Re: PROBLEM: AES cryptoloop corruption under recent -mm kernels

[Mark Borgerding]

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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