Subject: Re: Why does reading from /dev/urandom deplete entropy so much?
From: Jon Masters <jonathan@jonmasters.org>
To: Theodore Tso <tytso@mit.edu>
Cc: Mike McGrath <mmcgrath@redhat.com>, Matt Mackall <mpm@selenic.com>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>, Ray Lee <ray@madrabbit.org>,
       Adrian Bunk <bunk@kernel.org>,
       Marc Haber <mh+linux-kernel@zugschlus.de>, linux-kernel@vger.kernel.org
In-Reply-To: <20071208173204.GI17037@thunk.org>
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Organization: World Organi[sz]ation Of Broken Dreams
Date: Sat, 08 Dec 2007 12:45:27 -0500
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On Sat, 2007-12-08 at 12:32 -0500, Theodore Tso wrote:
> On Sat, Dec 08, 2007 at 02:37:57AM -0500, Jon Masters wrote:
> > > BTW, You may be better off using "uuidgen -t" to generate the UUID in
> > > the smolt RPM, since that will use 12 bits of randomness from
> > > /dev/random, plus the MAC, address and timestamp.  So even if there is
> > > zero randomness in /dev/random, and the time is January 1, 1970, at
> > > least the MAC will contribute some uniqueness to the UUID.
> > 
> > I haven't checked how uuidgen uses the MAC, but I would suggest that
> > that is not something Fedora should jump at doing - although it would
> > help ensure unique UUIDs, it also contributes to the tinfoil hat
> > responses that usually come up with things like smolt.
> 
> Huh?  What's the concern?  All you are submitting is a list of
> hardware devices in your system.  That's hardly anything sensitive....

Right, but the MAC is globally unique (well, that's normally true) so it
is an identifiable user characteristic, moreso than just a list of PCI
device IDs sitting on a particular bus. It's silly, but there it is.

Jon.


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