Ferguson, Niels; Lucks, Stefan; Schneier, Bruce; Whiting, Doug; Bellare, Mihir; Kohno, Tadayoshi; Callas, Jon; Walker, Jesse (October 1, 2010), The Skein Hash Function Family(PDF), archived from the original(PDF) on 2014-08-24 The paper in which Threefish was introduced.
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Ferguson, Niels; Lucks, Stefan; Schneier, Bruce; Whiting, Doug; Bellare, Mihir; Kohno, Tadayoshi; Callas, Jon; Walker, Jesse (October 1, 2010), The Skein Hash Function Family(PDF), archived from the original(PDF) on 2014-08-24 The paper in which Threefish was introduced.