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 12:05
> 
> On 4/1/22, James Hilliard <james.hilliard1@gmail.com> wrote:
> > I should add that I do also think this should be upstreamed to busybox,
> > which
> > will also reduce the amount of duplicate work as busybox is commonly used
> > across many distros.
> 
> I'll work on that. And hopefully David won't sabotage it with his
> "it's only 10 lines!" stuff.

:-)

Busybox tends to care about code size.
You really want to roll-up the unrolled loop in blakes2.
Performance really doesn't matter here.

In any case, don't new kernels just 'stir' the new entropy into
input pool?
So feeding in non-random data doesn't really make the output
any worse?
So you could add the saved entropy, force a reseed of the output
generator, and then save data from /dev/urandom - which now
contains any entropy collected since boot and the saved seed.
No need for any cryprographic code in userspace??

The old kernel code is just too horrid to think about.
IIRC the output generator is just and xor of several LFSR
and so is completely and trivially reversable.
(One of the random number generators did that.)
And the input pool tries to count bits in and out instead
of 'stirring' input data into some data structure.
So feed it non-random data and it discards the old random
data it had.

How much state does the blakes2 input pool have?
I'd have thought you'd want the input pool to have
much more state than the output generator?

	David

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