Extendable-output function: Difference between revisions

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'''Extendable-output function''' ('''XOF''') is an extension{{sfn|Peyrin|Wang|2020|p=7}} of the [[cryptographic hash]] that allows its output to be arbitrarily long. In particular, the [[sponge construction]] makes any [[sponge hash]] a natural XOF: the squeeze operation can be repeated, and the regular hash functions with a fixed-size result are obtained from a sponge mechanism by stopping the squeezing phase after obtaining the fixed number of bits).{{sfn | Mittelbach | Fischlin | 2021 | p=526}}

The genesis of a XOF makes it [[Collision resistance|collision]], [[Preimage resistance|preimage]] and [[second preimage]] resistant. Technically, any XOF can be turned into a cryptographic hash by truncating the result to a fixed length (in practice, hashes and XOFs are defined differently for [[Domain separation (cryptography)|___domain separation]]{{sfn|Dworkin|2014|p=3}}). The examples of XOF include the algorithms from the [[Keccak]] family: [[SHAKE128]], [[SHAKE256]], and a variant with higher efficiency, [[KangarooTwelve]].{{sfn|Peyrin|Wang|2020|p=7}}

XOFs are used as [[key derivation function]]s (KDFs), [[stream cipher]]s,{{sfn|Peyrin|Wang|2020|p=7}} [[mask generation function]]s.{{sfn|Perlner|2014|p=4}}