Re: Double Encryption Illegal?

Mok-Kong Shen wrote:
>
> Tom St Denis wrote:
> >
> > Mok-Kong Shen <mok-kong.shen_at_t-online.de> wrote:
> > >
> > >
> > > Tom St Denis wrote:
> > > >
> > > > pausch_at_saafNOSPAM.se (Paul Schlyter) wrote:
 

> > > > > So you're claiming that triple-DES is no more secure than single-
> > > > DES ???
> > > >
> > > > Read my message. Geez. I said "double" encryption is not the way
 to
> > > > go about added security.
> > >
> > > Could you be more explicit and explain why? Are you
> > > saying that superencipherment is always nonsense?
> > > Is 2-DES not better than DES?
> >
> > Given sufficient memory 2-des is not better then des.
>
> Please exlpain your claim or refer to literature.

That is the reason why people use 3DES, and never 2DES.

Well this has been explained, for example, in Bruce Schneiers Applied Crypto. At least I think so ;-), I don't have it at hand in the moment. There is an attack which requires masses of memory, but then you can attack 2DES by attacking it from both ends (meet-in-the-middle-attack).

It is also explained in my other crypto book, "Abendteuer Kryptologie" (Adventure Cryptology), by Reinhard Wobst, Addison Wesley, ISBN 3-8273-1413-5, page 192ff.

I think every not too short book which discusses DES would contain this proof. Received on Mon Sep 18 2000 - 13:53:44 CEST