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

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Message-Id: <1197099477.20786.149.camel@perihelion>
Date:	Sat, 08 Dec 2007 02:37:57 -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 Wed, 2007-12-05 at 09:49 -0500, Theodore Tso wrote:
> On Wed, Dec 05, 2007 at 08:26:19AM -0600, Mike McGrath wrote:
> >
> > Ok, whats going on here is an issue with how the smolt RPM installs the 
> > UUID and how Fedora's Live CD does an install.  It's a complete false alarm 
> > on the kernel side, sorry for the confusion.
> 
> 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.

Jon.


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