Python DES加密实现原理及实例解析

#################################辅助函数######################################
# 十进制转成二进制
def INT_BIN(NUM):
i = bin(NUM)[2:]
if len(i) != 8:
i = ((8 - len(i)) * '0') + i
return i
# 置换函数
def Replace(ARR,change):
ARR1 = []
for i in ARR:
a = ''
for j in change:
a += i[j-1]
ARR1.append(a)
return ARR1
# 异或运算
def XOR(a,b):
c=""
for i,j in zip(a,b):
if i==j:
c+='0'
else:
c+='1'
return [c]
# 二进制转字符
def ASCII(A):
text = ''
for i in A:
for j in range(8):
b = i[j*8:(j+1)*8]
text += chr(int(b,2))
return text
##############################################################################
#################################密钥生成######################################
# 先PC1置换、将56位密钥对半分L0和R0、分别对L0和R0进行左循环移位，
# （当轮数为第1、2、9、16轮时，移动1位，其余时候移动两位）L0,R0移动1位
# 后得到L1，R1，L1+R0进行PC2置换得到密钥K1，L1和R0继续进行下一轮，直到生成16个子密钥
# PC-1置换表
PC1 = [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]
# PC-2置换表
PC2 = [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]
# 生成子密钥函数
def GenerateSubkey(Key):
# 字符串转二进制
K = ""
i_byte = bytes(Key, encoding='utf-8')
for i_bin in i_byte:
K += INT_BIN(i_bin)
# PC1置换
ReplacePc1 = Replace([K],PC1)
# 生成16组子密钥
Lmi = []
Rmi = []
Lmi.append(ReplacePc1[0][:28])
Rmi.append(ReplacePc1[0][28:])
for i in range(1,17):
if i in (1, 2, 9, 16):
Lmi.append(Lmi[i-1][1:]+Lmi[i-1][:1])
Rmi.append(Rmi[i-1][1:]+Rmi[i-1][:1])
else:
Lmi.append(Lmi[i-1][2:]+Lmi[i-1][:2])
Rmi.append(Rmi[i-1][2:]+Rmi[i-1][:2])
del Lmi[0]
del Rmi[0]
del ReplacePc1[0]
for i in range(16):
ReplacePc1.append(Lmi[i]+Rmi[i])
# PC2置换
return Replace(ReplacePc1,PC2)
###########################################################################
#################################明文处理###################################
# 明文填充，采用PKCS #5规则，如果刚好满足每组有8个字节，则再添加一组，每个字节为
# 000010000，如果最后一组没有8个字节，则把这一组填充成8个字节，填充的字节为少掉的
# 字节的数目，比如有7个字节，则填充00000001
# 对明文进行填充，分组
def InitPlaintext(Plaintext):
DecimalList = []
BytesList = []
BinList = []
# 字符串转成10机制
i_byte = bytes(Plaintext, encoding='utf-8')
for i_bin in i_byte:
DecimalList.append(i_bin)
# 刚好满足分组
if len(DecimalList) % 8 == 0:
for i in range(8):
DecimalList.append(8)
for i in range(int(len(DecimalList)/8)):
BytesList.append(DecimalList[i*8:(i+1)*8])
# 不满足分组
else:
INT = 8 - len(DecimalList) % 8
for i in range(INT):
DecimalList.append(INT)
for i in range(int(len(DecimalList)/8)):
BytesList.append(DecimalList[i*8:(i+1)*8])
# 10进制转2进制
for i in BytesList:
TMP = ''
for j in i:
TMP += INT_BIN(j)
BinList.append(TMP)
return BinList
###########################################################################
################################feistel函数################################
#ip初始置换表
IPINIT = [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]
#扩展E置换表
EExten = [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盒置换表
PBOX = [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]
#逆初始置换表
P1 = [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]
#8个s盒
S_1 = [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]
S_2 = [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]
S_3 = [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]
S_4 = [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]
S_5 = [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]
S_6 = [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]
S_7 = [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]
S_8 = [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]
S_9 = []
S_9.append(S_1)
S_9.append(S_2)
S_9.append(S_3)
S_9.append(S_4)
S_9.append(S_5)
S_9.append(S_6)
S_9.append(S_7)
S_9.append(S_8)
# S盒置换
def S(R):
s = ''
for i in range(8):
a = R[i*6:(i+1)*6]
x = int(a[0]+a[-1],2)
y = int(a[1:5],2)
s += INT_BIN(S_9[i][x*15+y])[4:]
return[s]
# feistel函数
def feistel(L, R, K):
# 扩展置换
Expand = Replace(R,EExten)
# 异或运算
Expand = XOR(Expand[0],K)
# S盒运算
Expand = S(Expand[0])
# P盒
Expand = Replace(Expand,PBOX)
# 异或运算
Expand = XOR(L[0],Expand[0])
return Expand[0]
###########################################################################
################################加、解密函数################################
# 加密
def Encrypt(PlanText,Key):
# 初始置换
IP1 = Replace(InitPlaintext(PlanText),IPINIT)
# 生成子密钥
SubkeyList = GenerateSubkey(Key)
# 16轮迭代
Ciphertext = []
for i in IP1:
L = i[:32]
R = i[32:]
for k in SubkeyList:
TMP = feistel([L],[R],k)
L = R
R = TMP
# 逆初始置换
Ciphertext.append(Replace([R+L],P1)[0])
return Ciphertext,SubkeyList
# 解密
def Decrypt(Ciphertext,Key):
# 初始置换
IP1 = Replace(Ciphertext,IPINIT) 
# 16轮迭代
PlanText = []
for i in IP1:
L = i[:32]
R = i[32:]
for k in Key[::-1]:
TMP = feistel([L],[R],k)
L = R
R = TMP
# 逆初始置换
PlanText.append(Replace([R+L],P1)[0])
return PlanText
###########################################################################
if __name__ == "__main__":
miwen,miyao = Encrypt('computer','networks')
print(miwen)
print(ASCII(Decrypt(miwen,miyao)))