Gavin writes:

> Wirt writes:
>  > For this kind of application, we can generate a encryption routine that
>  > will be essentially unbreakable, so long as we don't tell anyone what
>  > the algorithm is.
>
>  With all due respect, this is unlikely.  You can do something to
>  "obfuscate" the data stream so that it does not appear to be plain
>  text, but any "do it yourself" encryption algorithm is almost
>  always no better than a relatively simple obfuscation, no matter
>  how much clever code or mathematical churning you put in.  That is,
>  the cost to figure out a relatively simple obfuscation is probably
>  not much less than that to break a "high-powered" do-it-yourself
>  encryption algorithm.

With equal respect, let me disagree. All that you have to do to really make
something "obfuscated" is intermix a great deal of randomness into an
encrypted signal, paying special attention to make the random symbols carry
the same informational entropy as the encoded data.

The only way to break a code where you have no idea what algorithm has been
employed (or what the messages are) is to perform some sort of signal analysis
on a very large number of observations. The simple way to befuddle such an
analytical approach is to simply swamp the signal analyzer with meaningless
noise.

This is the idea behind those routines that want to impose mechanical chaos
into an encryption stream, as are currently popular at places like Los Alamos
and Lawrence Livermore. The encryption stream looks like noise. It tastes like
noise. But chaos isn't noise. It is predictable -- and is therefore lossless
in its informational recovery.

We don't need to go to the same level of trouble as Los Alamos. A little bit
of such encryption goes a long ways -- and any such encryption routine would
be far better than anything that was used during WWII (and most of that code
was never broken, other than by stealing the code books or capturing the
decryption machines).

And that still remains the simple method to break any routine: get hold of the
decrypting code, decompile it, understand the algorithm, and proceed from
there. Or just ask somebody for the key (they apparently willingly give it to
you surprisingly often).

Wirt Atmar