Blockchain technology originated from Satoshi Nakamoto's basic paper Bitcoin: A Peer-to-Peer Electronic Cash System published in 2008. In the past two years, the research and application of blockchain technology has shown an explosive growth trend, which is considered to be the fifth subversive innovation of computing paradigm after mainframe, personal computer, Internet and mobile/social network, and the fourth milestone in the evolution history of human credit after blood credit, precious metal credit and central bank paper money credit. Blockchain technology is the embryonic form of the next generation of cloud computing, which is expected to completely reshape the form of human social activities like the Internet and realize the transformation from the current information Internet to the value Internet. Technical characteristics of blockchain

Blockchain has the characteristics of decentralization, time series data, collective maintenance, programmability, security and credibility. Decentralization: the verification, billing, storage, maintenance and transmission of blockchain data are all based on distributed architecture, and the trust relationship between distributed nodes is established by purely mathematical methods, not by central institutions, thus forming a decentralized and trustworthy distributed system; Time-series data: the blockchain uses a time-stamped chain block structure to store data, thus adding a time dimension to the data, with strong verifiability and traceability; Collective maintenance: the blockchain system adopts a specific economic incentive mechanism to ensure that all nodes in the distributed system can participate in the verification process of data blocks (such as the "mining" process of Bitcoin), and select specific nodes to add new blocks to the blockchain through the * * * identification algorithm; Programmable: Blockchain technology can provide a flexible script code system and support users to create advanced intelligent contracts, currencies or other decentralized applications; Security and credibility: Blockchain technology uses asymmetric cryptography to encrypt data, and at the same time relies on the powerful computing power formed by knowledge algorithms such as workload proof of each node of distributed system to resist external attacks and ensure that blockchain data cannot be tampered with or forged, so it has high security. Blockchain and Bitcoin Bitcoin are by far the most successful blockchain application scenarios. Blockchain technology solves the double payment problem and Byzantine general problem that Bitcoin system has to face in the field of digital cryptocurrency for a long time. Different from the credit endorsement mechanism of traditional central institutions (such as the central bank), bitcoin blockchain forms software-defined credit, which marks a fundamental change from centralized national credit to decentralized algorithmic credit. In recent years, with the first-Mover advantage, Bitcoin has now formed a complete ecosystem and industrial chain covering issuance, circulation and financial derivatives, which is also the main reason for its long-term market share of most digital cryptocurrencies. Development context and trend of blockchain

Blockchain technology is a general underlying technical framework, which can bring profound changes to finance, economy, science and technology and even politics. According to the current development of blockchain technology, blockchain technology will experience the blockchain 1.0 mode with programmable digital encryption currency system as the main feature, the blockchain 2.0 mode with programmable financial system as the main feature and the blockchain 3.0 mode with programmable society as the main feature. However, the above models are actually developing in parallel rather than evolving. The digital cryptocurrency system of blockchain 1.0 model is far from mature, and it is actually farther and more difficult from its vision of global currency integration. At present, the blockchain field has shown an obvious development trend driven by technological and industrial innovation, and the relevant academic research is seriously lagging behind, which needs to be followed up urgently. Basic model and key technology of blockchain

Generally speaking, the blockchain system consists of data layer, network layer, knowledge layer, incentive layer, contract layer and application layer. Among them, the data layer encapsulates the underlying data blocks and related data encryption and timestamp technologies; The network layer includes distributed networking mechanism, data distribution mechanism and data verification mechanism. * * * knowledge layer mainly encapsulates all kinds of * * * knowledge algorithms of network nodes; The incentive layer integrates economic factors into the blockchain technology system, mainly including the distribution mechanism and distribution mechanism of economic incentives; The contract layer mainly encapsulates various scripts, algorithms and intelligent contracts, which is the basis of the programmable characteristics of blockchain; The application layer encapsulates various application scenarios and cases of blockchain. In this model, the blockchain structure based on timestamp, the * * * knowledge mechanism of distributed nodes, the economic incentive based on * * * knowledge and the flexible and programmable intelligent contract are the most representative innovations of blockchain technology. Application scenarios of blockchain technology

