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SipHash
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<p>SipHash is an <a href="/facts/Block_cipher/MJywAyfQ">add–rotate–xor</a> (ARX) based family of <a href="/facts/Pseudorandom_function/Y2PpjPeF">pseudorandom functions</a> created by Jean-Philippe Aumasson and <a href="/facts/Daniel_J._Bernstein/KQLuMRTx">Daniel J. Bernstein</a> in 2012,: 165 in response to a spate of <a href="/facts/Collision_attack/6aXFAMbW">"hash flooding"</a> <a href="/facts/Denial-of-service_attack/6nkoK02J">denial-of-service attacks</a> (HashDoS) in late 2011. </p><p>SipHash is designed as a <a href="/facts/Pseudorandom_function_family/Y2PpjPeF">secure pseudorandom function</a> and can also be used as a secure <a href="/facts/Message_authentication_code/mXxCP5Yl">message authentication code</a> (MAC). SipHash, however, is not a general purpose key-less <a href="/facts/Hash_function/rk6MlCt3">hash function</a> such as <a href="/facts/Secure_Hash_Algorithms/rm1nXcGc">Secure Hash Algorithms</a> (SHA) and therefore must always be used with a secret key in order to be secure. That is, SHA is designed so that it is difficult for an attacker to find two messages <i>X</i> and <i>Y</i> such that SHA(<i>X</i>) = SHA(<i>Y</i>), even though anyone may compute SHA(<i>X</i>). SipHash instead guarantees that, having seen <i>Xi</i> and SipHash(<i>Xi</i>, <i>k</i>), an attacker who does not know the key <i>k</i> cannot find (any information about) <i>k</i> or SipHash(<i>Y</i>, <i>k</i>) for any message <i>Y</i> ∉ {<i>Xi</i>} which they have not seen before. </p>