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

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Message-Id: <1197135927.6899.13.camel@perihelion>
Date:	Sat, 08 Dec 2007 12:45:27 -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 12:32 -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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