lightweight encryption of text file

[Arnaud Delobelle]

Daniel Fetchinson <fetchinson at googlemail.com> writes:

> I have a plain text file which I would like to protect in a very
> simple minded, yet for my purposes sufficient, way. I'd like to
> encrypt/convert it into a binary file in such a way that possession of
> a password allows anyone to convert it back into the original text
> file while not possessing the password one would only see the
> following with the standard linux utility 'file':
>
> [fetchinson at fetch ~]$ file encrypted.data
> encrypted.data: data
[...]

This is probably not what you want, but it is very simple and doesn't
import any module:) I am not qualified to say how easy it is to discover
the message without the password.

def str2int(txt):
    return reduce(lambda n, c: n*255 + ord(c), txt, 0)

def int2str(n):
    chars = []
    while n:
        n, o = divmod(n, 255)
        chars.append(chr(o))
    return ''.join(reversed(chars))

def encrypt(txt, pwd):
    return int2str(str2int(txt)*str2int(pwd))

def decrypt(txt, pwd):
    return int2str(str2int(txt)/str2int(pwd))

def test(txt, pwd):
    encrypted_txt = encrypt(txt, pwd)
    decrypted_txt = decrypt(encrypted_txt, pwd)
    print "text:%r" % txt
    print "encrypted:%r" % encrypted_txt
    print "decrypted:%r" % decrypted_txt


>>> test("This encryption scheme is definitely unbreakable.", "secret")
text:'This encryption scheme is definitely unbreakable.'
encrypted:'&2\xa5\xd4\x17i+E\x01k\xfa\x94\xf80\xa8\x8f\xea.w\x128\xf1\xd9\x0f9\xf2t\xc9\r`\x90%\xd6\xf3~\x1f\x00%u&\x8a\xe4\xe0\xa7\xb8\xb0ec)S>\xcb\xf2>\xec'
decrypted:'This encryption scheme is definitely unbreakable.'

-- 
Arnaud