Blockchain technology can not only be successfully applied to the field of digital cryptocurrency, but also has a wide range of application scenarios in economic, financial and social systems. According to the application status of blockchain technology, this paper summarizes the main applications of blockchain into six scenarios: digital currency, data storage, data authentication, financial transactions, asset management and election voting. Digital currency: digital currency, represented by Bitcoin, is essentially produced by a distributed network system, and its distribution process does not depend on a specific centralized institution. Data storage: The characteristics of blockchain, such as high redundancy storage, decentralization, high security and privacy protection, make it particularly suitable for storing and protecting important private data, and avoid large-scale data loss or disclosure caused by attacks on centralized institutions or improper authority management. Data authentication: Blockchain data is time stamped, verified and recorded by * * nodes, and cannot be tampered with or forged. These characteristics make blockchain widely used in various data notarization and auditing scenarios. For example, the blockchain can permanently and securely store various licenses, registration forms, permits, certificates, certificates and records issued by government agencies. Financial transactions: Blockchain technology and financial market applications have a very high degree of fit. Blockchain can spontaneously generate credit in a decentralized system and establish a financial market that does not need the credit endorsement of central institutions, thus achieving "financial disintermediation" to a large extent; At the same time, using the automatic intelligent contract and programmable characteristics of blockchain can greatly reduce costs and improve efficiency. Asset management: Blockchain can realize the confirmation, authorization and real-time monitoring of tangible assets and intangible assets. Intangible asset management has been widely used in intellectual property protection, domain name management, integral management and other fields; In terms of tangible asset management, we can combine the Internet of Things technology to form "digital intelligent assets" and realize distributed authorization and control based on blockchain. Election voting: Blockchain can realize political elections, corporate shareholder voting and other applications with low cost and high efficiency, and can be widely used in gambling, market forecasting, voting-based social manufacturing and other fields. Problems in Blockchain Technology

Security threat is the biggest problem facing blockchain so far. Among them, the blockchain based on PoW*** knowledge process mainly faces the problem of 5 1% attack, that is, nodes can successfully tamper with and forge blockchain data by mastering more than 5 1% of the computing power of the whole network. Other issues include the potential threat of emerging computing technologies to crack asymmetric encryption mechanisms and privacy protection issues. Blockchain efficiency is also an important factor restricting its application. Blockchain requires every node in the system to keep a data backup, which is extremely difficult for the growing mass data storage. Although lightweight nodes can partially solve this problem, industrial solutions suitable for larger scale still need to be developed. At present, bitcoin blockchain can only process 7 transactions per second, and the transaction confirmation time is generally 10 minute, which greatly limits the application of blockchain in most high-frequency trading scenarios in the financial system. The PoW*** identification process is highly dependent on the computing power contributed by the nodes of the blockchain network, which is mainly used to solve SHA256 hash and random number search, but it does not produce any practical social value. Therefore, it is generally considered that these computing resources are "wasted" and a lot of computing resources are wasted. How to effectively pool the network computing power of distributed nodes to solve practical problems is an important problem that blockchain technology needs to solve. As a decentralized distributed system, the blockchain network will inevitably have a game relationship of competition and cooperation between its nodes in the interaction process, such as the block interception attack game of bitcoin mine pool. The * * * knowledge process of blockchain is essentially a crowdsourcing process. How to design an incentive-compatible * * knowledge mechanism, so that the self-interested nodes in the decentralized system can verify and calculate the block data spontaneously, increase the cost of irrational behavior in the system, and curb security attacks and threats is an important scientific problem that blockchain needs to solve. Smart contracts and blockchain technology

