Crypto Core Education

What is a hash collision and why does it matter?

A hash collision happens when two different inputs produce the same output from a hash function, even though a hash is meant to map every input to a unique fixed-length fingerprint. It matters because blockchains rely on hashes to link blocks, verify data, and secure proofs, so a practical collision would let someone substitute fraudulent data that still matches a trusted hash. Modern functions like SHA-256 are designed to make collisions computationally infeasible to find. For example, if you could forge a transaction with the same hash as a real one, the integrity of the chain would break, which is why collision resistance is fundamental.