What Is a Preimage Attack in Cryptography?

A preimage attack is a cryptographic attack where the goal is to find an input (the preimage) that produces a specific, known hash output. It targets the one-way property of a hash function, which is designed to be irreversible.

If successful, it compromises the security of systems like password storage or blockchain transaction integrity. A strong hash function must be resistant to this attack, meaning finding the input is computationally infeasible.

This is also known as a first-preimage resistance failure.