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13-simpleSubCipher.py
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13-simpleSubCipher.py
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import sys, random
LETTERS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
def main():
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'
myKey = 'LFWOAYUISVKMNXPBDCRJTQEGHZ'
myMode = 'encrypt' # Set to either 'encrypt' or 'decrypt'.
#myMessage = raw_input('\nEnter message: ')
#myKey = raw_input("Encryption/decryption key: ")
#myKey = getRandomKey()
#myMode = raw_input("Would you like to \"encrypt\" or \"decrypt\" this message? ")
if not keyIsValid(myKey):
sys.exit('There is an error in the key or symbol set.')
if myMode == 'encrypt':
translated = encryptMessage(myKey, myMessage)
elif myMode == 'decrypt':
translated = decryptMessage(myKey, myMessage)
print '\nUsing key %s' % (myKey)
print '\nThe %sed message is:' % (myMode)
print '------------------------------------------------------------'
print translated
print '\n'
def keyIsValid(key):
keyList = list(key)
lettersList = list(LETTERS)
keyList.sort()
lettersList.sort()
return keyList == lettersList
def encryptMessage(key, message):
return translateMessage(key, message, 'encrypt')
def decryptMessage(key, message):
return translateMessage(key, message, 'decrypt')
def translateMessage(key, message, mode):
translated = ''
charsA = LETTERS
charsB = key
if mode == 'decrypt':
# For decrypting, we can use the same code as encrypting. We
# just need to swap where the key and LETTERS strings are used.
charsA, charsB = charsB, charsA
# Loop through each symbol in message:
for symbol in message:
if symbol.upper() in charsA:
# Encrypt/decrypt the symbol:
symIndex = charsA.find(symbol.upper())
if symbol.isupper():
translated += charsB[symIndex].upper()
else:
translated += charsB[symIndex].lower()
else:
# Symbol is not in LETTERS; just add it
translated += symbol
return translated
def getRandomKey():
key = list(LETTERS)
random.shuffle(key)
return ''.join(key)
if __name__ == '__main__':
main()