Data Science: Hash Function (Definition)

"A function that maps a set of keys onto a set of addresses." (S. Sumathi & S. Esakkirajan, "Fundamentals of Relational Database Management Systems", 2007)

"A function that maps a string of arbitrary length to a fixed size value in a deterministic manner. Such a function may or may not have cryptographic applications." (Mark S Merkow & Lakshmikanth Raghavan, "Secure and Resilient Software Development", 2010)

[cryptographic hash function:] "A function that takes an input string of arbitrary length and produces a fixed-size output for which it is unfeasible to find two inputs that map to the same output, and it is unfeasible to learn anything about the input from the output." (Mark S Merkow & Lakshmikanth Raghavan, "Secure and Resilient Software Development", 2010)

[one-way hash function:] "A hash function for which it is computationally unfeasible to determine anything about the input from the output." (Mark S Merkow & Lakshmikanth Raghavan, "Secure and Resilient Software Development", 2010)

"A function that operates on an arbitrary-length input value and returns a fixed-length hash value." (Oracle, "Database SQL Tuning Guide Glossary", 2013)

[one-way hash:] "A one-way hash is an algorithm that transforms one string into another string (a fixed-length sequence of seemingly random characters) in such a way that the original string cannot be calculated by operations on the one-way hash value (i.e., the calculation is one way only). One-way hash values can be calculated for any string, including a person’s name, a document, or an image. For any input string, the resultant one-way hash will always be the same. If a single byte of the input string is modified, the resulting one-way hash will be changed and will have a totally different sequence than the one-way hash sequence calculated for the unmodified string. One-way hash values can be made sufficiently long (e.g., 256 bits) that a hash string collision (i.e., the occurrence of two different input strings with the same one-way hash output value) is negligible." (Jules H Berman, "Principles of Big Data: Preparing, Sharing, and Analyzing Complex Information", 2013)

"A hash function is an algorithm that maps from an input, for example, a string of characters, to an output string. The size of the input can vary, but the size of the output is always the same." (Dan Sullivan, "NoSQL for Mere Mortals®", 2015)

[one-way hash:] "Cryptographic process that takes an arbitrary amount of data and generates a fixed-length value. Used for integrity protection." (Adam Gordon, "Official (ISC)2 Guide to the CISSP CBK" 4th Ed., 2015)

"A function that takes as input the key of an element and produces an integer as output" (Nell Dale et al, "Object-Oriented Data Structures Using Java" 4th Ed., 2016)

"encryption methods that use no keys." (Manish Agrawal, "Information Security and IT Risk Management", 2014)

"A function that operates on an arbitrary-length input value and returns a fixed-length hash value." (Oracle, "Oracle Database Concepts")