Mastering Bitcoin, 3rd Edition

Chapter 11. The Blockchain

The blockchain is the history of every confirmed Bitcoin transaction. It’s what allows every full node to independently determine what keys and scripts control which bitcoins. In this chapter, we’ll look at the structure of the blockchain and see how it uses cryptographic commitments and other clever tricks to make every part of it easy for full nodes (and sometimes lightweight clients) to validate.

The blockchain data structure is an ordered, back-linked list of blocks of transactions. The blockchain can be stored as a flat file or in a simple database. Blocks are linked “back,” each referring to the previous block in the chain. The blockchain is often visualized as a vertical stack, with blocks layered on top of each other and the first block serving as the foundation of the stack. The visualization of blocks stacked on top of each other results in the use of terms such as “height” to refer to the distance from the first block, and “top” or “tip” to refer to the most recently added block.

Each block within the blockchain is identified by a hash, generated using the SHA256 cryptographic hash algorithm on the header of the block. Each block also commits to the previous block, known as the parent block, through the “previous block hash” field in the block header. The sequence of hashes linking each block to its parent creates a chain going back all the way to the first block ever created, known as the genesis block.

Although a block has just one parent, ...