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CS-364: Introduction to Cryptography and Network Security LAB Code must be written in C and well commented

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CS-364: Introduction to Cryptography and Network Security LAB Code must be written in C and well commented. Code should be 100 percent plagiarism free, and should not be shared with anyone.

LAB Assignment III

Implement the encryption as well as the decryption of AES′ block cipher.
Plaintext Ciphertext
Key-scheduling(128bit key)
k
0 k1 k8 k9 k10
π
AES ':
SubBytes '
ShiftRows
MixColumn'
π
AES ':
SubBytes '
ShiftRows
MixColumn'
π'
AES ':
SubBytes '
ShiftRows
Round=1 Round=9 Round=10
Figure 1: AES′
Consider the Subbyte function Sub (given in Figure 2) of AES. Using the Sub (Figure 2) define a Subbyte′
112 Cryptography: Theory and Practice
TABLE 4.5: The AES S-box
Y
X 0 1 2 3 4 5 6 7 8 9 A B C D E F
0 63 7C 77 7B F2 6B 6F C5 30 01 67 2B FE D7 AB 76
1 CA 82 C9 7D FA 59 47 F0 AD D4 A2 AF 9C A4 72 C0
2 B7 FD 93 26 36 3F F7 CC 34 A5 E5 F1 71 D8 31 15
3 04 C7 23 C3 18 96 05 9A 07 12 80 E2 EB 27 B2 75
4 09 83 2C 1A 1B 6E 5A A0 52 3B D6 B3 29 E3 2F 84
5 53 D1 00 ED 20 FC B1 5B 6A CB BE 39 4A 4C 58 CF
6 D0 EF AA FB 43 4D 33 85 45 F9 02 7F 50 3C 9F A8
7 51 A3 40 8F 92 9D 38 F5 BC B6 DA 21 10 FF F3 D2
8 CD 0C 13 EC 5F 97 44 17 C4 A7 7E 3D 64 5D 19 73
9 60 81 4F DC 22 2A 90 88 46 EE B8 14 DE 5E 0B DB
A E0 32 3A 0A 49 06 24 5C C2 D3 AC 62 91 95 E4 79
B E7 C8 37 6D 8D D5 4E A9 6C 56 F4 EA 65 7A AE 08
C BA 78 25 2E 1C A6 B4 C6 E8 DD 74 1F 4B BD 8B 8A
D 70 3E B5 66 48 03 F6 0E 61 35 57 B9 86 C1 1D 9E
E E1 F8 98 11 69 D9 8E 94 9B 1E 87 E9 CE 55 28 DF
F 8C A1 89 0D BF E6 42 68 41 99 2D 0F B0 54 BB 16
in row X and column Y is πS(XY). The array representation of πS is presented in
Table 4.5.
In contrast to the S-boxes in DES, which are apparently “random” substitutions, the AES S-box can be defined algebraically. The algebraic formulation of the
AES S-box involves operations in a finite field (finite fields are discussed in detail
in Section 7.4). We include the following description for the benefit of readers who
are already familiar with finite fields (other readers may want to skip this description, or read Section 7.4 first): The permutation πS incorporates operations in the
finite field
F
28 = Z2[x]/(x8 + x4 + x3 + x + 1).
Let FIELDINV denote the multiplicative inverse of a field element; let BINARYTOFIELD convert a byte to a field element; and let FIELDTOBINARY perform the
i
Figure 2: AES-Subbytes

Here +, ∗ are the two binary operations of the field F2[x]/ < x8 + x4 + x3 + x + 1 >.
Consider the following matrix M (given in Equation (2), in integer) instead of original mixcolumn matrix
1
of AES.
M =
????
1 4 4 5
5 1 4 4
4 5 1 4
4 4 5 1
????
(2)
The inverse of M is given in Equation (3) (in integer).
M-1 =
????
165 7 26 115
115 165 7 26
26 115 165 7
7 26 115 165
????
(3)
Using M we will perform our Mixcolumn′ operation. We will use the same key-scheduling as in AES-128
encryption algorithm. With this setup implement 10 rounds of AES′. The pictorial design of AES′ is
given in Figure 1.
1. Input (scanf): plaintext of 128 bits. Input will be 16 hexadecimal e.g., a1 12 ...ca 45 ec
2. Input (scanf): key of 128 bits: Input will be 16 hexadecimal e.g., b1 32 ...ef 3a cb
3. Output (printf): encrypt the plaintext using the encryption algorithm of AES′ and print the ciphertext of 128 bits: Output will be 16 hexadecimal.
4. Output (printf): decrypt the generated ciphertext using the decryption algorithm of AES′ and print
the decrypted text of 128 bits: Output will be 16 hexadecimal.
If your code is correct the output in item (4) will match with input in item (1) for all possible random
inputs in item (1) and (2).
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