Add the s-des library.

cryptography_s_des_exploring/sdes/sdes.py

@@ -0,0 +1,101 @@
+"""
+Reference: https://github.com/TheAlgorithms/Python/blob/master/other/sdes.py
+"""
+
+p8_table = [6, 3, 7, 4, 8, 5, 10, 9]
+p10_table = [3, 5, 2, 7, 4, 10, 1, 9, 8, 6]
+p4_table = [2, 4, 3, 1]
+IP = [2, 6, 3, 1, 4, 8, 5, 7]
+IP_inv = [4, 1, 3, 5, 7, 2, 8, 6]
+expansion = [4, 1, 2, 3, 2, 3, 4, 1]
+s0 = [[1, 0, 3, 2], [3, 2, 1, 0], [0, 2, 1, 3], [3, 1, 3, 2]]
+s1 = [[0, 1, 2, 3], [2, 0, 1, 3], [3, 0, 1, 0], [2, 1, 0, 3]]
+
+def apply_table(inp, table):
+    """
+    >>> apply_table("0123456789", list(range(10)))
+    '9012345678'
+    >>> apply_table("0123456789", list(range(9, -1, -1)))
+    '8765432109'
+    """
+    res = ""
+    for i in table:
+        res += inp[i - 1]
+    return res
+
+
+def left_shift(data):
+    """
+    >>> left_shift("0123456789")
+    '1234567890'
+    """
+    return data[1:] + data[0]
+
+
+def xor(a, b):
+    """
+    >>> xor("01010101", "00001111")
+    '01011010'
+    """
+    res = ""
+    for i in range(len(a)):
+        if a[i] == b[i]:
+            res += "0"
+        else:
+            res += "1"
+    return res
+
+
+def apply_sbox(s, data):
+    row = int("0b" + data[0] + data[-1], 2)
+    col = int("0b" + data[1:3], 2)
+    return bin(s[row][col])[2:]
+
+
+def function(expansion, s0, s1, key, message):
+    left = message[:4]
+    right = message[4:]
+    temp = apply_table(right, expansion)
+    temp = xor(temp, key)
+    l = apply_sbox(s0, temp[:4])  # noqa: E741
+    r = apply_sbox(s1, temp[4:])
+    l = "0" * (2 - len(l)) + l  # noqa: E741
+    r = "0" * (2 - len(r)) + r
+    temp = apply_table(l + r, p4_table)
+    temp = xor(left, temp)
+    return temp + right
+
+
+if __name__ == "__main__":
+    key = input("Enter 10 bit key: ")
+    message = input("Enter 8 bit message: ")
+
+    # key generation
+    temp = apply_table(key, p10_table)
+    left = temp[:5]
+    right = temp[5:]
+    left = left_shift(left)
+    right = left_shift(right)
+    key1 = apply_table(left + right, p8_table)
+    left = left_shift(left)
+    right = left_shift(right)
+    left = left_shift(left)
+    right = left_shift(right)
+    key2 = apply_table(left + right, p8_table)
+
+    # encryption
+    temp = apply_table(message, IP)
+    temp = function(expansion, s0, s1, key1, temp)
+    temp = temp[4:] + temp[:4]
+    temp = function(expansion, s0, s1, key2, temp)
+    CT = apply_table(temp, IP_inv)
+    print("Cipher text is:", CT)
+
+    # decryption
+    temp = apply_table(CT, IP)
+    temp = function(expansion, s0, s1, key2, temp)
+    temp = temp[4:] + temp[:4]
+    temp = function(expansion, s0, s1, key1, temp)
+    PT = apply_table(temp, IP_inv)
+    print("Plain text after decypting is:", PT)
+