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The following archive was created by hippie-mail 7.98617-22 on Fri Aug 21 1998 - 17:20:31 ADT
Bruce Schneier (schneier@counterpane.com)
Thu, 16 Jul 1998 22:39:45 -0500
At 11:37 PM 7/16/98 -0400, Perry E. Metzger wrote:
>
>Bruce Schneier writes:
>> My main complaint about MARS is that I cannot keep the entire design
>> in my head. One of the Twofish design goals was to create a cipher
>> that could be easily memorized. I find that I can imagine new
>> attacks, and carry out analysis, easier if the cipher is easy to
>> conceptualize. With MARS I am continually going back to the paper
>> to remember how something works. I am much less likely to find good
>> analyses.
>
>I do understand the complaint -- it makes some considerable sense.
>
>It certainly is a rather complex cipher. Of course, the design
>document explains the reason behind all the complexities. The
>observations about attempting to thwart early and late round attacks
>by special mechanisms seemed to warrant some of the complexity
>(although the use of whitening in other designs at least weakly
>addresses this as well.)
Whitening basically does the work of one round, at considerable less
latency cost.
>> >Coolest of the recent AES batch seemed to be RC6, but the paper also
>> >left a bit to be desired in the way of transparency in describing
>> >attacks. I liked the design methodology description, though.
>>
>> Data dependent rotations worry me,
>
>They seem to be another new trend in several designs, though,
>including MARS. Now that techniques have been pioneered to assure that
>the rotations don't only depend on the low order bits of the data
>(done in very different ways in both MARS and RC6), I think it may be
>an effective new tool (although I obviously have no proof that the
>technique isn't vulnerable.)
But in RC5 that's all you've got. In RC6 there is a little more, but not
much.
Bruce
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Bruce Schneier, President, Counterpane Systems Phone: 612-823-1098
101 E Minnehaha Parkway, Minneapolis, MN 55419 Fax: 612-823-1590
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The following archive was created by hippie-mail 7.98617-22 on Fri Aug 21 1998 - 17:20:31 ADT