An information processing device comprises: a non-linear transformation unit that takes a k/2-number of odd-numbered string data Bi (i=1, 3, . . . , k−1), k being an even number not smaller than 6, out of a k-number of string data {B1, B2, . . . , Bk}, as intermediate data Wi, and that XORs data transformed from the odd-numbered string data Bi based on a bijective F-function, in which an as-transformed value is determined responsive to a value of key data, and even-numbered string data Bi+1, to give intermediate data Wi+1; and a permutation unit that permutes the intermediate data {W1, W2, . . . , Wk} by the data {B1, B2, . . . , Bk}; in so permuting the intermediate data, the permutation unit permuting odd-numbered data by even-numbered data and permuting even-numbered data by odd-numbered data; the permutation unit not permuting Wi+1 by B((i+1)mod—k)+1, where i=0, 1, 2, . . . , k−1 and x mod y is a remainder left after dividing x by y, and not permuting Wi+1 by B((i+k-1)mod—k)+1.