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DES.py
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# -*- coding: utf-8 -*-
# AUTHOR: Soreat_u (2019-05-14)
'''
DES (Data Encryption Standard) implementation.
'''
from Utility import Block2Bytes, BlockXor, Bytes2Block, Permute
'''Permutation Table'''
IP_table = [
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
] # ok
FP_table = [
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
] # ok
Expansion_table = [
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
] # ok
Permutation_table = [
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
] # ok
# There used to be a left PC-1 table and a right one,
# here I merge them into one table
PC_1_table = [
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
] # ok
PC_2_table = [
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
] # ok
sbox = [
[
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
],
[
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
],
[
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
],
[
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
],
[
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
],
[
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
],
[
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
],
[
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
]
] # ok
'''Process Function'''
# IP and FP are inverses(IP "undoes" the action of FP, and vice versa)
def IP(block):
'''
Initial permutation
'''
return Permute(block, IP_table) # ok
def FP(block):
'''
Final permutation
'''
return Permute(block, FP_table) # ok
# Feistel function
def Feistel(HalfBlock, subkey):
'''
The F-function, operating on half a block (32 bits) at a time and consisting of four stages:
1. Expansion, 2. Key mixing, 3. Substitution, 4. Permutation
'''
eHalfBlock = Expansion(HalfBlock)
xHalfBlock = BlockXor(eHalfBlock, subkey)
sHalfBlock = Substitution(xHalfBlock)
return Permutation(sHalfBlock) # ok
def Expansion(HalfBlock):
'''
Expand 32-bit half-block to 48 bits using the expansion permutation.
32-bit -> 48-bit
'''
return Permute(HalfBlock, Expansion_table) # ok
def Substitution(HalfBlock):
'''
Divide the block into eight 6-bit pieces and then use S-boxes(substitution boxes) to process the eight pieces.
After processing, the block is reduced from 48 bits to 32 bits.
48-bit -> 32-bit
'''
result = []
for i in range(8):
result += S_box(HalfBlock[6*i:6*i+6], i)
return result
def S_box(piece, i):
'''
Replace the six input bits with four output bits according to a non-linear transformation, provided in the form of a loopup table.
S-boxes provide the core of the security of DES, without which the cipher would be linear and easily broken.
6-bit -> 4-bit
'''
row = (piece[0] << 1) + piece[-1]
col = (piece[1] << 3) + (piece[2] << 2) + (piece[3] << 1) + piece[4]
s = sbox[i][16 * row + col]
result = []
for j in range(4):
result.append((s >> (3 - j)) & 1)
return result # ok
def Permutation(HalfBlock):
'''
Rearrange the 32 outputs from the S-boxes according to a fixed permutation
'''
return Permute(HalfBlock, Permutation_table) # ok
'''Encryption & Decryption'''
# Decryption uses the same structure as encryption, but merely with the keys used in reverse order.
def DES_enc(m, subkey):
'''
Encryption of DES.
:param bytes m: The message to be encrypted.
:param list key: The subkey to encrypt the message.
:return: The cipher after encryprtion.
:rtype: bytes
:raises TypeError: if the type of m is not `bytes`.
:raises ValueError: if message is not 8-byte in length.
'''
if type(m) != bytes:
raise TypeError("message must be type `bytes`")
elif len(m) != 8:
raise ValueError("message must be 64-bit in length")
# convert `bytes` m to block
m = Bytes2Block(m)
# Initial permutation
m = IP(m)
# divide the block into two 32-bit halves
Li, Ri = m[:32], m[32:]
# 16 rounds
for i in range(16):
Li, Ri = Ri, BlockXor(Li, Feistel(Ri, subkey[i]))
# merge the two divided half block which is 32-bit into one 64-bit block
m = Ri + Li # There is a need to change order of the final two halves
# Final permutation
m = FP(m)
# convert `block` m to `bytes`
return Block2Bytes(m) # ok
def DES_dec(c, subkey):
'''
Decryption of DES.
:param bytes c: The cipher to be decrypted
:param list subkey: The subkey to decrypt the cipher
:return: the message after decryption
:rtype: bytes
:raises TypeError: if the type of c is not `bytes`
:raises ValueError: if cipher is not 8-byte in length
'''
# Since decryption shares a lot similarity with encryption and the very difference between them\
# is the subkey (reversed), decryption is actually another form of encryption.
return DES_enc(c, subkey[::-1]) # ok
'''Key schedule'''
def gen_key(key):
'''
Generate the sixteen subkeys according to the key.
:param bytes key: The key to generate sixteen subkeys
:return: lists of the sixteen subkeys
:rtype: list
:raises TypeError: if the type of key is not `bytes`
:raises ValueError: if @key is not 56-bit or 64-bit in length
'''
# convert string key to bytes key
if type(key) != bytes:
raise TypeError("key must be type `bytes`")
bkey = Bytes2Block(key)
subkey = []
if len(bkey) == 64:
# PC-1
bkey = PC_1(bkey)
elif len(bkey) != 56:
raise ValueError("key must be 56-bit or 64-bit in length")
# divide the block into two halves
Ci, Di = bkey[:28], bkey[28:]
for i in range(16):
# Left Rotation
Ci, Di = LR(Ci, Di, i)
# PC-2
subkey.append(PC_2(Ci + Di))
return subkey # ok
def PC_1(key):
'''
Permutation Choice 1
Discard the parity check bits, which cuts the 64-bit key into 56-bit key and then permute.
64-bit -> 56-bit
'''
return(Permute(key, PC_1_table)) # ok
def LR(Ci, Di, i):
'''
Left Rotate the halfblock according to i.
'''
# 1 position shift if i = 1, 2, 9, 16 while 2 position shift all other i
keyoff = [1, 2, 9, 16]
if i + 1 in keyoff:
Ci, Di = Ci[1:] + Ci[0:1], Di[1:] + Di[0:1]
else:
Ci, Di = Ci[2:] + Ci[0:2], Di[2:] + Di[0:2]
return Ci, Di # ok
def PC_2(CiDi):
'''
Permutation Choice 2.
Drop 8 bits and permute the remaining 48 input bits.
56-bit -> 48-bit
'''
return(Permute(CiDi, PC_2_table)) # ok
'''Test'''
def test():
m = b"desisbad"
key = b"Imnotkey"
subkey = gen_key(key)
cipher = DES_enc(m, subkey)
message = DES_dec(cipher, subkey)
print(b"Message: " + message)
print(b"Key: " + key)
print(b"Cipher: " + cipher)
if __name__ == "__main__":
test()
# output:
# b'Message: desisbad'
# b'Key: Imnotkey'
# b'Cipher: \x0e2#b\xf9\xd4\xe5\x05'