Simple way to encode a string according to a password?

Question

Does Python have a built-in, simple way of encoding/decoding strings using a password?

Something like this:

>>> encode('John Doe', password = 'mypass')
'sjkl28cn2sx0'
>>> decode('sjkl28cn2sx0', password = 'mypass')
'John Doe'

So the string "John Doe" gets encrypted as 'sjkl28cn2sx0'. To get the original string, I would "unlock" that string with the key 'mypass', which is a password in my source code. I'd like this to be the way I can encrypt/decrypt a Word document with a password.

I would like to use these encrypted strings as URL parameters. My goal is obfuscation, not strong security; nothing mission critical is being encoded. I realize I could use a database table to store keys and values, but am trying to be minimalist.

Answer 1

Assuming you are only looking for simple obfuscation that will obscure things from the very casual observer, and you aren't looking to use third party libraries. I'd recommend something like the Vigenere cipher. It is one of the strongest of the simple ancient ciphers.

Vigenère cipher

It's quick and easy to implement. Something like:

import base64

def encode(key, string):
    encoded_chars = []
    for i in xrange(len(string)):
        key_c = key[i % len(key)]
        encoded_c = chr(ord(string[i]) + ord(key_c) % 256)
        encoded_chars.append(encoded_c)
    encoded_string = "".join(encoded_chars)
    return base64.urlsafe_b64encode(encoded_string)

Decode is pretty much the same, except you subtract the key.

It is much harder to break if the strings you are encoding are short, and/or if it is hard to guess the length of the passphrase used.

If you are looking for something cryptographic, PyCrypto is probably your best bet, though previous answers overlook some details: ECB mode in PyCrypto requires your message to be a multiple of 16 characters in length. So, you must pad. Also, if you want to use them as URL parameters, use base64.urlsafe_b64_encode(), rather than the standard one. This replaces a few of the characters in the base64 alphabet with URL-safe characters (as it's name suggests).

However, you should be ABSOLUTELY certain that this very thin layer of obfuscation suffices for your needs before using this. The Wikipedia article I linked to provides detailed instructions for breaking the cipher, so anyone with a moderate amount of determination could easily break it.