Cryptography Reference
In-Depth Information
Another approach is based on computer algebra. Modern computers can process
formulas. Though they don't handle them as elegantly as we humans do, they
faultlessly master 'tapeworms' millions of members long. Computers can even
work with algebraic structures, since operations in such structures meet exactly
defined laws. As the Enigma drums and their movements were fixed, the struc-
ture of the substitutions was well known. We could try to describe the depen-
dence of the substitutions in consecutive steps with appropriate expressions,
and then build a totally different cryptanalysis on that. The only question is
then whether or not it would still be worth our while.
One interesting initiative is the 'M4 Project'. (see
m4 project.txt
on the Web site
to this topic). The challenge is to break three original Enigma messages from
World War II that have not yet been deciphered by means of free software. This
so-called
hill-climbing method
is a mixture of experimenting with the rotor set-
tings and subsequently 'adapting' the plugboard. At the time of writing, one of
the messages has been decrypted. The project shows that Enigma cryptanalysis
is still no kid's game today.
Clipped, But Still Secret: UNIX-
crypt
The UNIX world has always had a command called
crypt
, which can be used
to encrypt files. This command runs a kind of Enigma with only one rotor and
one reflector (reversing drum). However, the rotor has 256 'contacts', because
it's a matter of encrypting bytes and not just letters. The method is insecure,
which mightn't come as a surprise after all you've read so far. Things looked
different when UNIX emerged in 1970.
To prove the insecurity claimed, Robert Baldwin of the MIT created a program
package called
Crypt Breakers Workbench
(
CBW
) in the mid-1980s. The prod-
uct offers a convenient interface for unauthorized deciphering of files encrypted
with
crypt
. The program is freely available; everybody can have a look at it
and analyze its functionality. Of course, it is also included on the Web site
to this topic. The Workbench integrates a program functionally equivalent to
crypt
(by the misleading name of
enigma.c
). Nevertheless,
crypt
is available
under UNIX for compatibility reasons. There's nothing unusual about it.
But now hold tight: until well into the 1990s, it was strictly forbidden to
export a UNIX system from the USA if it included
crypt. crypt
was considered
ammunition — you'll probably remember that part from Chapter 1.
crypt
was
stripped off every legally exported UNIX. On the UNIX systems SunOS 4.1.3
and on my ESIX V.4.2 (shipped at the end of 1994) I found
crypt
documented,
but
crypt
itself was missing. OSF/1 no longer offered
crypt
. Though I found
