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des.py
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def pad(block, p, bs):
return block + p * (bs - len(block))
def split(m, bs):
ret = []
for i in range(len(m) // bs):
ret.append(m[i*bs:(i+1)*bs])
if len(m) % bs != 0:
ret.append(pad(m[(len(m)//bs) * bs:], '0', bs)) # pad with 0
return ret
def PC1(k):
matrix = [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,
63, 55, 47, 39, 31, 23, 15,
7, 62, 54, 46, 38, 30, 22,
14, 6, 61, 53, 45, 37, 29,
21, 13, 5, 28, 20, 12, 4]
ret = list(len(matrix) * "0")
for i in range(len(matrix)):
ret[i] = k[matrix[i] - 1] # convert to 0-indexed
ret = ''.join(ret)
return ret
def PC2(k):
matrix = [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]
ret = list(len(matrix) * "0")
for i in range(len(matrix)):
ret[i] = k[matrix[i] - 1]
ret = ''.join(ret)
return ret
def shift_left(m, n_bits):
return m[n_bits:] + m[:n_bits]
def generate_subkeys(k):
ret = []
k = PC1(k) # 56-bit
c, d = k[:28], k[28:]
shift_table = [1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1]
for i in range(16):
c, d = shift_left(c, shift_table[i]), shift_left(d, shift_table[i])
ret.append(PC2(c + d))
return ret
def IP(m):
ret = list(len(m) * "0")
matrix = [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]
for i in range(len(m)):
ret[i] = m[matrix[i] - 1]
ret = ''.join(ret)
return ret
def E(m):
matrix = [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]
ret = list(len(matrix) * "0")
for i in range(len(matrix)):
ret[i] = m[matrix[i] - 1]
ret = ''.join(ret)
return ret
# a and b are strings of 0 and 1
def xor(a, b):
n = len(a)
c = ""
for i in range(n):
if ord(a[i]) ^ ord(b[i]) == 0:
c += '0'
else:
c += '1'
return c
def sbox(m, box):
row = int(m[0] + m[5], 2)
col = int(m[1:5], 2)
ret = bin(box[row * 16 + col])[2:]
ret = (4 - len(ret)) * "0" + ret
return ret
def SBOX(m):
# split into 6-bit blocks
blocks = split(m, 6)
ret = []
S1 = [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]
S2 = [15,1,8,14,6,11,3,4,9,7,2,13,12,0,5,10,
3,13,4,7,15,2,8,14,12,0,1,10,6,9,11,5,
0,14,7,11,10,4,13,1,5,8,12,6,9,3,2,15,
13,8,10,1,3,15,4,2,11,6,7,12,0,5,14,9]
S3 = [10,0,9,14,6,3,15,5,1,13,12,7,11,4,2,8,
13,7,0,9,3,4,6,10,2,8,5,14,12,11,15,1,
13,6,4,9,8,15,3,0,11,1,2,12,5,10,14,7,
1,10,13,0,6,9,8,7,4,15,14,3,11,5,2,12]
S4 = [7,13,14,3,0,6,9,10,1,2,8,5,11,12,4,15,
13,8,11,5,6,15,0,3,4,7,2,12,1,10,14,9,
10,6,9,0,12,11,7,13,15,1,3,14,5,2,8,4,
3,15,0,6,10,1,13,8,9,4,5,11,12,7,2,14]
S5 = [2,12,4,1,7,10,11,6,8,5,3,15,13,0,14,9,
14,11,2,12,4,7,13,1,5,0,15,10,3,9,8,6,
4,2,1,11,10,13,7,8,15,9,12,5,6,3,0,14,
11,8,12,7,1,14,2,13,6,15,0,9,10,4,5,3]
S6 = [12,1,10,15,9,2,6,8,0,13,3,4,14,7,5,11,
10,15,4,2,7,12,9,5,6,1,13,14,0,11,3,8,
9,14,15,5,2,8,12,3,7,0,4,10,1,13,11,6,
4,3,2,12,9,5,15,10,11,14,1,7,6,0,8,13]
S7 = [4,11,2,14,15,0,8,13,3,12,9,7,5,10,6,1,
13,0,11,7,4,9,1,10,14,3,5,12,2,15,8,6,
1,4,11,13,12,3,7,14,10,15,6,8,0,5,9,2,
6,11,13,8,1,4,10,7,9,5,0,15,14,2,3,12]
S8 = [13,2,8,4,6,15,11,1,10,9,3,14,5,0,12,7,
1,15,13,8,10,3,7,4,12,5,6,11,0,14,9,2,
7,11,4,1,9,12,14,2,0,6,10,13,15,3,5,8,
2,1,14,7,4,10,8,13,15,12,9,0,3,5,6,11]
ret.append(sbox(blocks[0], S1))
ret.append(sbox(blocks[1], S2))
ret.append(sbox(blocks[2], S3))
ret.append(sbox(blocks[3], S4))
ret.append(sbox(blocks[4], S5))
ret.append(sbox(blocks[5], S6))
ret.append(sbox(blocks[6], S7))
ret.append(sbox(blocks[7], S8))
return "".join(ret)
def P(m):
ret = list(len(m) * "0")
matrix = [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]
for i in range(len(m)):
ret[i] = m[matrix[i] - 1]
ret = ''.join(ret)
return ret
def IPinv(m):
ret = list(len(m) * "0")
matrix = [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]
for i in range(len(m)):
ret[i] = m[matrix[i] - 1]
ret = ''.join(ret)
return ret
if __name__ == "__main__":
message = input("Input message: ")
assert len(message) == 64
key = input("Input key: ")
assert len(key) == 64
decryption = input("Decryption? (y/n): ") == "y"
# generate 16 subkeys
subkeys = generate_subkeys(key)
if decryption:
subkeys = subkeys[::-1]
# initial permutation
message = IP(message)
print(f"IP(M) = {message}")
le, re = message[:32], message[32:]
for i in range(16):
round = i+1
expanded = E(re)
print(f"Round {round}")
print(f"SubKey {round} = {subkeys[i]}")
print(f"E(re) = {expanded}")
xored = xor(expanded, subkeys[i])
print(f"Xor(E(re), Ki) = {xored}")
sboxed = SBOX(xored)
print(f"SBOX(Xor(E(re), Ki)) = {sboxed}")
permuted = P(sboxed)
print(f"P(SBOX(Xor(E(re), Ki))) = {permuted}")
le, re = re, xor(le, permuted)
print(f"LE = {le}, RE = {re}")
print("=========================")
# swap (of Feistel)
le, re = re, le
# inverse initial permutation
ciphertext = IPinv(le + re)
print(f"IP-1({le + re}) = {ciphertext}")