Block Header

Block Header Explained in Simple Terms

A block header is like the identification card of a blockchain block.

Instead of storing all transaction details, the block header contains summarized information that miners use during mining. It connects the block to the previous block and helps secure the blockchain.

When miners perform mining calculations, they repeatedly hash the block header while changing the nonce value until they find a valid hash that meets the network difficulty requirement.

How Block Header Works

The block header is created before mining begins and is included in every block.

Here’s how the process works:

1. Previous Block Hash
   The header stores the hash of the previous block, linking blocks together into a blockchain.

2. Merkle Root
   The Merkle Root summarizes all transactions included in the block.

3. Timestamp
   The current block creation time is added.

4. Difficulty Target
   The network difficulty determines how difficult it is to find a valid block hash.

5. Nonce Field
   Miners continuously change the nonce value while hashing the block header.

6. Mining Process
   Miners repeatedly hash the block header using Double SHA-256 until the resulting hash is lower than the target difficulty.

The Bitcoin mining condition is:

Example of a Block Header

A Bitcoin miner creates a candidate block containing:

• transaction data

• coinbase transaction

• previous block hash

The miner then generates the block header and starts hashing it billions of times per second using ASIC miners.

Each time the nonce changes:

• the block header hash changes

• the miner gets a new chance to find a valid solution

Once a valid block hash is discovered, the block is broadcast to the network for verification.