Re: [dm-devel] [PATCH] dm-crypt: disable block encryption with arc4

[Sebastian Andrzej Siewior <linux-crypto ml breakpoint cc>]

* Mikulas Patocka | 2010-01-26 07:27:18 [-0500]:

>> yes, I think it is better.
>> (...and I just forgot to add that test to dm-crypt after that suggestion.)
>> 
>> Milan
>
>Hmm, there is salsa20 that has block size 1, larger initialization 
>vectors, and can be used to encrypt disks (although salsa20 doesn't 
>currently work with dm-crypt, because it doesn't accept "ecb(), cbc(), 
>etc." chaining modes --- but if you remove the chaining mode manually, it 
>works).
>
>You should rather add a flag CRYPTO_ALG_CHANGES_STATE to determine that a 
>cipher can't be used to encrypt disks.

Just because it will work does not make it a good idea.

SALSA20 is a stream cipher not a block cipher.
Block ciphers are used to encrypt data.
Stream ciphers are used to create one time pads, a set of encryption
keys, ...
There are block modes like CTR which can turn a block cipher into a
stream cipher. Those should not be used for disk encryption as well.

>
>Mikulas

Sebastian