DES（Data Encryption Standard）是經典的對稱式區塊加密演算法，雖然目前已被 AES 取代，但在許多舊系統與教學場合仍廣泛使用。本文將完整呈現一個純 Python 實作的 DES 加密解密類別，包含金鑰排程、初始置換、Feistel 網路、S-box 替換等核心邏輯，並提供可直接執行的範例程式碼。
DES 類別封裝了完整的加密流程，主要介面包含三個方法：
input_key(key, base=10)：輸入金鑰，支援二進位、十六進位與字串三種格式encode(plaintext)：加密明文，自動補齊至 8 位元組倍數decode(ciphertext)：解密密文，移除填充並回傳 UTF-8 字串程式碼內建標準 DES 的初始置換表（__ip）、逆初始置換表（__ip1）、擴展置換表（__e）、P-box 置換表（__p）以及 8 個 S-box（__s），完全對應 FIPS 46-3 標準。
使用 __k1（PC-1）、__k2（PC-2）與 __k0（左移位數表）產生 16 個 48-bit 子金鑰，儲存於 self.__k 供加密/解密輪流使用。
__code 方法實作 16 輪 Feistel 結構：
#coding=utf-8
from functools import partial
import base64
class DES(object):
""" DES加密算法 interface: input_key(s, base=10), encode(s), decode(s) """
__ip = [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]
__ip1 = [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]
__e = [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]
__p = [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]
__s = [[0xe,0x4,0xd,0x1,0x2,0xf,0xb,0x8,0x3,0xa,0x6,0xc,0x5,0x9,0x0,0x7,
0x0,0xf,0x7,0x4,0xe,0x2,0xd,0x1,0xa,0x6,0xc,0xb,0x9,0x5,0x3,0x8,
0x4,0x1,0xe,0x8,0xd,0x6,0x2,0xb,0xf,0xc,0x9,0x7,0x3,0xa,0x5,0x0,
0xf,0xc,0x8,0x2,0x4,0x9,0x1,0x7,0x5,0xb,0x3,0xe,0xa,0x0,0x6,0xd],
[0xf,0x1,0x8,0xe,0x6,0xb,0x3,0x4,0x9,0x7,0x2,0xd,0xc,0x0,0x5,0xa,
0x3,0xd,0x4,0x7,0xf,0x2,0x8,0xe,0xc,0x0,0x1,0xa,0x6,0x9,0xb,0x5,
0x0,0xe,0x7,0xb,0xa,0x4,0xd,0x1,0x5,0x8,0xc,0x6,0x9,0x3,0x2,0xf,
0xd,0x8,0xa,0x1,0x3,0xf,0x4,0x2,0xb,0x6,0x7,0xc,0x0,0x5,0xe,0x9],
[0xa,0x0,0x9,0xe,0x6,0x3,0xf,0x5,0x1,0xd,0xc,0x7,0xb,0x4,0x2,0x8,
0xd,0x7,0x0,0x9,0x3,0x4,0x6,0xa,0x2,0x8,0x5,0xe,0xc,0xb,0xf,0x1,
0xd,0x6,0x4,0x9,0x8,0xf,0x3,0x0,0xb,0x1,0x2,0xc,0x5,0xa,0xe,0x7,
0x1,0xa,0xd,0x0,0x6,0x9,0x8,0x7,0x4,0xf,0xe,0x3,0xb,0x5,0x2,0xc],
[0x7,0xd,0xe,0x3,0x0,0x6,0x9,0xa,0x1,0x2,0x8,0x5,0xb,0xc,0x4,0xf,
0xd,0x8,0xb,0x5,0x6,0xf,0x0,0x3,0x4,0x7,0x2,0xc,0x1,0xa,0xe,0x9,
0xa,0x6,0x9,0x0,0xc,0xb,0x7,0xd,0xf,0x1,0x3,0xe,0x5,0x2,0x8,0x4,
0x3,0xf,0x0,0x6,0xa,0x1,0xd,0x8,0x9,0x4,0x5,0xb,0xc,0x7,0x2,0xe],
[0x2,0xc,0x4,0x1,0x7,0xa,0xb,0x6,0x8,0x5,0x3,0xf,0xd,0x0,0xe,0x9,
0xe,0xb,0x2,0xc,0x4,0x7,0xd,0x1,0x5,0x0,0xf,0xa,0x3,0x9,0x8,0x6,
0x4,0x2,0x1,0xb,0xa,0xd,0x7,0x8,0xf,0x9,0xc,0x5,0x6,0x3,0x0,0xe,
0xb,0x8,0xc,0x7,0x1,0xe,0x2,0xd,0x6,0xf,0x0,0x9,0xa,0x4,0x5,0x3],
[0xc,0x1,0xa,0xf,0x9,0x2,0x6,0x8,0x0,0xd,0x3,0x4,0xe,0x7,0x5,0xb,
0xa,0xf,0x4,0x2,0x7,0xc,0x9,0x5,0x6,0x1,0xd,0xe,0x0,0xb,0x3,0x8,
0x9,0xe,0xf,0x5,0x2,0x8,0xc,0x3,0x7,0x0,0x4,0xa,0x1,0xd,0xb,0x6,
0x4,0x3,0x2,0xc,0x9,0x5,0xf,0xa,0xb,0xe,0x1,0x7,0x6,0x0,0x8,0xd],
[0x4,0xb,0x2,0xe,0xf,0x0,0x8,0xd,0x3,0xc,0x9,0x7,0x5,0xa,0x6,0x1,
0xd,0x0,0xb,0x7,0x4,0x9,0x1,0xa,0xe,0x3,0x5,0xc,0x2,0xf,0x8,0x6,
0x1,0x4,0xb,0xd,0xc,0x3,0x7,0xe,0xa,0xf,0x6,0x8,0x0,0x5,0x9,0x2,
0x6,0xb,0xd,0x8,0x1,0x4,0xa,0x7,0x9,0x5,0x0,0xf,0xe,0x2,0x3,0xc],
