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Cryptographic hash function

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In cryptography,a cryptographic hash function is a transformation thattakes an input and returns a fixed-size string, which is called thehash value. Hash functionswith this property are used for a varietyof computational purposes, including cryptography. The hash value is aconcise representation of the message or document from which it wascomputed. Cryptographic hash functions are used to do message integritychecks and digital signatures in variousinformation security applications,such as authentication andmessage integrity.

A hash function takes a string(or 'message') of any length as input andproduces a fixed length string as output, sometimes termed a message digestor a digital fingerprint. A hash value (also called a "digest" or a"checksum") is a kind of "signature" for a stream of data that representsthe contents. One analogy that explains the role of the hash function wouldbe the "tamper-evident" seals used on a software package.

In various standards and applications, the two most commonly used hashfunctions are MD5 and SHA-1.In 2005, security flaws were identified inboth algorithms. In 2007 the NationalInstitute of Standards and Technology announced a contest to design a hash function which will begiven the name SHA-3 and be the subject of aFIPS standard.