linux-kernel - Re: Seeding /dev/random not working

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Message-ID: <20070529141456.GC5840@ucw.cz>
Date:	Tue, 29 May 2007 14:14:56 +0000
From:	Pavel Machek <pavel@....cz>
To:	Theodore Tso <tytso@....edu>, M Macnair <mmacnair@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Seeding /dev/random not working

Hi!

> > I have two embedded boards (one ARM, one PowerPC), running two
> > different versions of 2.6.  They have no hard drives, keyboards or
> > mice.  They each have a NIC, but I understand these make no
> > contribution to the entropy pool.
> > 
> > 	if [ -f $random_seed ]; then
> > 		cat $random_seed >/dev/urandom  # should seed the pool
> > 	fi
> > 	dd if=/dev/urandom of=$random_seed count=1 2>/dev/null # save some
> > data from urandom for next boot
> >
> > I have rebooted my boards many times, and after each boot I read the
> > contents of $random_seed.  Whilst it does not happen every time, the
> > contents of $random_seed are /often the same/.  To give you a feel:
> > rebooted 11 times, got a total of 3 different outputs.
> 
> Ok, so this is telling me a couple of things.  First of all, if you're
> only getting three outputs, it means that you don't have any
> peripherals feeding entropy into the system from the boot sequence.
> Without any hard drives, keyboards or mice, and a NIC whose device
> driver hasn't been configured to feed entropy, you're definitely
> hosed.

Can we get at least time-of-boot from rtc clock to the pool? We really
should not be getting identical outputs...

							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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