Cryptographic hashing functions are extremely important with regard to security, integrity, and effectiveness of the technology of Blockchain. A cryptographic hash function is a deterministic one-way function, taking an input or "message" and giving a fixed-length string of characters, typically referred to as the "hash". A hash function must be deterministic: if a given input is provided, it will produce the same hash every time. They are also one-way functions, given a hash, it is computationally infeasible to compute its original input, which serves for the purpose of data security.
In Blockchain, the hash is done using such functions as SHA-256 (the hashing algorithm used in Bitcoin) to serve several purposes. The first is to preserve data integrity. If transactions are hashed and added to the blocks, if the data in the transaction is modified for tampering, this would result in a completely different hash. This makes both tasks of detecting tampering and leaving corroborative evidence of that tampering easier, as even a slight change in some data of a block results in the hash stored and that computed due to alteration differing.
Similarly, using hashes, blocks fit together in the Blockchain. Each block contains its predecessor's hash. Thus, an unbreakable "chain" is formed. Any alteration of a block by an attacker would break the hash continuity; thus, making them easy to detect. This chain-like arrangement guarantees that past data, once entered into the Blockchain, cannot be tampered with or deleted, and hence the old data is proved to be safe and protected.
Using hashing functions, PoW miners search in order to mine blocks. Miners compete against each other in solving cryptographic puzzles by seeking out a hash with certain properties; a process that may take enormous computing resources. For this reason, a malicious actor would encounter significant difficulty manipulating blocks due to the need for "re-mining" the altered block and all subsequent blocks.
Thus, cryptographic hash functions serve multiple purposes, including the security of blockchains in enabling them to become decentralized and tamper-proof.
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It is a great article of Cryptographic hashing functions and their significance in blockchain.
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