Use the block cipher Fkx in Example 351 to encipher the plai

Use the block cipher F_k(x) in Example 3.5.1 to encipher the plaintext AH by using the 8-bit binary ASCII representation of the letters, subdividing into 4-bit blocks, and using the key k = 001.

Example 3.5.1 Let S(x) be a function defined by the following table 1x2x3 s(x1x2x3) 011 10 100 01 101 00 110 10

Solution

A and H in binary Ascii.

A = 65 = 01000001

H = 72 = 01001000.

AH in binary ASCII and subdivided into 4-bit blocks is 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0. Enciphering with k = 001 gives 0, 1, 1, 0, 0, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 0.

01100011 = 99 = c

01101100 = 108 = l

AH is encrypted to cl.