Re: [Buildroot] [PATCH v3] package/urandom-scripts: actually credit seed files via seedrng

[David Laight <David.Laight@ACULAB.COM>]

From: Jason A. Donenfeld
> Sent: 01 April 2022 10:23
> 
> On 4/1/22, David Laight <David.Laight@aculab.com> wrote:
> > I used the following small program instead of dd to credit the entropy.
> 
> Not a safe idea; will lead to problems and footguns. Doesn't handle
> safe fsync'd deletion of used seeds and safe sequencing. Doesn't
> handle hashing old seed with new seed. Ignores much of the discussion
> that lead to seedrng's design.

But it does exactly what the old scripts thought they were doing
and is far better that just using dd.

I'm not even sure that trying to save a 'new seed' in the
startup script is a good idea at all.
The new seed is very likely to just be a permutation of the
old seed - since little extra 'entropy' can have been added.
So while it may stop complete reproducibility I'm not at
all sure it is cryptographically sound at all.

If you can't rely on saving entropy at shutdown, then using
(the equivalent of) a cron job to save every hour (or so)
is probably useful.

	David

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