| 摘要 |
PROBLEM TO BE SOLVED: To provide a ciphering device which performs high and uniform diffusion while holding down a calculation cost. SOLUTION: A local small diffusion is performed by each of plural nonlinear conversion modules 2 arranged in parallel in each step, and then a large diffusion is performed over a block width by a diffusion module 3, and the local small diffusions are performed by the nonlinear conversion modules 2 again, and this operation is repeated in a prescribed number of steps. Further, the nonlinear conversion module 2 is composed by alternately arranging a nonlinear conversion module 4 and a diffusion module 5. Namely, it is structured as a nested SPN. The diffusion module 3 performs a linear conversion for spreading at least one bit state of an input data to a nonlinear conversion module group of the preceding step to at least one bit state of an input data to a nonlinear conversion module of the following step through plural operation routes.
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