Re: XOR and ADD subtil difference ?

From: Wannabee (no_at_mail.thanks)
Date: 11/30/04 

Date: Tue, 30 Nov 2004 12:54:37 +0200

"Arnaud Carré" wrote
> Hi all,
>
> I wonder if there is a "security" difference between XOR and ADD ? I mean,
> let's take random-number generator using external entropy source. Some of
> them uses XOR to mix entropy to current state, some of them use XOR.

I'm not quite sure if I understand you correct.

There is nothing wrong with XOR. There may be something wrong with the
values you use to XOR with. To ADD you need a modulus (implicit or
explicit). It is more complicated and it doesn't give any additional value.
XOR in simple and efficient.

>Ex,
> quote from the good TrueCrypt :
>
> 'Random values are written to the pool by adding (not by replacing the old
> values in the pool).'
> Do you thing guys security should be changed if XOR is used ? Could you
> explain a bit ? ( whatever the answer is yes or no (I guess it's "no" but
I
> don't know why))

I think that quote simply means that the number of values in the pool
increases. I don't think it implies that some addition (modulo X) is
performed to those old values in the pool.

> Other: AES uses plenty of XOR like many block cyphers. ( let's say on
32bits
> integer in 32bits implementation). What do you think of the security of a
> "modifyed" AES using ADD instead of XOR ??

You mean ADD modulo something? ADD modulo what? ADD modulo 2^32 ?

Relevant Pages

  • Re: XOR and ADD subtil difference ?
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    ... I wonder if there is a "security" difference between XOR and ADD? ... let's take random-number generator using external entropy source. ...
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