Smart contract is a set of scenario response programming rules and logic, which is a decentralized and credible program code deployed on the blockchain. Usually, the smart contract is attached to the blockchain data (such as a bitcoin transaction) in the form of program code after being signed by all parties, and recorded in a specific block of the blockchain after P2P network propagation and node verification. Smart contracts encapsulate predefined states and transition rules, scenarios that trigger contract execution (such as arrival at a specific time or occurrence of a specific event), and response actions in a specific scenario. Blockchain can monitor the status of smart contracts in real time, and activate and execute contracts by checking external data sources and confirming that specific trigger conditions are met. Smart contracts are of great significance to blockchain technology. On the one hand, the smart contract is the activator of the blockchain, giving the static underlying blockchain data flexible and programmable mechanisms and algorithms, laying the foundation for building a programmable financial system and social system in the blockchain 2.0 and 3.0 era; On the other hand, the automation and programmability of smart contract enable it to encapsulate the complex behavior of each node in the distributed blockchain system and become a software agent robot in the virtual world composed of blockchain, which is helpful to promote the application of blockchain technology in various distributed artificial intelligence systems and make it possible to build various decentralized applications based on blockchain technology. Dapp), decentralized autonomous organization (DAO), decentralized autonomous company (DAC) and even decentralized autonomous society (DAS) become possible. The main development trend of blockchain and smart contract technology is the evolution from automation to intelligence. Most of the existing smart contracts and their applications are still based on the "if-then" type conditional response rules of predefined scenarios, which can meet the needs of current automated transactions and data processing. The future smart contract should have the functions of "hypothesis" deduction, calculation experiment and a certain degree of independent decision-making according to unknown scenarios, so as to realize the leap from the current "automation" contract to the real "smart" contract. Blockchain-driven parallel society

In recent years, a parallel society based on CPSS (Network-Physical-Social System) has emerged, and its core and essential feature is the interaction and parallel evolution between reality and reality. Blockchain is one of the infrastructures to realize CPSS parallel society. Its main contribution is to provide an effective decentralized data structure, interaction mechanism and calculation mode for the research of distributed social systems and distributed artificial intelligence, and to lay a solid data foundation and credit foundation for the realization of parallel society. As far as data base is concerned, management scientist Edward Deming once said: Everyone must speak with data except God. In a centralized social system, data is usually in the hands of "a few people" such as the government and large enterprises, and its fairness, authority and even security may not be guaranteed. Blockchain data is stored by highly redundant distributed nodes and is in the hands of "everyone", which can realize real "data democracy". As far as the credit basis is concerned, the centralized social system must have the characteristics of "Merton system" because of its high engineering complexity and social complexity, that is, uncertainty, diversity and complexity, and the central institutions and rulemakers in the social system may break their promises because of individual interests; Blockchain technology helps to realize a software-defined social system. Its basic idea is to eliminate centralized institutions, deploy and solidify unpredictable behaviors in blockchain data in advance in the form of programmed codes of intelligent contracts, which cannot be forged and tampered with afterwards and automatically executed, thus, to a certain extent, the "Merton" social system can be transformed into a "Newton" social system that can be comprehensively observed, actively controlled and accurately predicted. ACP (Artificial Society, Computational Experiment and Parallel Execution) method is the only systematic and complete research framework in the field of parallel social management so far, and it is the logical extension and innovation of complexity science in the new era of parallel social environment. ACP method can be naturally combined with blockchain technology to realize blockchain-driven parallel social management. First of all, P2P network of blockchain, distributed knowledge cooperation and contribution-based economic incentives are the natural modeling of distributed social system, in which each node will be an autonomous and autonomous agent in the distributed system. With the improvement of the blockchain ecosystem, all the nodes in the blockchain and the increasingly complex and autonomous smart contracts will form DAC and DAO in specific organizational forms by participating in various forms of Dapp, and finally form DAS, that is, the artificial society in ACP. Secondly, the programmable nature of smart contracts enables the blockchain to carry out various types of "hypothetical" virtual experiment design, scenario deduction and result evaluation, and through this computational experiment process, the optimal decision can be obtained and executed automatically or semi-automatically. Finally, the intelligent assets formed by the combination of blockchain and the Internet of Things make it possible to connect the real physical world with the virtual cyberspace, and realize the collaborative optimization of social management and decision-making through the interaction and parallel tuning between the real and artificial social systems. It is not difficult to foresee that when the physical assets in the real physical world are registered as smart assets in the chain in the future, it is the time when the blockchain-driven parallel society comes.