Block Hash

A block hash is a unique identifier assigned to each block within a blockchain. Typically represented as a long hexadecimal string, it is crucial for maintaining the blockchain’s integrity.

On Layer 1 Ethereum, this value is created by applying a cryptographic hash function called Keccak256 to the block header. The resulting hash is included in the block header of the subsequent block, forming a continuous chain of blocks, hence the term “blockchain.” Including the previous block’s hash in the subsequent block ensures the blockchain’s integrity and immutability because if any block is altered, its hash value changes, breaking the link to subsequent blocks and invalidating them.

In Pheasant Network’s optimistic bridge protocol, block hashes play a crucial role during a special period known as the challenge period. In optimistic bridges, transactions are assumed valid by default and are tentatively processed. However, they must undergo a challenge period, during which, anyone who finds a transaction suspicious can contest its validity by presenting evidence known as fraud proof.

This fraud proof must include the block hash of the block containing the suspicious transaction so that the settlement layer, which has the ultimate authority to judge transaction validity in the event of a dispute, can accurately identify and scrutinize the transaction. The inclusion of the block hash ensures that the specific transaction in question can be located and verified against the data on Layer 1, thereby maintaining the integrity and security of the network.