Re: encrypted email software

[peter honeyman <honey@citi.umich.edu>]

> People first thought there was a back door because they wouldn't release 
> enough info on the algorithm to give people a chance to see if they 
> trusted it or not.

not the algorithm, which was public from the start, but the rationale behind
the selection of its parameters.

>                     After it was all common knowledge, people examined 
> it and came to the conclusion that it was secure, 

the rationale remains classified; some people question nsa's motivation
in keeping that aspect of des secret.  i believe nsa keeps it secret to
avoid teaching potential (or imaginary) adversaries advanced cryptographic
techniques.   (and also because keeping secrets is what nsa is all about.
they seem to be very, very good at it.)

>                                                   though questions are 
> still around about why it was changed from 64 bit to 56 bit,

you mean 112 -> 56.  this has been resolved -- it seems that longer keys
don't impose any additional complexity on des attacks.  although these
attacks were discovered by the open crypto community only a few years ago,
nsa had these techniques in hand long before.  the bottom line is that
additional key bits would not make des more secure.  double des or triple
des do.

>                                                              which is 
> also why it is believed that the NSA has computers that can break it by 
> brute force in a reasonable amount of time, but nevertheless it is a 
> brute force attack.

it has long been believed that a dedicated des-cracker is within the budget
of extremely well financed organizations.  

> That's how I've heard (from various sources) the whole story with DES 
> goes, and it seems like a reasonable one.

your story is pretty close to the spin i'm familiar with.

	peter