[PATCH 07/10] password: add pbkdf2 support

[Jean-Christophe PLAGNIOL-VILLARD]

On 12:05 Mon 16 Mar     , Jan Lübbe wrote:
> On Mo, 2015-03-16 at 12:01 +0100, Jean-Christophe PLAGNIOL-VILLARD wrote:
> > On 11:49 Mon 16 Mar     , Jan Lübbe wrote:
> > > On Mo, 2015-03-16 at 11:15 +0100, Jean-Christophe PLAGNIOL-VILLARD wrote:
> > > > We will use "barebox_password" as salt and 10000 round to generate a
> > > > 64 bytes key.
> > > 
> > > The purpose of a salt is to protect a against dictionary or
> > > rainbow-table (precomputed) attacks. That means that the Salt must be
> > > randomly generated and saved with the password.
> > This will be a enough stong enven with static one to protect against
> > reverse hack for barebox protection
> > 
> > Use a 32 byte pass try to do an attack agaist dictionary.
> > it will take you more than 10 years to break it
> > > 
> > > For setting a new password in barebox, even a low entropy salt will make
> > > attacks significantly more expensive. So we should add some entropy from
> > > user interaction timing in that case.
> > yes we could do this too
> > > 
> > > For hashing a password at compile time, we should get the salt from the
> > > host system.
> > yes
> > 
> > do we really need it?
> 
> Yes, definitely. We must use the algorithms as they are intended to be
> used.
> 
> If we try to move users away from RSA2048 because it will be vulnerable
> in the future, we should not go against established practice for
> password salts by hard-coding it. 
I'm not against it but with the barebox entropy did not see the point to use
it.

so how do we generate the salt? what length

Personnaly I'll prefer

a random 64 bytes | sha256 | take first 32bytes. | pbkdf2 10000 round

result a 64 bytes password file <salt 32 byes><key 32 bytes>

Best Regards,
J.