The Blockchain

The blockchain is a chronological order of blocks that are carrying transaction data. Each block is uniquely identifiable by its block hash, which is a unique hash value that corresponds to exactly the data the block is carrying, and if any data within a block is changed, the block would get a new hash value. We’ll subsequently see that this behavior is forming a change-sensitive structure that guarantees a tamper-proof ledger since any corrupted data will invalidate the whole blockchain. According to Antonopoulos (2014)Andreas M. Antonopoulos. Mastering Bitcoin: Unlocking Digital Cryptocurrencies. Sebastopol, CA, 2014. O’Reilly Media., we can define a blockchain data structure as follows:

Blockchain data-structure

“The blockchain data-structure is an ordered, back-linked list of blocks of transactions.”

Hence, blocks of a blockchain contain a reference to the previous block in the chain, which is called the parent block. The identification of a block occurs uniquely by a hash on its header. Thus, each block can be linked to its previous block by referencing the parent block’s hash. Every block includes this hash reference in its data structure, storing it in the previous block hash field in the block header, as shown in this figure. This means that each block stores the hash of its parent block inside its own block header.

Figure 1