Blockchain based

blockchain (English: blockchain or block chain) is a kind of distributed database . You may have heard about bitcoin, which is the core technology. Blockchain is a series of data blocks generated by cryptography. Each data block contains the information of a network transaction, which is used to verify the validity of the information and generate the next block. In a popular concept, blockchain is an account that everyone can keep. In a company or organization, most people only have the right to keep accounts, while only a few people with professional training have the right to keep accounts. Of course, blockchain is not an account book in the traditional sense. It has the following three key points in technical principle: first, decentralization. In a network practicing blockchain technology, each computer covered by it can read and add records. From the perspective of account book, they are the people who keep accounts together, and there is no authoritative person to guide and correct them. Second, asymmetric encryption. Although everyone can remember this account, they will not be able to read it unless they are in the Bureau. Because, in the accounting process, everyone follows the unified encryption rules, but when reading, they must use their own unique decryption method. Therefore, although everyone keeps this constantly updated account, the part they can read is only the one they can decrypt, that is, the part related to themselves. Third, time stamp. That is, time stamp (English: timestamp), refers to the string or coded information used to identify the recorded time and date. Each block on the blockchain is arranged in sequence according to the time it is generated, and is confirmed by collective authentication. Moreover, previous records cannot be modified. Just like in an account, we can index and verify the previous content through the records after a point in time. Once these contents are confirmed, it will be more difficult to tamper with them

blockchain technology is to maintain a growing distributed database of data records. These data are associated with all the data written before through cryptography technology, which makes it difficult for the third party or even the owner of the node to tamper with. Block contains the data that need to be saved in the database, and these data are written into the database through block organization. Chain usually refers to the use of Merkle tree and other methods to check whether all the current blocks have been modified. This is familiar to code farmers who have used git for a long time. Recall how to modify git's history

blockchain technology is mainly divided into three categories, which are open, collaborative and private

public blockchain

example: bitcoin, Ethereum frontier. The data on the public blockchain can be accessed by all people, and all people can issue transactions waiting to be written into the blockchain. Participants in the consensus process (corresponding to the miners in bitcoin) maintain the security of the database through cryptography technology and built-in economic incentives. Open blockchain is completely distributed

highlights and pain points: the open blockchain is completely distributed and has all the characteristics of bitcoin. However, it needs sufficient cost to maintain the system operation and relies on built-in incentives. At present, only bitcoin in the public blockchain is safe enough. If the algorithm is the same as bitcoin, it will be safe; There are no built-in rewards, but they are not; It's easy to concentrate on the attack of computing power (for example, as long as the raid sweeps goods and a large number of graphics cards), and take jujube pills. The more valuable the data on the open blockchain is, the more important it is to examine its security, transaction cost and system scalability

federated blockchain

example: audit system tried by hyperledger and Deloitte. The nodes participating in the blockchain are selected in advance, and there is likely to be a good network connection between the nodes. Other consensus algorithms without workload proof can be used on such a blockchain. For example, a blockchain has been established among 100 financial institutions, and more than 67 institutions must agree to reach a consensus. The data on such a blockchain can be public or internal to these node participants. Distributed in a partial sense

highlights and pain points: collaborative blockchain can achieve a good connection between nodes, only need a little cost to maintain operation, provide rapid transaction processing and low transaction costs, has good scalability (but the scalability will decline with the increase of nodes), and data can have certain privacy. Developers have the ability to change the protocol under the consensus. There is no problem with bitcoin hard fork, but it also means that everyone can tamper with the data together under the consensus. Collaborative blockchain also means that the application scope of this blockchain will not be too wide, lacking the network propagation effect of bitcoin

private blockchain

example: Eris instries. The participating nodes are only users themselves, and the access and use of data have strict authority management. Most of the blockchain technologies recently announced by some financial institutions for internal use are vague, but they are probably all within this scope

highlights and pain points: private blockchain is actually a confusing term. Such a system is nothing more than a shared database in the traditional sense. Merkle tree and other methods are used to try to show that the data in it is verifiable. There are already mature solutions for such databases, and Merkle tree is only one of many mature solutions. It's easy for these projects to be "like eggs". Because the user has the final say, the data inside can not be changed, and there is not much protection for the third party. Therefore, many private blockchains exist by attaching to bitcoin, such as recording system snapshots to bitcoin regularly

Although the current blockchain technology is still in the initial stage, the advantages of this technology have begun to be reflected. In many fields, blockchain can proce great value, and I believe there will be more landing application scenarios in the future,