# Cryptographic Hash Function 1. The [[Cryptography|cryptographic]] hash function is a mathematical [[algorithm]] that takes a particular input which can be any kind of digital data be it a password or jpeg file and produces a single fixed length output. Some examples of different hash function algorithms are [[MD5]], MD4 or [[SHA-256]]. The last one is used in the [[Bitcoin Protocol]]. Main properties: (1) easy to compute [[Hash|hash]] value for any given message (2) infeasible to generate a message from its hash except by trying all possible input combinations(brute force attack) (3) infeasible to modify a message without changing the hash (4) infeasible to find two different messages with the same hash (5) deterministic so the same message always results in the same hash. Cryptographic hash functions have many information security applications, notably in [[Digital Signature|digital signatures]], message authentication codes (MACs), and other forms of authentication. They can also be used as ordinary hash functions, to index data in hash tables, for fingerprinting, to detect duplicate data or uniquely identify files, and as [[Checksum|checksums]] to detect accidental data corruption. 2. In their most basic sense, one can think of cryptographic hashes as digital avenues that help in the production of a fixed-size/unique [[hash]] value from a [[Transacton Input|transaction input]] that might be variable in its size function. 3. Cryptographic [[Hash|hashes]] produce a fixed-size and unique hash value from variable-size transaction input. The [[SHA-256|SHA-256]] computational algorithm is an example of a [[Cryptography|cryptographic]] hash. 5. A function that returns a unique fixed-length string. The returned string is unique for every unique input. Used to create a “digital ID” or “digital thumbprint” of an input string.