Blockchain is a distributed ledger where each node is responsible for storing data. Depending on the difference in access control, the blockchain can be divided into a public string, a private string, and an alliance string. Public chain The public chain is fully open to the public and allows anyone, regardless of time and place, to engage in transactions and store data in a chain that only requires a device connected to the Internet. For example, BTC blockchain and ETH blockchain are both public chains. Because each node is blockchain independent, user privacy can be greatly protected. In addition, any node with the same rights can try to record and update data through a consensus mechanism. All public chain data is transparent so that everyone can check the history. The public chain is highly decentralized because it runs according to established rules, which does not allow developers or other users to make changes to rules and data. However, the trading speed is much slower because many node transactions need to be verified. Private string Unlike a public string, a private string is not open to the public, so only authorized nodes can join the string. Private chain information is released according to different needs to corresponding nodes with different rights. Because participation in a private chain requires authentication, there are not many opportunities for malicious nodes to successfully attack a high-security chain. In addition, because there are fewer nodes to authenticate, the trading speed is faster than for a public chain. However, the private chain is more centralized. It is fully managed by an organization that can change the rules, and more powerful nodes can change the data in the chain from their profits. Alliance Chain Alliance chains have allowed some organizations to participate in management together, its openness is somewhere between the private chain and the public chain. It is widely used in the financial industry to facilitate trade and settlement between institutions such as WeBank, the CBRA (China Blockchain Research Alliance) and others. and manage one or more nodes where the data is open only to members of the chain. After reaching a consensus, the constitutions were allowed to change the rules. But performance limits are more complex than for a private chain, so it has higher credit. All three of these types of blockchain have their own characteristics, so users can use one of them according to their needs. If users have no strict security requirements other than the speed of trade, a public chain is more appropriate. Conversely, if a higher rate of trade or internal data verification is required, a private string may be a better option than an alliance.