Upper Bounds on Differential Characteristics in Twofish

N. Ferguson

August 17, 1998

ABSTRACT: In our original paper, the Twofish block cipher was introduced, and initial estimates of an upper bounds on the probability of a 12-round differential were given. These results used an imperfect model of Twofish. We present an improved model, and show that any 12-round differential characteristic has a probability of at most 2^-102.8.

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