What is the role of a compression function in a hash function?

A compression function in a hash function takes an input block of data and reduces it to a fixed-size output, typically producing a hash value. This function processes the input in chunks, combining them with previously computed outputs to ensure that even small changes in the input result in significantly different hash values. Compression functions help maintain efficiency and security, allowing for the creation of unique identifiers for variable-length inputs while minimizing the risk of collisions. Overall, they are essential for ensuring the integrity and reliability of hash functions.