From: Mike Johnson second login <exabyte!gedora!mikej2@uunet.uu.net>
Date: Fri, 15 Jul 94 14:45:58 PDT
To: Carl Ellison <gedora!uunet!tis.com!cme@uunet.uu.net>
Subject: Re: Triple encryption...
In-Reply-To: <9407151730.AA19916@tis.com>
Message-ID: <Pine.3.89.9407151559.A29784-0100000@gedora>
MIME-Version: 1.0
Content-Type: text/plain


> ...
> >> have you considered
> >>
> >>        des | tran | des | tran | des ?
> >
> >That one's sort of your "trademark", isn't it? <g> 
> 
> yup :-)
> 
> >clever, BTW.)  One scheme that seems to make even more sense, though, is:
> >
> >         des | tran | IDEA | tran | des
> >
> >You get the benefits of 112 bits worth of DES keyspace along with 128 bits
> >of IDEA keyspace, and thus don't stake your total security on the strength
> >of EITHER algorithm.
> 
> good, too.  Of course, it leaves open the question of which should be
> inside and which outside.
> ... 
> Yes, it's in response to Eli's paper that I advocated prngxor, as in:
> 
> 
>          des | prngxor | tran | des | tran | des
> 
> with the DES instances in ECB mode (in acknowledgement of Eli's attack).
> The prngxor destroys any patterns from the input, which was the purpose of
> CBC, without using the feedback path which Eli exploited.

Or for the rabid, clinically paranoid:

3des | tran | IDEA | tran | Diamond | tran | Blowfish | prngxor | 
3des | tran | IDEA | tran | Diamond | tran | Blowfish | prngxor | 
3des | tran | IDEA | tran | Diamond | tran | Blowfish | prngxor | 
3des | tran | IDEA | tran | Diamond | tran | Blowfish | prngxor | 
3des | tran | IDEA | tran | Diamond | tran | Blowfish | prngxor | 
3des | tran | IDEA | tran | Diamond | tran | Blowfish | prngxor | 
3des | tran | IDEA | tran | Diamond | tran | Blowfish | prngxor | 
3des | tran | IDEA | tran | Diamond | tran | Blowfish | prngxor | 
3des | tran | IDEA | tran | Diamond | tran | Blowfish | prngxor | 
3des | tran | IDEA | tran | Diamond | tran | Blowfish | prngxor | 
3des | tran | IDEA | tran | Diamond | tran | Blowfish | prngxor | 
3des | tran | IDEA | tran | Diamond | tran | Blowfish | prngxor | 
... about 500 more lines of the same ...

with a memorized 5 megabyte key.

And I thought 15 round Diamond with a 256 bit key was overkill worse than 
3 key triple DES!

Seriously, folks, the weakest links of most cryptosystems are not in the 
symmetric key cipher (provided you pick one of the good ones), but in the 
key management, associating people with keys, and in picking good pass 
phrases.

Peace to you.
Mike Johnson
m.p.johnson@ieee.org