Blockchain is a database structure composed of "blocks" one after another. Each block Data of a certain size is stored in it, and the blocks are connected according to the time sequence of their respective generation to form a chain structure, which forms a blockchain.

What is a block? What are blocks made of? Please refer to the "What is a Block" section.

Compared with traditional databases, blockchain generally has the following core characteristics: Decentralization, Difficult to tamper, Open and transparent

What is decentralization? Why does blockchain have the characteristics of decentralization?

Decentralization refers to how power is given to people around the world to manage, rather than being managed centrally by one person or entity.

The blockchain system is jointly maintained by many servers. Each server participating in maintenance stores a copy of all data in the blockchain. As long as there is still one server in the entire system that is still operating, the blockchain The data on it will not be lost. These servers are called "nodes" in the blockchain system, and they provide storage space and computing support for the entire system.

If you want to record a new piece of data in the blockchain system, all nodes must agree on the data - if more than half of the nodes agree, all nodes will record it together. The nodes of the blockchain are usually run by different entities and have no connection outside the blockchain system. Therefore, we can believe that the blockchain is not run by a single individual or entity, but is jointly maintained by multiple parties. This is also the core feature of the blockchain that people often say: decentralization.

What is a node? How do these nodes work together through a "consensus mechanism"? What is a consensus mechanism? Please refer to the "What is a Node/Validator" and "What is the Consensus Mechanism" chapters.

Why is the data in the blockchain difficult to tamper with?

In the blockchain system, two adjacent blocks are connected together through an encryption algorithm. Specifically, the data in the previous block will be encrypted into an encrypted digest and recorded in the next block. The generation of each block relies on the data recorded in the previous block to form a chain. Therefore, once a certain data is recorded in a certain block, it will be continuously encrypted and passed to each subsequent block in the form of a digest.

If you want to tamper with the data in a historical block, it will cause the data in all subsequent blocks to change. However, since subsequent blocks have been recorded by all nodes, they need to be modified jointly by all nodes, which requires the consent of more than half of the nodes. Other nodes in the network will consider tampering with data as evil and will not agree to the tampering.

But if more than half of the nodes in the network are controlled by perpetrators who want to tamper with data, then data tampering will occur. This is also the fragility of the blockchain system, which is based on the assumption that "the majority of the group is always upright." Therefore, in the blockchain system, if someone controls more than half of the nodes, he can tamper with the data in the blockchain to make profits for himself.

This is why the data in the blockchain is difficult to be tampered, but it is also possible to be tampered with.

Why is the blockchain open and transparent?

The foundation of blockchain technology is open source. The data of the blockchain is open to everyone. Everyone can query the data in the blockchain through the public interface and develop related applications. , so the entire blockchain system is open and transparent.

For more information about the characteristics of blockchain, please refer to the chapter "What is the Impossible Triangle of Blockchain".