| 3.1 In Section 3.1, under the subsection on the motivation for the Feistel cipher structure, it was stated that, for a block of n bits, the number of different reversible mappings for the ideal block cipher is 2n!. Justify. a. In that same discussion, it was stated that for the ideal block cipher, which allows all possible reversible mappings, the size of the key is n x 2 n bits. But, if there are 2 n! possible mappings, it should take log2 2 n! bits to discriminate among the different mappings, and so the key length should be log2 2 n!. However, log2 2n! reversible mappings, the size of the key is n x 2n bits. But, if there are 2n! possible mappings, it should take log2 2n! bits to discriminate among the different mappings, and so the key length should be log2 2n!. However, log2 2n! | |
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