining to get rid of mining dilemma,and to obtain the highest system revenue.Numerical simulation is used to verify the effectiveness and feasibility of ZD strategy.The design of effective consensus mechanisms has been a central issue in blockchain.In the blockchain PoW consensus algorithm,Nash Equilibrium is mutual attack.That is,the optimal choices of miners' in mining dilemma are to attack each other.This kind of attack causes a waste of the power of the blockchain system and also causes the"destructive consensus",system completely lost its trust and will eventually cannot to continue operation.Therefore,designing a friendly approach to realize consensus is an important issue for the continued development of blockchain technology.This paper comprehends and analyzes PoW consensus algorithm by game theory,and proposes to optimize the mining strategy selection of PoW consensus algorithm by applying ZD strategy.After two improvements,multi-miner multi-ZD strategies is finally considered.This strategy enables miners to mine cooperatively,and it achieves optimal system revenue.This paper delimits mining dilemma according to game theory by analyzing the process of mining,which provides theory for the research prospects and applications of blockchain,and it also provides new ideas and methods for the optimization and design the blockchain consensus algorithms.