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Extendable-output function
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<p>Extendable-output function (XOF) is an extension of the <a href="/facts/Cryptographic_hash/cuxkgbST">cryptographic hash</a> that allows its output to be arbitrarily long. In particular, the <a href="/facts/Sponge_construction/DA3BT6Ss">sponge construction</a> makes any <a href="/facts/Sponge_hash/DA3BT6Ss">sponge hash</a> 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). </p><p>The genesis of a XOF makes it <a href="/facts/Collision_resistance/8eBxsuHe">collision</a>, <a href="/facts/Preimage_resistance/dDktzjys">preimage</a> and <a href="/facts/Second_preimage/dDktzjys">second preimage</a> 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 <a href="/facts/Domain_separation_(cryptography)/VKFxzt5p">domain separation</a>). The examples of XOF include the algorithms from the <a href="/facts/Keccak/bA3BCp7K">Keccak</a> family: <a href="/facts/SHAKE128/bA3BCp7K">SHAKE128</a>, <a href="/facts/SHAKE256/bA3BCp7K">SHAKE256</a>, and a variant with higher efficiency, <a href="/facts/KangarooTwelve/bA3BCp7K">KangarooTwelve</a>. </p><p>XOFs are used as <a href="/facts/Key_derivation_function/3jL2jTTb">key derivation functions</a> (KDFs), <a href="/facts/Stream_cipher/BxU0aWmJ">stream ciphers</a>, <a href="/facts/Mask_generation_function/2KLvL81q">mask generation functions</a>. </p>