linux-kernel - Re: Entropy sources (was: /dev/random

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Date:   Thu, 25 Aug 2016 19:35:29 -0400
From:   Sandy Harris <sandyinchina@...il.com>
To:     "H. Peter Anvin" <hpa@...or.com>
Cc:     Jeffrey Walton <noloader@...il.com>, linux-crypto@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        "Theodore Ts'o" <tytso@....edu>
Subject: Re: Entropy sources (was: /dev/random - a new approach)

On Thu, Aug 25, 2016 at 5:30 PM, H. Peter Anvin <hpa@...or.com> wrote:

> The network stack is a good source of entropy, *once it is online*.
> However, the most serious case is while the machine is still booting,
> when the network will not have enabled yet.
>
>         -hpa

One possible solution is at:
https://github.com/sandy-harris/maxwell

A small (< 700 lines) daemon that gets entropy from timer imprecision
and variations in time for arithmetic (cache misses, interrupts, etc.)
and pumps it into /dev/random. Make it the first userspace program
started and all should be covered. Directory above includes a PDF doc
with detailed rationale and some discussion of alternate solutions.

Of course if you are dealing with a system-on-a-chip or low-end
embedded CPU & the timer is really inadequate, this will not work
well. Conceivably well enough, but we could not know that without
detailed analysis for each chip in question.