Python:實現S-DES加密算法
def apply_table(inp, table):
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: ")
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]]
# 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)
