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prac-7.py
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prac-7.py
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def permute(k, arr):
return ''.join(k[i - 1] for i in arr)
def hex2bin(s):
return bin(int(s, 16))[2:].zfill(64)
def bin2hex(s):
return hex(int(s, 2))[2:].upper().zfill(16)
def left_shift(k, shifts):
return k[shifts:] + k[:shifts]
def key_schedule(key):
key = hex2bin(key)
key_permuted = permute(key, [
57, 49, 41, 33, 25, 17, 9, 1,
58, 50, 42, 34, 26, 18, 10, 2,
59, 51, 43, 35, 27, 19, 11, 3,
60, 52, 44, 36, 28, 20, 12, 4
])
left = key_permuted[:28]
right = key_permuted[28:]
shifts = [1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1]
round_keys = []
for shift in shifts:
left = left_shift(left, shift)
right = left_shift(right, shift)
combined = left + right
round_key = permute(combined, [
14, 17, 11, 24, 1, 5,
3, 28, 15, 6, 21, 10,
23, 19, 12, 4, 26, 8,
16, 7, 27, 20, 13, 2,
41, 52, 31, 37, 47, 55,
30, 40, 51, 45, 33, 48,
44, 49, 39, 56, 34, 53,
46, 42, 50, 36, 29, 32
])
round_keys.append(round_key)
return round_keys
def sbox_lookup(sbox, row, col):
return sbox[row][col]
def feistel_function(right, round_key):
expansion_permutation = [
32, 1, 2, 3, 4, 5,
4, 5, 6, 7, 8, 9,
8, 9, 10, 11, 12, 13,
12, 13, 14, 15, 16, 17,
16, 17, 18, 19, 20, 21,
20, 21, 22, 23, 24, 25,
24, 25, 26, 27, 28, 29,
28, 29, 30, 31, 32, 1
]
sboxes = [
[
[14, 4, 13, 1, 2, 15, 11, 8, 3, 10, 6, 12, 5, 9, 0, 7],
[0, 15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8],
[4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0],
[15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13]
],
# ... (complete all S-boxes)
]
right_expanded = permute(right, expansion_permutation)
xor_result = ''.join(str(int(b) ^ int(k)) for b, k in zip(right_expanded, round_key))
sbox_output = ""
for i in range(8):
row = int(xor_result[i * 6] + xor_result[i * 6 + 5], 2)
col = int(xor_result[i * 6 + 1:i * 6 + 5], 2)
sbox_value = sbox_lookup(sboxes[i], row, col)
sbox_output += bin(sbox_value)[2:].zfill(4)
return permute(sbox_output, [
16, 7, 20, 21,
29, 12, 28, 17,
1, 15, 23, 26,
5, 18, 31, 10,
2, 8, 24, 14,
32, 27, 3, 9,
19, 13, 30, 6,
22, 11, 4, 25
])
def des_encrypt(plaintext, key):
round_keys = key_schedule(key)
plaintext = hex2bin(plaintext)
initial_permutation = [
58, 50, 42, 34, 26, 18, 10, 2,
60, 52, 44, 36, 28, 20, 12, 4,
62, 54, 46, 38, 30, 22, 14, 6,
64, 56, 48, 40, 32, 24, 16, 8,
57, 49, 41, 33, 25, 17, 9, 1,
59, 51, 43, 35, 27, 19, 11, 3,
61, 53, 45, 37, 29, 21, 13, 5,
63, 55, 47, 39, 31, 23, 15, 7
]
plaintext = permute(plaintext, initial_permutation)
left, right = plaintext[:32], plaintext[32:]
for round_key in round_keys:
temp = right
right = ''.join(str(int(left[i]) ^ int(feistel_function(temp, round_key)[i])) for i in range(32))
left = temp
combined = left + right
final_permutation = [
40, 8, 48, 16, 56, 24, 64, 32,
39, 7, 47, 15, 55, 23, 63, 31,
38, 6, 46, 14, 54, 22, 62, 30,
37, 5, 45, 13, 53, 21, 61, 29,
36, 4, 44, 12, 52, 20, 60, 28,
35, 3, 43, 11, 51, 19, 59, 27,
34, 2, 42, 10, 50, 18, 58, 26,
33, 1, 41, 9, 49, 17, 57, 25
]
return bin2hex(permute(combined, final_permutation))
def des_decrypt(ciphertext, key):
round_keys = key_schedule(key)[::-1]
return des_encrypt(ciphertext, key)
# Example usage
key = "133457799BBCDFF1" # 64-bit key (16 hex digits)
plaintext = "0123456789ABCDEF" # 64-bit plaintext (16 hex digits)
ciphertext = des_encrypt(plaintext, key)
print("Ciphertext:", ciphertext)
decrypted_text = des_decrypt(ciphertext, key)
print("Decrypted Text:", decrypted_text)