#Cypher.py
#A program that encrypts/decrypts a message
 
import string
 
def main():
    print"This program will either encrypt or decrypt a message."
 
    mess = raw_input("Please enter your message: ")
    meth = raw_input("Enter 0 for encryption, 1 for decryption: ")
    while meth >= "2":
        print "Please enter 0 or 1 ONLY."
        meth = raw_input("Enter 0 for encryption, 1 for decryption: ")
    key = raw_input("What key index do you want to use: ")
 
    mesCode = []
 
    if meth == "0":
        for ch in(mess):
            ch = chr(ord(ch)+ eval(key))
            mesCode.append(ch)
    elif meth == "1":
        for ch in(mess):
            ch = chr(ord(ch) - eval(key))
            mesCode.append(ch)
 
 
    print string.join(mesCode,"")
 
main()

# example of simple encoding/decoding using Python's 'rot13'
# alphabet is shifted by 13 positions to nopqrstuvwxyzabcdefghijklm
# so original 'a' becomes 'n' or 'A' becomes 'N' and so on 
# (non-alpha characters are not affected)
 
text = "Peanuts88-q"
print "original =", text
 
encoded = text.encode('rot13')
print "encoded  =", encoded
 
decoded = encoded.encode('rot13')
print "decoded  =", decoded
 
"""
output -->
original = Peanuts88-q
encoded  = Crnahgf88-d
decoded  = Peanuts88-q
"""