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Date:      Mon, 10 Sep 2012 13:32:10 -0700
From:      Arthur Mesh <arthurmesh@gmail.com>
To:        Doug Barton <dougb@FreeBSD.org>
Cc:        Arthur Mesh <arthurmesh@gmail.com>, freebsd-rc@freebsd.org, obrien@freebsd.org, freebsd-security@freebsd.org, RW <rwmaillists@googlemail.com>, Dag-Erling Sm?rgrav <des@des.no>, Xin Li <delphij@delphij.net>
Subject:   Re: svn commit: r239569 - head/etc/rc.d
Message-ID:  <20120910203210.GB90314@x96.org>
In-Reply-To: <504E4765.1020909@FreeBSD.org>
References:  <20120906174247.GB13179@dragon.NUXI.org> <20120906230157.5307a21f@gumby.homeunix.com> <20120906224703.GD89120@x96.org> <20120907015157.GA29497@server.rulingia.com> <20120910135218.GA68128@dragon.NUXI.org> <504E343A.4020802@FreeBSD.org> <86pq5tu1zr.fsf@ds4.des.no> <504E3DAB.3090000@FreeBSD.org> <86fw6pu0l0.fsf@ds4.des.no> <504E4765.1020909@FreeBSD.org>

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On Mon, Sep 10, 2012 at 01:02:45PM -0700, Doug Barton wrote:
> > I was exaggerating a bit - but my reasoning was that since it hasn't
> > blown up in our faces yet, it's probably subtle enough to require a
> > large number of samples.
> 
> 
> If I were Arthur, here is how I would test the "replay attack" assertion:
> 
> 1. Install a virgin system with everything as it was before David's
> first commit, and let it run for 24 hours with all the defaults intact.
> Ideally, have it do something over the network periodically to make sure
> that some kind of entropy is harvested from the network drivers. Run
> 'find / -name SASLKASDJKL' to make sure you get some from the disk
> drivers too.
> 2. Disable the cron job for the /var/db/entropy script, and comment out
> the writing of /entropy at shutdown time in /etc/rc.d/random.
> 3. Write a script to reboot, and once the system is fully booted do 'dd
> if=/dev/random of=saved-random-out.$i count=4096' then reboot again
> immediately. Values of i from 1 to 10,000 ought to do it.
> 4. sha256 the saved-random-out files and see how many duplicates there are.

This test doesn't prove anything useful for the reason des@ outlined.

To summarize, I have provided my findings and reasoning multiple times.
I've sent a separate report with pointers to problematic code of how
entropy is consumed by yarrow to secteam@.

You keep asking for empirical proof of my claims.

There are two claims that I make:

1) entropy isn't fully consumed by yarrow all the time - for this I have
empirical proof.

2) reusing entropy seeds is a bad thing - for this I don't have
empirical proof. But I have Bruce Schneier's word.

Take it or leave it.



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