In a block cipher, diffusion can be accomplished through:

A.
Nonlinear S-boxes

B.
Substitution

C.
Permutation

D.
XORing

Explanation:
Diffusion is aimed at obscuring redundancy in the plaintext by spreading the effect of the
transformation over the ciphertext. Permutation is also known as transposition and operates by
rearranging the letters of the plaintext. *Answer substitution is used to implement confusion in a
block cipher. Confusion tries to hide the relationship between the plaintext and the ciphertext. The
Caesar cipher is an example of a substitution cipher. * XORing is incorrect since XORing, for example,
as used in a stream cipher, implements confusion and not diffusion. Similarly, nonlinear S-boxes
implement substitution. In DES, for example, there are eight different S-boxes that each has an input
of 6 bits and an output of 4 bits. Thus, nonlinear substitution is effected.