Re: Simple cipher program help

From: ošin (ošin_at_ragnarok.com)
Date: 04/28/03 

Date: Mon, 28 Apr 2003 11:11:58 -0700

> I'm trying to write a program to take 64bits of plaintext in, using some
> kind of key, create 64bit cipher text.
>
> All this done over 16 iterations. Kind of like a really simple DES.
>
> I'm no good at programming, and just new to ciphertext - its just a little
> part of my school course.
>
> I was thinking, getting the input and key to binary, then XORing them,
then
> for each result, XORing it with the key.
>
> Will this work, or be reversible?

It will not work too well. You say that you XOR the input with the key to
get the first round result. Then you XOR that round result with the same key
to get the next round result. That means that on each even numbered round,
you XOR twice with the same key, which just gives you back the original
plaintext. After 16 rounds, you have not encrypted anything. Even if you did
toggle any bits, there is still the problem that you have not shuffled any
of the bits within the data. You should try to diffuse the data after each
round as well.

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