From: DAVESPARKS@delphi.com
Date: Thu, 14 Jul 94 22:27:35 PDT
To: cypherpunks@toad.com
Subject: Re: Triple encryption...
Message-ID: <01HEPTT89VZI9I5RDS@delphi.com>
MIME-Version: 1.0
Content-Type: text/plain


Carl Ellison (cme@tis.com) wrote:

> have you considered
>
>        des | tran | des | tran | des ?

That one's sort of your "trademark", isn't it? <g>  (TRAN is really
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.  Other than making the code bulkier by requiring the
inclusion of code for TWO crypto algorithms, and 64 bits of extra key
material, what other drawbacks would there be to such a scheme (in a
NON-commercial setting where licensing of the patented IDEA is not an
issue)?  If IDEA turns out to not be as secure as we've been led to believe,
at least it, sandwiched between two layers of TRAN shuffling, should at least
slow down a meet-in-the-middle attack on the remaining two layers of DES.

As I recall, last time we discussed this over on sci.crypt you also
advocated an additional step of "PRNGXOR".  Is that still the case?  Have
you had the opportunity to read the Eurocrypt '94 paper by Eli Biham on
triple DES modes, yet?

 /--------------+------------------------------------\
 |              |  Internet: davesparks@delphi.com   |
 | Dave Sparks  |  Fidonet:  Dave Sparks @ 1:207/212 |
 |              |  BBS:      (909) 353-9821 - 14.4K  |
 \--------------+------------------------------------/