Re: [Buildroot] [PATCH v2] package/urandom-scripts: hash old seed with new seed when saving

["Yann E. MORIN" <yann.morin.1998@free.fr>]

David, All,

On 2022-03-24 10:25 +0000, David Laight spake thusly:
> From: Yann E. MORIN
> > On 2022-03-24 09:15 +0000, David Laight spake thusly:
> > > From: Yann E. MORIN
> > > > +Peter: candidate for backporting as a security fix
> > > Probably not - the security fix is the code that actually
> > > initialises the RNG.
> > Not sure I understood... As Jason explained, we have so far been saving
> > a seed from an RNG that is probably partially deterministic; that is the
> > security issue.
> I'm pretty sure the seed is also saved during shutdown.
> So a normal startup doesn't rely on the seed saved by the startup script.
> (Although is would be better to use a background script
> to save after (say) 30 minutes of operation.)

The problem is that a lot, if not most, embedded devices are never
properly shut-down; instead, they are, intentionally or not, brutally
electrically powered off.

In that case, the seed that is saved at boot is what is going to be
reused on the next boot. And currently, that seed is weak, because the
output of the RNG at  boot is mostly predicatble.

Regards,
Yann E. MORIN.

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