From: "Mark M." <markm@voicenet.com>
Date: Fri, 19 Jul 1996 07:11:48 +0800
To: Jean-Francois Avon <jf_avon@citenet.net>
Subject: Re: SecureDrive(IDEA), Realdeal and plaintext attack
In-Reply-To: <9607181432.AB05188@cti02.citenet.net>
Message-ID: <Pine.LNX.3.94.960718144353.370A-100000@gak>
MIME-Version: 1.0
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On Thu, 18 Jul 1996, Jean-Francois Avon wrote:

> IDEA is reputed to be resistant against known plaintext attacks.
> But I did not read about wether or not it is resistant to 
> several-plaintexts (?choosen plaintext) attack.
> 
> If the sectors were not salted, each zeroed sectors would translate in 
> an identical way on the encrypted disk.  So, there would be only one 
> cyphertext-plaintext pair repeated over many empty sectors.
> 
> If you salt the encryptor, there are many different cyphertexts 
> corresponding to one single plaintext.
> 
> Can the salt be figured out by an attacker?

It doesn't matter whether an attacker knows the salt.  Sectors that are zeroed
are indistinguishable from secrtors that have data.  An attacker wouldn't know
which sectors are composed of zeroes.

- -- Mark

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