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

[Mikulas Patocka <mpatocka redhat com>]

> >>> This patch disables the use of arc4 on block devices.
> >>
> >> arc4 again. it is simply not a block cipher:-)
> >>
> >> This should be solved inside cryptoAPI and not blacklist it in dm-crypt,
> >> see that thread
> >> http://article.gmane.org/gmane.linux.kernel.cryptoapi/3441
> > 
> > I some how remember Herbert saying to test for block size > 1. Wouldn't
> > this be acceptable to block all stream cipher in one go?
> 
> 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.

Mikulas