Hajufunktsioonide

Hajufunktsioonide, also known as hash functions, are mathematical algorithms that take an input of arbitrary size and produce an output of a fixed size. This output is commonly referred to as a hash value, hash code, digest, or simply hash. The key properties of a good hash function include determinism, meaning the same input will always produce the same output, and efficiency, meaning the function can be computed quickly.

Hash functions are fundamental in computer science and have a wide range of applications. One of the primary uses is in data integrity checks. By comparing the hash of a file or message with a known, trusted hash, one can verify if the data has been altered or corrupted. This is often seen in software downloads, where a provided hash allows users to confirm the integrity of the downloaded files.

Another significant application is in data structures, particularly hash tables. Hash tables use hash functions to map keys to indices in an array, allowing for very fast average-case time complexity for insertion, deletion, and lookup operations. Cryptography also heavily relies on hash functions for secure password storage, digital signatures, and message authentication codes. In these cryptographic contexts, properties like collision resistance (it being computationally infeasible to find two different inputs that produce the same hash) and preimage resistance (it being computationally infeasible to find an input that produces a given hash) are crucial. Examples of widely used hash functions include MD5 (though now considered insecure for many cryptographic purposes), SHA-1, and SHA-256.