[Tutor] How do I save the output of the rotor module?

[Danny Yoo]

On Thu, 6 Nov 2003, Mike Faire wrote:

> I wrote a simple script to get acquainted with the rotor module.
> Encrypting and decrypting was simple enough. However, once I save the
> encrypted list to a file, it will not decrypt correctly beyond the first
> newline.


Hi Mike,


'rotor' provides no guarantee that

    r.encrypt(a + b)

is the same as

    r.encrypt(a) + r.encrypt(b)



Let me check something...

###
>>> r = rotor.newrotor("606")
>>> r.encrypt("hello") + r.encrypt("world")
'~\xe5k\t&\n\x17@\t\x08'
>>>
>>>
>>> r = rotor.newrotor("606")
>>> r.encrypt("helloworld")
'~\xe5k\t&\x85\xe0>^\\'
###


So that's one issue we need to be aware of.



Another is that newlines themselves will be encoded!

###
>>> r.encrypt("\n\n\n")
'*\x86O'
###



These two facts interact in a funny way: since you're doing the encoding,
line by line:

> rt = rotor.newrotor('606')
> for item in contents:
>      encon.append(rt.encrypt(item))
> print encon

is very likely that the encoded file won't have the same number of
newlines as the original input.


This, combined with the knowledge that:

    r.encrypt(a) + r.encrypt(b) != r.encrypt(a + b)

should be enough to see that we're in trouble as soon as we try decoding
the string.  *grin*



Does this make sense so far?