s) Below is a substitution table (S-box) expressed in octal (base-8 that it repl

Question

s) Below is a substitution table (S-box) expressed in octal (base-8 that it replaces digits with one digit, size of the re cutting the 1 3 4 5 6 7 5 0 3 6 7 1 2. I 3 6 1 5 2 7 4 4 1 2 3 6 0 7 4 0 7 1 3 5 1 2 6 5 4 3 7 3 5 4 0 2 6. 0 5 7 2 4 6 1 6 7 4 1 3 5 0 table to replace each of the following 8-digit values with 4- digit of each pair to index the row and the second to index 2 15 67 45 54 65 01 e S-DES to encrypt the plaintext block 10100101 11 by hand. Show your work, giving the values of K1 e output of each step

Explanation / Answer

5.

a. 24 52 15 67 = 10 11 12 13 14

b. 00 24 45 54 = 24 33 42 51

c. 37 73 65 01 = 25 16 36 45

6.

1. Apply IP to TO.

2. Apply /fci to the output from step 1. (This is round 1.)

3. Apply SW to the output of step 2.

4. Apply /fc 2 to the output of step 3. (This is round 2.)

5. Apply IP-I to the output of step 4.

1. Pio(A:) = 1000010111.

2. LSl(lOOOO) = (00001) and LSl(lOlll) = (01111).

3. P8(0000101111) = (00101111) = ki.

4. LS2(00001) = (00100) and LS2(01111) = (11101) {applying LS2 to the output of step 2) .

5. P8(0010011101) = (11101010) = k 2 {applying P8 to the output of step 4)-

Now we encrypt as follows. First we calculate IP(m) = (01110100).

Then we need to calculate the round function for the first round (01110100) = (L(OlllOlOO) 0F(R(OlllOlOO),fci),R(OlllOlOO)). FFe do this as follows.

1. EP(OIOO) = (00101000).

2. EP(OIOO) © fci = (00101000) © (00101111) = (00000111).

3. So(OOOO) = (01) and Si(Olll) = (11).

4. P4(0111) = (1110) = F(R(01110100),fci).

5. L(OlllOlOO) © F(R(01110100), fci) = (0111) © (1110) = (1001).

6. /fei (01110100) = (10010100). Now we apply the switch function, SW(IOOIOIOO) = (01001001).

Now we canverify the second round, namely, /fe,(01001001) = (L(01001001)®E(R(01001001),fc2),R(01001001)) = (01101001).

Last, we apply the inverse of the initial permutation, IP~^ (01 101001) = (00110110), which is the ciphertext.

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