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List:       linux-crypto
Subject:    Re: a question about ciphers
From:       Pascal Junod <pascal.junod () epfl ! ch>
Date:       2001-12-13 16:11:48
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On Thu, 13 Dec 2001, Jerome Etienne wrote:

> suppose you are the attacker and get data encrypted with a block cipher,
> two or more cipher texts block are equal, which information did get
> from it ?


If the encryption mode is ECB, you know that both plaintexts are equal.
If the encryption mode is CBC, you know some information about the XOR of
two plaintexts.

There exists similar attacks for OFB and CFB, which retrieve some
(Shannon) information.

A+

Pascal

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* Pascal Junod, pascal.junod@epfl.ch                                 *
* Security and Cryptography Laboratory (LASEC)                       *
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