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SubjectRe: PROBLEM: AES cryptoloop corruption under recent -mm kernels
James Morris wrote:

>On Fri, 16 Jan 2004, Mark Borgerding wrote:
>
>
>
>> From looking through the cryptoloop code, it looks like the IV for CBC
>>mode is always the sector index. It seems this could be weak against
>>chosen plaintext attacks, as well as allowing an attacker to know which
>>cipher blocks started any changes between two snapshots of the
>>ciphertext. I discuss ECB, since I wouldn't consider using it.
>>
>>
>
>Eli Biham has suggested encrypting the sector numbers, see
>http://people.redhat.com/jmorris/crypto/cryptoloop_eli_biham.txt
>
>
>
>- James
>
>

This does not defend against a dictionary attack.

The IV is still deterministic for a given sector and hypothesized
password.
Thus the ciphertext for a given plaintext at that sector is still
deterministic.

Thinking of it another way, this is equivalent to CBC mode having two
IVs: the first one being the sector number, the second a block of zeros.


- Mark

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