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

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Message-ID: <4755BD0C.2060808@redhat.com>
Date:	Tue, 04 Dec 2007 14:48:12 -0600
From:	Mike McGrath <mmcgrath@...hat.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Theodore Tso <tytso@....edu>, Matt Mackall <mpm@...enic.com>,
	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?

Alan Cox wrote:
>> Here's the top 5:
>>
>>    266 28caf2c3-9766-4fe1-9e4c-d6b0ba8a0132
>>    336 810e7126-1c69-4aff-b8b1-9db0fa8aa15a
>>    402 c8dbb9d3-a9bd-4ba6-b92e-4a294ba5a95f
>>    884 06e84493-e024-44b1-9b32-32d78af04039
>>    931 e2b67e1d-e325-4740-b938-795addb45280
>>
>> The left number is times this month someone has submitted a profile with
>> that UUID.  If we take the last one as an example has come from over 800
>> IP's in the last 20 days.  It seems very unlikely that one person would
>> find his way to 800 different IP's this month.  Let me know if you'd
>> like more.
>>     
Background - Smolt runs this during its install:

/bin/cat /proc/sys/kernel/random/uuid > /etc/sysconfig/hw-uuid

For most users this would be run by the RPM %post scripts during install 
from anaconda. For some reason there are some UUID's (like those listed 
above) that come up more often then it seems they should if they are 
truly random.

-Mike
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