Definition
A pre-image is an input value that, when processed by a cryptographic hash function, produces a specific hash output. In formal terms, for a hash function H and a given digest y, a pre-image is any x such that H(x) = y. In blockchain and cryptographic protocols, pre-images are fundamental objects underlying security properties like pre-image resistance and are often treated as secret or hard-to-find values.
In Simple Terms
A pre-image is the original data that was fed into a hash function to create a particular hash. If you know the hash and the hash function, the pre-image is any piece of data that would generate exactly that hash when run through the function.
Context and Usage
Pre-images appear throughout blockchain and cryptographic system design as conceptual components in security arguments, protocol definitions, and commitment structures. They are referenced when discussing hash-based security assumptions, the hardness of reversing hash outputs, and the structure of data authenticated via hashing. Pre-images are central in formal treatments of hash-based constructions and in reasoning about the integrity and binding properties of hashed data within distributed systems.