源码来源：https://codereview.stackexchange.com/questions/108057/simplified-des-encryption
1. 源码修正后：
FIXED_IP
= [2, 6, 3, 1, 4, 8, 5, 7]
FIXED_EP
= [4, 1, 2, 3, 2, 3, 4, 1]
FIXED_IP_INVERSE
= [4, 1, 3, 5, 7, 2, 8, 6]
FIXED_P10
= [3, 5, 2, 7, 4, 10, 1, 9, 8, 6]
FIXED_P8
= [6, 3, 7, 4, 8, 5, 10, 9]
FIXED_P4
= [2, 4, 3, 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
= ''
def permutate(original
, fixed_key
):
new
= ''
for i
in fixed_key
:
new
+= original
[i
- 1]
return new
def left_half(bits
):
return bits
[:int(len(bits
)/2)]
def right_half(bits
):
return bits
[int(len(bits
)/2):]
def shift(bits
):
rotated_left_half
= left_half
(bits
)[1:] + left_half
(bits
)[0]
rotated_right_half
= right_half
(bits
)[1:] + right_half
(bits
)[0]
return rotated_left_half
+ rotated_right_half
def key1():
return permutate
(shift
(permutate
(KEY
, FIXED_P10
)), FIXED_P8
)
def key2():
return permutate
(shift
(shift
(shift
(permutate
(KEY
, FIXED_P10
)))), FIXED_P8
)
def xor(bits
, key
):
new
= ''
for bit
, key_bit
in zip(bits
, key
):
new
+= str(((int(bit
) + int(key_bit
)) % 2))
return new
def lookup_in_sbox(bits
, sbox
):
row
= int(bits
[0] + bits
[3], 2)
col
= int(bits
[1] + bits
[2], 2)
return '{0:02b}'.format(sbox
[row
][col
])
def f_k(bits
, key
):
L
= left_half
(bits
)
R
= right_half
(bits
)
bits
= permutate
(R
, FIXED_EP
)
bits
= xor
(bits
, key
)
bits
= lookup_in_sbox
(left_half
(bits
), S0
) + lookup_in_sbox
(right_half
(bits
), S1
)
bits
= permutate
(bits
, FIXED_P4
)
return xor
(bits
, L
)
def encrypt(plain_text
):
bits
= permutate
(plain_text
, FIXED_IP
)
temp
= f_k
(bits
, key1
())
bits
= right_half
(bits
) + temp
bits
= f_k
(bits
, key2
())
print('The encryption result is = ' + permutate
(bits
+ temp
, FIXED_IP_INVERSE
))
def decrypt(cipher_text
):
bits
= permutate
(cipher_text
, FIXED_IP
)
temp
= f_k
(bits
, key2
())
bits
= right_half
(bits
) + temp
bits
= f_k
(bits
, key1
())
print('The decryption result is = ' + permutate
(bits
+ temp
, FIXED_IP_INVERSE
))
if __name__
== '__main__':
oper
= input('Enter D for encryption and E for decryption：')
KEY
= input('Enter the 10-digit key：')
if oper
== 'D':
msg
= input('Enter 8-digit plaintext：')
encrypt
(msg
)
elif oper
== 'E':
msg
= input('Enter 8-digit ciphertext：')
decrypt
(msg
)
input('--- Type enter to end the process ---')
关于S-DES
什么是Simplified DES
