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

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Date:	Tue, 29 May 2007 22:06:08 +0200
From:	Folkert van Heusden <folkert@...heusden.com>
To:	Pavel Machek <pavel@....cz>, Theodore Tso <tytso@....edu>,
	M Macnair <mmacnair@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: Seeding /dev/random not working

> > > 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...

And add readings from lm-sensors as well? I guess harddisk and cpu
temperatures (lower bits) and such are pretty random?


Folkert van Heusden

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