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# Caesar Cipher
# http://inventwithpython.com/codebreaker (BSD Licensed)
# the string to be encrypted/decrypted
message = 'This is my secret message.'
# the encryption/decryption key
key = 13
# tells the program to encrypt of decrypt
mode = 'encrypt' # set to 'encrypt' or 'decrypt'
# every possible symbol that can be encrypted
LETTERS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
# stores the encrypted/decrypted form of the message
translated = ''
# capitalize the string in message
message = message.upper()
# run the encryption/decryption code on each symbol in the message string
for symbol in message:
if symbol in LETTERS:
# get the encrypted (or decrypted) number for this symbol
num = LETTERS.find(symbol) # get the number of the symbol
if mode == 'encrypt':
num = num + key
elif mode == 'decrypt':
num = num - key
# handle the wrap around if num is larger than the length of LETTERS
# or less than 0
if num >= len(LETTERS):
num = num - len(LETTERS)
elif num < 0:
num = num + len(LETTERS)
# add encrypted/decrypted number's symbol at the end of translated
translated = translated + LETTERS[num]
else:
# just add the symbol without encrypting/decrypting
translated = translated + symbol
# print the encrypted/decrypted string to the screen
print(translated)
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