[0xd,0x2,0x8,0x4,0x6,0xf,0xb,0x1,0xa,0x9,0x3,0xe,0x5,0x0,0xc,0x7,
0x1,0xf,0xd,0x8,0xa,0x3,0x7,0x4,0xc,0x5,0x6,0xb,0x0,0xe,0x9,0x2,
0x7,0xb,0x4,0x1,0x9,0xc,0xe,0x2,0x0,0x6,0xa,0xd,0xf,0x3,0x5,0x8,
0x2,0x1,0xe,0x7,0x4,0xa,0x8,0xd,0xf,0xc,0x9,0x0,0x3,0x5,0x6,0xb]]
__k1 = [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]
__k2 = [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]
__k0 = [1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1]
__hex_bin = {'0':'0000','1':'0001','2':'0010','3':'0011',
'4':'0100','5':'0101','6':'0110','7':'0111',
'8':'1000','9':'1001','a':'1010','b':'1011',
'c':'1100','d':'1101','e':'1110','f':'1111',' ':'0000'}
__re = lambda t, s: ''.join(s[i-1] for i in t)
__IP = partial(__re, __ip)
__IP1 = partial(__re, __ip1)
__E = partial(__re, __e)
__P = partial(__re, __p)
__K1 = partial(__re, __k1)
__K2 = partial(__re, __k2)
__B = partial(lambda hex_bin, s: ''.join(hex_bin[w] for w in ''.join('%2x' % ord(w) for w in s)), __hex_bin)
__DB = partial(lambda s: ''.join(chr(int(s[i:i+8], 2)) for i in range(0, len(s), 8)))
__S = partial(lambda hex_bin, __s, s: ''.join(hex_bin['%x' % __s[i][int(s[i*6]+s[i*6+5], 2)*16 + int(s[i*6+1:i*6+5], 2)]] for i in range(8)), __hex_bin, __s)
__F = partial(lambda s, k: ''.join('0' if s[i]==k[i] else '1' for i in range(len(s))))
__K0 = partial(lambda k0, K2, k: map(K2, (k[k0[i]:28]+k[0:k0[i]] + k[k0[i]+28:56]+k[28:k0[i]+28] for i in range(16))), __k0, __K2)
__K = partial(lambda K1, K0, k: K0(K1(k)), __K1, __K0)
def __init__(self):
pass
def input_key(self, key, base=10):
if base == 2:
pass
elif base == 16:
key = ''.join(self.__class__.__hex_bin[w] for w in key)
else:
key = self.__class__.__B(key)
self.__k = self.__class__.__K(key)
def __code(self, s, k):
s = self.__IP(s)
l, r = s[0:32], s[32:64]
for i in range(16):
r_t = r
r = self.__E(r)
r = self.__F(r, k[i])
r = self.__S(r)
r = self.__P(r)
r = self.__F(r, l)
l = r_t
return self.__class__.__IP1(r+l)
def encode(self, s):
a = ''
s += ' ' * ((8-len(s)%8)%8)
for i in range(0, len(s), 8):
before = self.__class__.__B(s[i:i+8])
after = self.__code(before, self.__k)
a += '%16x' % int(after, 2)
return ''.join(w if w!=' ' else '0' for w in a)
def decode(self, s):
a = ''
s = s.lower()
for i in range(0, len(s), 16):
before = ''.join(self.__class__.__hex_bin[s[j]] for j in range(i, i+16))
after = self.__code(before, self.__k[::-1])
a += self.__class__.__DB(after)
return a.rstrip().decode('utf-8')
if __name__ == '__main__':
d = DES()
d.input_key('123456789')
s = '再來一段中文'
a = d.encode(s)
print(a)
b = d.decode(a)
print(b)
>> d = DES()
>>> d.input_key('123456789')
>>> s = '再來一段中文'
>>> a = d.encode(s)
>>> print(a)
0000000000000000... (16進位密文)
>>> b = d.decode(a)
>>> print(b)
再來一段中文
⚠️ 注意：DES 僅使用 56-bit 有效金鑰，現代運算能力可在數小時內暴力破解。實務應用請改用 AES-256 或 ChaCha20-Poly1305 等現代加密演算法。本範例僅供教學與舊系統維護參考。
