What is a Block

Blockchain is a chain-like storage structure formed by individual blocks connected in the order of their respective creation times. A block is the basic data storage unit within this structure.

What is blockchain? What are its characteristics? Please refer to the section “What is Blockchain.”

A block, as the basic structural unit in the blockchain, consists of a “block header” containing the block’s identity information and a “block body” containing database information. Compared to traditional database structures, the block body is similar to the specific content of each page in a database, while the block header is similar to the page number used to locate the data.

What is a block header? What is a hash function?

The block header mainly contains an encrypted summary of all data from the previous block, the creation time of the current block, and an encrypted summary of the block body.

An encrypted summary is generated using a commonly used one-way encryption algorithm in the blockchain field, which we generally call a “hash algorithm” or “hash function” (Hash Function). Its operation is similar to summarizing given content into a digest. It is called a one-way encryption algorithm because, when we know all the data contained in the previous block, we can easily generate the digest. However, if we only have the digest, it is very difficult to accurately deduce all the data of the previous block. The value generated from a given data segment through a hash algorithm is called the “hash value” (Hash Value) of that data.

To learn more about the principles, techniques, and operation of hash algorithms, please refer to Investopedia.

Through encryption by hash algorithms, each subsequently generated block always depends on the data of the previous block to generate the block header. This enables the blockchain to form a chain-like structure where blocks are linked end-to-end. Additionally, once data is recorded in a block, starting from the next block, it will be continuously combined with other data and encrypted into new hash values, recorded in subsequent blocks. This method also enhances the difficulty of tampering with data on the blockchain.

Remember when we mentioned that “individual blocks are connected in the order of their respective creation times” when introducing blockchain? This statement is not entirely accurate. Blocks are actually linked through hash algorithms and the block header structure. However, since blocks generated later in time always depend on the data of earlier blocks, an indirect chronological order is formed.

What is a “parent block”? What is a “genesis block”?

In the blockchain field, the block that contains the hash-encrypted previous block in its block header is called the “parent block.” When a blockchain has not yet produced its first block, there is no parent block, and subsequent blocks cannot be generated. At this point, the founding team of the blockchain usually creates the first block, which does not contain any hash of a parent block. This block is called the “genesis block.” The creation of the genesis block generally signifies the official start of the blockchain’s operation. The data in the genesis block will be encrypted and recorded in all subsequent blocks of the blockchain.

For example: On January 3, 2009, Satoshi Nakamoto generated the genesis block of the Bitcoin network on a server located in Helsinki, Finland, marking the official birth of the Bitcoin network. Satoshi Nakamoto left a message on this block: “The Times 03/Jan/2009 Chancellor on brink of second bailout for banks.”