🚀 go-pugleaf

shulick@indiana.edu (Sam Hulick) writes:
>
>NOTE: Yes, you may have noticed I'm posting a lot about breaking DES/UNIX
>encryption.  I am not a hacker, I'm merely trying to understand the way it
>works and learn exactly how secure this algorithm really is.  I gave up hacking
>a long time ago. (:
>
>Let's say someone retreives the DES source code, which is easy enough.  Why
>WOULDN'T they be able to take every single mathematical operation, reverse each
>one, and then have a "decrypt()"?  I know it's not that simple, but how has DES
>made it so even a good mathematician can't just reverse all the operations?
>

Obviously, if you know the key used, then DES is reversible - how else, can
the plaintext be retrieved.  However, if you mean is it possible to reverse 
the process to produce the plaintext & key from the ciphertext, then the answer
is NO.

Why not?  Each of the subkeys is used in an XOR operation, you can't reverse
this one to one.  A XOR B = C, if you know C you can't be sure what A and B are.

OK?

-- 
"Therefore was the name of it called Babel;  because Jehovah
 did there confound the language of all the earth." -Genesis 11:9
.
  John L.S.Davies          dc91jld@brunel.ac.uk
.
.