A block header is a part of a block in a blockchain.
It contains metadata about the block, such as the block's hash, the timestamp, the difficulty, and the Merkle root. The block header is used to verify the integrity of the block and to link it to the previous block in the blockchain.
Block Header Structure
The block header has the following structure:
Version: The version number of the block.
Prev_Hash: The hash of the previous block in the blockchain.
Merkle_Root: The Merkle root of the transactions in the block.
Timestamp: The timestamp of the block.
Nonce: A random number used to solve the proof-of-work puzzle.
Target: The target hash that the nonce must be less than or equal to in order to solve the proof-of-work puzzle.
Block Header Validation
When a miner finds a block, they must first validate the block header. This involves verifying that the following conditions are met:
The block header must be a valid size.
The timestamp must be greater than the timestamp of the previous block.
The Merkle root must be the root of the Merkle tree of the transactions in the block.
The nonce must be less than or equal to the target hash.
If any of these conditions are not met, the block is invalid and will not be accepted by the network.
Block Header Linking
The block header is used to link blocks together in a blockchain. The hash of each block header is stored in the next block header. This creates a chain of blocks, where each block is linked to the previous block.
The block header linking mechanism ensures that the blockchain is immutable. Once a block is added to the blockchain, it cannot be changed without changing all of the blocks that come after it. This makes the blockchain a secure and tamper-proof way to store data.