The word "hash function" is spelled as /hæʃ ˈfʌŋkʃən/ in IPA phonetic transcription. The first syllable is pronounced as "ha-sh" with a short "a" sound followed by the "sh" sound. The second syllable is pronounced as "fun" with a short "u" sound followed by "k-shuhn" with a schwa sound for the "u" and "n" and the "sh" sound. The spelling "hash" comes from the word "hacker's jargon" and refers to the representation of data in a small fixed-size format.
A hash function is a mathematical algorithm that takes an input (usually referred to as the "message") and produces a fixed-size string of characters, which is generally a sequence of digits and letters. The output, known as the "hash value" or "hash code," is unique to the specific input data and is referred to as a digital fingerprint.
The key characteristics of a hash function include the ability to efficiently compute the hash value for any given input, producing a fixed-length output regardless of the input size or complexity. Additionally, a good hash function should have a low probability of producing the same hash value for different inputs, a property known as "collision resistance."
Hash functions find various applications in computer science and cryptography. They are often used to store and retrieve data efficiently. For instance, hash functions can transform large amounts of data into compact hash values, which can be used as an index or key for data storage and retrieval systems.
Hash functions are also essential in ensuring data integrity and security. They can be used to check whether data has been modified or tampered with, as even a slight change in the input will result in a completely different hash value. Additionally, hash functions are employed in digital signatures, password storage, and data encryption algorithms to safeguard information.
The word "hash" in "hash function" comes from the term "hashing", which originates from the verb "to hash". The term "hash" in this context is believed to derive from the English word "hatch" or "hack", meaning to chop or mangle things roughly. The term "hashing" was first used in the 1950s by Hans Peter Luhn, an IBM scientist, to refer to the technique of transforming data (such as a key) into a fixed-size numerical value or "hash code". Over time, "hash function" became the common term for a mathematical function that performs this transformation.