替换密码 - 爱码网

替代密码是指先建立一个替换表，加密时将需要加密的明文依次通过查表，替换为相应的字符，明文字符被逐个替换后，生成无任何意义的字符串，即密文，替代密码的密钥就是其替换表。

分为单表替换与多表替换，此处讨论单表替换

加密解密实例：

 1 # Simple Substitution Cipher
 2 # http://inventwithpython.com/hacking (BSD Licensed)
 3 
 4 import pyperclip, sys, random
 5 
 6 
 7 LETTERS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
 8 
 9 def main():
10     myMessage = 'If a man is offered a fact which goes against his instincts, he will scrutinize it closely, and unless the evidence is overwhelming, he will refuse to believe it. If, on the other hand, he is offered something which affords a reason for acting in accordance to his instincts, he will accept it even on the slightest evidence. The origin of myths is explained in this way. -Bertrand Russell'
11     myKey = 'LFWOAYUISVKMNXPBDCRJTQEGHZ'
12     myMode = 'encrypt' # set to 'encrypt' or 'decrypt'
13 
14     checkValidKey(myKey)
15 
16     if myMode == 'encrypt':
17         translated = encryptMessage(myKey, myMessage)
18     elif myMode == 'decrypt':
19         translated = decryptMessage(myKey, myMessage)
20     print('Using key %s' % (myKey))
21     print('The %sed message is:' % (myMode))
22     print(translated)
23     pyperclip.copy(translated)
24     print()
25     print('This message has been copied to the clipboard.')
26 
27 
28 def checkValidKey(key):
29     keyList = list(key)
30     lettersList = list(LETTERS)
31     keyList.sort()
32     lettersList.sort()
33     if keyList != lettersList:
34         sys.exit('There is an error in the key or symbol set.')
35 
36 
37 def encryptMessage(key, message):
38     return translateMessage(key, message, 'encrypt')
39 
40 
41 def decryptMessage(key, message):
42     return translateMessage(key, message, 'decrypt')
43 
44 
45 def translateMessage(key, message, mode):
46     translated = ''
47     charsA = LETTERS
48     charsB = key
49     if mode == 'decrypt':
50         # For decrypting, we can use the same code as encrypting. We
51         # just need to swap where the key and LETTERS strings are used.
52         charsA, charsB = charsB, charsA
53 
54     # loop through each symbol in the message
55     for symbol in message:
56         if symbol.upper() in charsA:
57             # encrypt/decrypt the symbol
58             symIndex = charsA.find(symbol.upper())
59             if symbol.isupper():
60                 translated += charsB[symIndex].upper()
61             else:
62                 translated += charsB[symIndex].lower()
63         else:
64             # symbol is not in LETTERS, just add it
65             translated += symbol
66 
67     return translated
68 
69 
70 def getRandomKey():
71     key = list(LETTERS)
72     random.shuffle(key)
73     return ''.join(key)
74 
75 
76 if __name__ == '__main__':
77     main()

simpleSubCipher