Cryptography

Given the following S-Boxes:
S1 = [ 15 10 2 5
           8 4 11 6
           1 0 14 7
           9 3 12 13 ];
S2=  [ 4 0 15 10
           8 9 7 13
           5 1 6 11
           2 3 14 12 ];

Implement the following 16 bit cipher:

Plain text:

Key: P = [a₁ a₂ a₃ a₄] where a₁..a₄ are 4 bit each

K = [k₁ k₂ k₃ k₄] where k₁..k₄ are 4 bit each

Cipher text: C = E(p) = [ S₁(a₂⊕k₁) S₂(a₄⊕_k3) S₁(a₁⊕k₂) S₂(a₃⊕k₄) ]

Example: P = [1000 1100 1101 0110], K = [0001 0011 0010 1111]

C = [S1(1101) S2(0100) S1(1011) S2(0010 ] = [6 0 12 5]

= [0110 0000 1100 0101]

1. Draw a chart which shows the relation between P, C, and K according to this cipher.

2. Implement the above mentioned cipher and calculate the cipher text for the plaintexts provided in Appendix I and the key provided in Appendix II.

3. Measure the avalanche effect for the encryption algorithm using the provided plaintexts. Change 1 bit in the input and calculate the % of how many bits are changed in the cipher text. Repeat this for the provided 10 plaintext inputs; this will give 10 x 16 rounds. Calculate the average avalanche effect.

4. Suggest a change to the encryption algorithm to enhance the avalanche effect. Repeat 3 and comment on your finding.

Attachment:- Appendix.rar