Chapter ? - Secret Code 1

secret1.py

1. # Secret Code 1 - Simple Substitution Cipher
3. MAX_KEY_SIZE = 26
5. def main():
6.     mode = getMode()
7.     message = getMessage()
8.     key = getKey()
9.     
10.     print 'Your translated text is:'
11.     print getTranslatedMessage(mode, message, key)
12.     
13. def getMode():
14.     mode = ''
15.     while (mode not in 'encrypt e decrypt d'.split()):
16.         print 'Do you wish to encrypt or decrypt a message?'
17.         mode = raw_input()
18.         mode = mode.lower()
20.         if (mode not in 'encrypt e decrypt d'.split()):
21.             print 'Enter either "encrypt" or "e" or "decrypt" or "d".'
22.     return mode
24. def getMessage():
25.     print 'Enter your message:'
26.     message = raw_input()
27.     
28.     return message
30. def getKey():
31.     key = 0
32.     while (not (key >= 1 and key <= MAX_KEY_SIZE)):
33.         print 'Enter the key number (1-%s)' % (MAX_KEY_SIZE)
34.         key = int(raw_input())
35.     return key
37. def getTranslatedMessage(mode, message, key):
38.     if mode in 'encrypt e'.split():
39.         return encrypt(message, key)
40.     if mode in 'decrypt d'.split():
41.         return decrypt(message, key)
43. def encrypt(message, key):
44.     cipherText = ''
45.     
46.     for symbol in message:
47.         if symbol.isalpha():
48.             num = ord(symbol)
49.     
50.             if symbol.isupper():
51.                 num -= ord('A')
52.             elif symbol.islower():
53.                 num -= ord('a')
54.     
55.             num += key
56.             num = num % 26
57.     
58.             if symbol.isupper():
59.                 num += ord('A')
60.             elif symbol.islower():
61.                 num += ord('a')
62.     
63.             cipherText += chr(num)
64.         else:
65.             cipherText += symbol
66.     return cipherText
68. def decrypt(message, key):
69.     plainText = ''
70.     
71.     for symbol in message:
72.         if symbol.isalpha():
73.             num = ord(symbol)
74.     
75.             if symbol.isupper():
76.                 num -= ord('A')
77.             elif symbol.islower():
78.                 num -= ord('a')
79.     
80.             num -= key
81.             num = num % 26
82.     
83.             if symbol.isupper():
84.                 num += ord('A')
85.             elif symbol.islower():
86.                 num += ord('a')
87.     
88.             plainText += chr(num)
89.         else:
90.             plainText += symbol
91.     return plainText
93. if __name__ == '__main__':
94.     main()

Things Covered In This Chapter: