lkml.org 
[lkml]   [2019]   [Oct]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] KEYS: asym_tpm: Switch to get_random_bytes()
On Thu, Oct 17, 2019 at 09:04:40PM +0300, Jarkko Sakkinen wrote:
> On Wed, Oct 16, 2019 at 03:10:29PM -0400, James Bottomley wrote:
> > On Wed, 2019-10-16 at 19:25 +0300, Jarkko Sakkinen wrote:
> > > On Wed, Oct 16, 2019 at 08:34:12AM -0400, James Bottomley wrote:
> > > > reversible ciphers are generally frowned upon in random number
> > > > generation, that's why the krng uses chacha20. In general I think
> > > > we shouldn't try to code our own mixing and instead should get the
> > > > krng to do it for us using whatever the algorithm du jour that the
> > > > crypto guys have blessed is. That's why I proposed adding the TPM
> > > > output to the krng as entropy input and then taking the output of
> > > > the krng.
> > >
> > > It is already registered as hwrng. What else?
> >
> > It only contributes entropy once at start of OS.
>
> Ok.
>
> > > Was the issue that it is only used as seed when the rng is init'd
> > > first? I haven't at this point gone to the internals of krng.
> >
> > Basically it was similar to your xor patch except I got the kernel rng
> > to do the mixing, so it would use the chacha20 cipher at the moment
> > until they decide that's unsafe and change it to something else:
> >
> > https://lore.kernel.org/linux-crypto/1570227068.17537.4.camel@HansenPartnership.com/
> >
> > It uses add_hwgenerator_randomness() to do the mixing. It also has an
> > unmixed source so that read of the TPM hwrng device works as expected.
>
> Thinking that could this potentially racy? I.e. between the calls
> something else could eat the entropy added?

Also, what is wrong just taking one value from krng and mixing
it with a value from TPM RNG where needed? That would be non-racy
too.

/Jarkko

\
 
 \ /
  Last update: 2019-10-21 13:41    [W:0.164 / U:5.804 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site