Candidate Block

What Is a Candidate Block?

A candidate block is a block that a mining node (miner) attempts to mine to get a block reward. As a result, a candidate block can be thought of as a momentary block that would be validated or deleted by the network. Miners fight with one another to validate the upcoming block and add it to the blockchain, but before that, they must construct a candidate block to compete. 

Diving Deep Into the Concept of a Candidate Block

Miners build candidate blocks by collecting and sorting many unprocessed transactions from the memory pool. The transactions then are hashed to construct a Merkle tree structure, from which a Merkle root is eventually produced (or root hash). 

The Merkle root is a singular hash that reflects all previous hashes in that tree and thus all transactions in that specific block. The root hash, the preceding block's hash, and a random integer called nonce is then appended to the block's header. 

The miner then hashes the block header, producing an output objected on those components (root hash, preceding block's hash, and nonce) and a few others. The outcome is the block hash, which will act as the freshly formed block's unique identification (candidate block).

To be considered genuine, the output (block hash) must begin with a specific number of zeros (fewer than a target value defined by the protocol). This implies that the mining procedure is focused on repeated attempts (trial and error), as the mining nodes must conduct a plethora of hashing functions with varying nonce values till a valid block hash is achieved. 

Finally, the block hash generated proves that the miner completed his task (hence Proof of Work). When a miner discovers a suitable block hash, their candidate block is broadcasted to the rest of the network's nodes, who validate the hash's legitimacy. 

The candidate block will be added to the blockchain if everything checks up. At this moment, each validating node's version of the blockchain data is updated to reflect the most recently mined block, and the miner receives the block reward.