Re: [dm-crypt] different default key sizes for CREATE and LUKSFORMAT

[Arno Wagner <arno@wagner.name>]

On Wed, Nov 18, 2009 at 02:26:10PM +0100, Milan Broz wrote:
> On 11/18/2009 12:20 PM, Milan Broz wrote:
> > For default LUKS header hash:
> > 
> > - default is SHA1
> > 
> > switching to another (probably SHA-256?) means complete incompatibility
> > with all cryptsetup <1.1.x, this need some time when all most distros
> > use new cryptsetup.
> > No need to hurry, there is no problem with SHA1 in this application
> > of hash function.
> 
> Also I think we can increase MK digest iterations
> (default is now 10, increasing it to 1000 should not cause any performance
> problems. Just make the possible attack to MK digest more complicated
> if some hash is completely broken in future.)
> 
> Does this make sense of it is not needed?

If I understand this correctly, this is the "iteration-count" 
parameter to PBKDF2. If so, then RFC 2898 recommends a minimum 
count of 1000 anyways. This is hovever not protection against 
a broken hash, as even a very weak hash should be extremely 
hard to break when iterated 10 times. The main purpose of this 
parameter is to make exhaustive search more expensive. I think 
this should definitely go up to 1000.

Arno
-- 
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno@wagner.name 
GnuPG:  ID: 1E25338F  FP: 0C30 5782 9D93 F785 E79C  0296 797F 6B50 1E25 338F
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