linux-kernel - Re: Why does reading from /dev/urandom deplete entropy so much?

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Date:	Sat, 08 Dec 2007 12:54:13 -0500
From:	Jon Masters <jonathan@...masters.org>
To:	Theodore Tso <tytso@....edu>
Cc:	Mike McGrath <mmcgrath@...hat.com>, Matt Mackall <mpm@...enic.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ray Lee <ray@...rabbit.org>, Adrian Bunk <bunk@...nel.org>,
	Marc Haber <mh+linux-kernel@...schlus.de>,
	linux-kernel@...r.kernel.org
Subject: Re: Why does reading from /dev/urandom deplete entropy so much?


On Sat, 2007-12-08 at 12:49 -0500, Theodore Tso wrote:
> On Sat, Dec 08, 2007 at 11:33:57AM -0600, Mike McGrath wrote:
> >> Huh?  What's the concern?  All you are submitting is a list of
> >> hardware devices in your system.  That's hardly anything sensitive....
> >
> > We actually had a very vocal minority about all of that which ended up 
> > putting us in the unfortunate position of generating a random UUID instead 
> > of using a hardware UUID from hal :-/
> 
> Tinfoil hat responses indeed!  Ok, if those folks are really that
> crazy, my suggestion then would be to do a "ifconfig -a > /dev/random"
> before generating the UUID, and/or waiting until you just about to
> send the first profile, and/or if you don't yet have a UUID,
> generating it at that very moment.  The first will mix in the MAC
> address into the random pool, which will help guarantee uniqueness,
> and waiting until just before you send the result will mean it is much
> more likely that the random pool will have collected some entropy from
> user I/O, thus making the random UUID not only unique, but also
> unpredictable.

I do like that idea, and it could be combined with the DMI data for the
system containing things like asset tracking numbers, etc. Could use HAL
to generate a UUID based on hardware IDs and feed that in as entropy ;-)

Jon.


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