Chapter ? - Secret Code 3

secret3.py

1. # Secret Code 3 - Vigenere Cipher
3. import cryptoLib
5. MAX_KEY_SIZE = 100
7. def main():
8.     mode = cryptoLib.getMode()
9.     message = cryptoLib.getMessage()
10.     key = getKeyWord()
11.     
12.     print 'Your translated text is:'
13.     print getTranslatedMessage(mode, message, key)
15. def getKeyWord():
16.     keyWord = ''
17.     print 'Enter the key word:'
18.     while keyWord.isalpha():
19.         keyWord = raw_input()
20.     return keyWord
22. def getTranslatedMessage(mode, message, key):
23.     if mode in 'encrypt e'.split():
24.         return encrypt(message, key)
25.     if mode in 'decrypt d'.split():
26.         return decrypt(message, key)
27.     
28. def encrypt(message, key):
29.     cipherText = ''
30.     keyPosition = 0
31.     
32.     for symbol in message:
33.         if symbol.isalpha():
34.             num = ord(symbol)
35.     
36.             if symbol.isupper():
37.                 num -= ord('A')
38.             elif symbol.islower():
39.                 num -= ord('a')
40.     
41.             num += ord(key[keyPosition])
42.             num = num % 26
43.             
44.             keyPosition += 1
45.             if keyPosition == len(key):
46.                 keyPosition = 0
47.     
48.             if symbol.isupper():
49.                 num += ord('A')
50.             elif symbol.islower():
51.                 num += ord('a')
52.     
53.             cipherText += chr(num)
54.         else:
55.             cipherText += symbol
56.     return cipherText
58. def decrypt(message, key):
59.     plainText = ''
60.     keyPosition = 0
61.     
62.     for symbol in message:
63.         if symbol.isalpha():
64.             num = ord(symbol)
65.     
66.             if symbol.isupper():
67.                 num -= ord('A')
68.             elif symbol.islower():
69.                 num -= ord('a')
70.     
71.             num -= ord(key[keyPosition])
72.             num = num % 26
73.             keyPosition += 1
74.             if keyPosition == len(key):
75.                 keyPosition = 0
76.     
77.             if symbol.isupper():
78.                 num += ord('A')
79.             elif symbol.islower():
80.                 num += ord('a')
81.     
82.             plainText += chr(num)
83.         else:
84.             plainText += symbol
85.     return plainText
87. if __name__ == '__main__':
88.     main()

cryptoLib.py

1. def getMode():
2.     mode = ''
3.     while (mode not in 'encrypt e decrypt d'.split()):
4.         print 'Do you wish to encrypt or decrypt a message?'
5.         mode = raw_input()
6.         mode = mode.lower()
8.         if (mode not in 'encrypt e decrypt d'.split()):
9.             print 'Enter either "encrypt" or "e" or "decrypt" or "d".'
10.     return mode
12. def getMessage():
13.     print 'Enter your message:'
14.     message = raw_input()
15.     
16.     return message
18. def getKey(maxKeySize):
19.     key = 0
20.     while (not (key >= 1 and key <= maxKeySize)):
21.         print 'Enter the key number (1-%s)' % (maxKeySize)
22.         key = int(raw_input())
23.     return key

Things Covered In This Chapter: