Re: XOR and ADD subtil difference ?

From: Arnaud Carré (arnaud.carreNOSPAM_at_freesurf.fr)
Date: 11/30/04 

Date: Tue, 30 Nov 2004 16:42:30 +0100

> The "safety" of an encryption algorithm is only
> loosely connected to the primitive operations used.

totally agree.

> There is one advantage of multidigit (carrying)
> addition over unidigit addition (including bit XOR),
> namely the carries diffuse a small amount of the
> information. It's not a large effect but sometimes
> it makes the cryptanalysis harder.

so you mean is a "few little" harder for cryptanalyst to attack ADD (
modulo) than XOR ? If yes, what about the idea of custom AES modifyed using
ADD ?

I never really think about it. Hemm, I think it won't work , depend on
implementation. ( I mean, 32bits AES implementation should not produce same
data as 8bits AES implementation using ADD, maybe that's why XOR is used)

Maybe unidigit addition is used only because it's independant to internal
register data size ( 8,16,32 or more bits).

Have another idea why XOR is oftne prefered to ADD in cryptography ?