Block Chain - Block Hashes

Block hashes play a critical role in ensuring the security and immutability of the blockchain. Each block in the blockchain contains a unique block hash, which serves as a digital fingerprint of that block. 

Hash Function

A cryptographic hash function is used to generate the block hash. This hash function takes an input (data) of any length and produces a fixed-length alphanumeric output, known as the hash value or hash code. It is designed in such a way that even a slight change in the input data will result in a completely different hash value.

Block Header

Each block in the blockchain has a block header that contains various pieces of information. The block header typically includes:

• Version Number: A number representing the version of the block.
• Previous Block Hash: The hash of the previous block in the blockchain. This links the blocks together, creating a chain.
• Merkle Root: A hash of all the transactions in the block, represented in a Merkle tree structure.
• Timestamp: The time when the block was created.
• Nonce: A random number used in the mining process to find a valid hash value.

Mining Process

Miners in the network compete to find a valid block hash for a new block. To do this, they adjust the value of the nonce in the block header and recompute the hash until they find a hash that meets a specific difficulty target. This target is set by the network and is adjusted periodically to maintain a consistent rate of block generation. The lower the difficulty target, the harder it is to find a valid hash.

Finding a Valid Hash

Miners repeatedly change the nonce and compute the hash of the block header until they find a hash value that is below the current difficulty target. This process is known as Proof of Work (PoW) mining. Finding a valid hash requires a considerable amount of computational power and is a probabilistic process. Miners compete to be the first one to find a valid hash for the next block.

Proof of Work

When a miner finds a valid hash, they broadcast the new block to the network, along with the valid proof of work. Other nodes in the network can easily verify that the proof of work is correct by recomputing the block hash with the given nonce and other block header information.

Block Addition

If the other nodes in the network confirm that the block's proof of work is valid, they add the new block to their copy of the blockchain. The block's hash becomes part of the next block's header as the "Previous Block Hash," effectively linking the blocks together in a chain.

Immutability

Since each block's hash depends on its content, including the hash of the previous block, any alteration to a block's data would change its hash and the subsequent blocks' hashes. This property ensures the security and immutability of the blockchain, as any attempt to modify a block would be evident and rejected by the network consensus.