Assignment
Given the following S-Boxes:
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S1= [ 15 10 2
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5
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8 4 11
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6
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1 0 14
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7
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9 3 12
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13
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];
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S2= [ 4 0 15
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10
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8 9 7
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13
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5 1 6
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11
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2 3 14
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12
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];
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Implement the following 16 bit cipher:
Plain text:
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Plain text:
Key:
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P = [a1 a2 a3 a4] where a1..a4 are 4 bit each
K = [k1 k2 k3 k4] where k1..k4 are 4 bit each
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|
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Cipher text:
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C = E(p) = [ S1(a2⊕k1) S2(a4⊕k3) S1(a1⊕k2)
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S2(a3⊕k4)
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]
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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.
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 Key
1010 0010 0011 1010