Any Encryption algorithm (like caesar cipher algorithm)should be used and implemented for the information given in the document.

Cryptography

Assignment

Given the following S-Boxes:

S1= [ 15        10            2          5

8          4          11        12

1          0          14        7

9          3          6          13        ];

S2= [   4          5          15        10

8          9          7          13

0           1          6          11

2          3          14        12        ];

Implement the following 16 bit cipher:

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

Key:                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]                   = [12 5 6 0]

                                                                                               = [1100 0101 0110 0000]

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 plaintext provided in Appendix I.

3. Measure the avalanche effect for the encryption algorithm using the provided plain text.

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.

Appendix I: Test Plain Text

1001 0100 0110 0110

0010 1001 1100 0010

0101 1100 1110 0010

1001 1100 0010 0111

1011 1101 1101 1111

0001 1101 0001 0011

1110 0001 1100 0011

0011 1110 0000 0010

0101 0011 1101 1011

1100 0010 0111 0100

Appendix II: Test Keys

0101 0100 1001 1100

1010 0010 0011 1010