[dm-crypt] Switch to XTS mode for LUKS in cryptsetup in 1.6.0 (Was Re: [ANNOUNCE] cryptsetup 1.6.0-rc1)

Arno Wagner arno at wagner.name
Sat Jan 5 18:20:34 CET 2013


On Fri, Jan 04, 2013 at 11:39:43PM +0100, Milan Broz wrote:
> On 01/04/2013 11:05 PM, Arno Wagner wrote:
[...]
> > Hmm, reading this again, and the discussion comments by 
> > Schneier, maybe we should use AES128 as default. 
> > AES256 might indeed be somewhat weaker than AES128. 
> 
> But please note this is from 2009. There are some new recent
> papers related even to AES128.
> 
> To cite the same source...
> http://www.schneier.com/blog/archives/2011/08/new_attack_on_a_1.html
> 
> Dunno. aes128-xts is perhaps enough (and the keyslot size remains
> the same).
> 
> > 
> > Not that either can be broken at this time. 
> > 
> > One idea: With AES256+XTS, the keyslot-area is larger.
> > If somebody wants to re-encrypt AES256+CBC in place,
> > they would need to use AES128+XTS anyways. Correct?
> 
> reencrypt tool supports data shift, so you just need to add some
> space or reduce fs in advance. But yes, it is more complicated.

What does RHEL use and recommend? Do they always use
AES256-XTS or is AES128-XTS offered as an option (not when
douing this manually via commandline). I think there would
be some benefit to have the same defauls in distro-independent
cryptsetup.
 
I think the security levels of AES128 and AES256 are not
different enough that we should ecide on that alone or
even as main criterium. 

> > That would be a second reason to use AES128.
> > 
> > Well, things are never simple when security is concerned...
> 
> I think there is only one simple situation in cryptography...
> Once is something broken, it remains broken forever :-)

Yes, indeed :-)

Arno
-- 
Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno at wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
----
One of the painful things about our time is that those who feel certainty
are stupid, and those with any imagination and understanding are filled
with doubt and indecision. -- Bertrand Russell


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