To: linux-kernel@vger.kernel.org
From: Jon Masters <jonathan@jonmasters.org>
Subject: Re: Why does reading from /dev/urandom deplete entropy so much?
Date: Sun, 09 Dec 2007 01:52:05 -0500
Organization: World Organi[sz]ation Of Broken Dreams
Message-ID: <1197183090.12636.15.camel@perihelion>
References: <20071204114125.GA17310@torres.zugschlus.de>
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	 <200712090010.10362.ismail@pardus.org.tr>
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On Sun, 2007-12-09 at 06:21 +0100, Willy Tarreau wrote:

> Wouldn't it be possible to mix the data with the pid+uid of the reading
> process so that even if another one tries to collect data from urandom,
> he cannot predict what another process will get ? BTW, I think that the
> tuple (pid,uid,timestamp of open) is unpredictable and uncontrollable
> enough to provide one or even a few bits of entropy by itself.

Timestamp perhaps, but pid/uid are trivially guessable in automated
environments, such as LiveCDs. And if you're also running on an embedded
system without a RTC (common, folks like to save a few cents) then it's
all pretty much "trivially" guessable on some level.

Jon.


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