Question

If the block size is ‘s’, how many affine transformations are possible ?

(a) 2^s (2^s-1)(2^s-1)(2^s-1^2)………(2^s-1^(s-1))

(b) 2^s (2^s-1)(2^s-2)(2^s-2^2)………(2^s-2^(s-2))

(c) 2^ss (2^s-1)(2^s-2)(2^s-2^2)………(2^s-2^(s-1))

(d) 2^s (2^s-1)(2^s-2)(2^s-2^2)………(2^s-2^(s-3))

This question was posed to me in final exam.

My doubt stems from Block Cipher Systems in portion Block Ciphers and the Data Encryption Standard of Cryptograph & Network Security

Answer 1

Correct choice is (c) 2^ss (2^s-1)(2^s-2)(2^s-2^2)………(2^s-2^(s-1))

To explain: 2^s (2^s-1)(2^s-2)(2^s-2^2)………(2^s-2^(s-1)) is the maximum number of affine transformations possible for a block size ‘s’ matrix.