Chapter ? - Secret Code 2

secret2.py

1. # Secret Code 2 - Transpositional cipher
2. import cryptoLib
4. MAX_KEY_SIZE = 100
6. def main():
7.     mode = cryptoLib.getMode()
8.     message = cryptoLib.getMessage()
9.     key = cryptoLib.getKey(MAX_KEY_SIZE)
10.     
11.     print 'Your translated text is:'
12.     print getTranslatedMessage(mode, message, key)
14. def getTranslatedMessage(mode, message, key):
15.     if mode in 'encrypt e'.split():
16.         return encrypt(message, key)
17.     if mode in 'decrypt d'.split():
18.         return decrypt(message, key)
19.     
20. def encrypt(message, key):
21.     message += ' ' * (key - (len(message) % key))
22.     
23.     # Create a list of lists.
24.     table = []
25.     for i in range(key):
26.         table.append([])
27.     
28.     # Start encrypting the data.    
29.     column = 0
30.     for i in message:
31.         table[column].append(i)
32.         column += 1
33.         if column == key:
34.             column = 0
35.     
36.     # For debugging, display the table of columns:
37.     #for column in table:
38.     #    print column
39.     
40.     ciphertext = ''
41.     for i in table:
42.         ciphertext += ''.join(i)
43.         
44.     return ciphertext
45.     
46. def decrypt(message, key):
47.     # Decryption is the same as encryption, except with a different key.
48.     key = int( len(message) / key )
49.     
50.     if (len(message) - int(len(message)/key) * key) > 0:
51.         key += 1
53.     return encrypt(message, key)
54.         
55. if __name__ == '__main__':
56.     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: