[103114] in Cypherpunks
Alleged IDEA(tm) Weakness
daemon@ATHENA.MIT.EDU (Eric Cordian)
Sun Sep 20 11:52:25 1998
From: Eric Cordian <emc@wire.insync.net>
To: cypherpunks@cyberpass.net
Date: Sun, 20 Sep 1998 10:40:03 -0500 (CDT)
In-Reply-To: <199809200308.NAA12805@avalon.qualcomm.com> from "Greg Rose" at Sep 20, 98 01:08:35 pm
Reply-To: Eric Cordian <emc@wire.insync.net>
> I think this is wrong. It claims that the problem
> in IDEA comes from the bias of the multiplication
> operation... but the multiply in IDEA is over the
> integers modulo 65537, with the 0 value
> representing 65536, not 0... this is in fact an
> unbiased operation. However I have not attempted
> to verify the rest of the logic.
Correct, multiplication by a non-zero residue modulo 65537 is a
permutation of the non-zero residues. The central notion behind IDEA is
to use this operation, which can be expressed expeditiously in terms of
the unsigned 16x16->32 multiply, as a builtin wide S-Box. This is how
IDEA manages to do strong encryption using only a few ordinary arithmetic
and logical instructions with no necessity for table lookup.
I didn't bother to read the rest of the rant.
--
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