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

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Message-Id: <200712090821.16483.ismail@pardus.org.tr>
Date:	Sun, 9 Dec 2007 08:21:16 +0200
From:	Ismail Dönmez <ismail@...dus.org.tr>
To:	Theodore Tso <tytso@....edu>
Cc:	Adrian Bunk <bunk@...nel.org>, Bill Davidsen <davidsen@....com>,
	Marc Haber <mh+linux-kernel@...schlus.de>,
	linux-kernel@...r.kernel.org
Subject: Re: Why does reading from /dev/urandom deplete entropy so much?

Sunday 09 December 2007 01:46:12 tarihinde Theodore Tso şunları yazmıştı:
> On Sun, Dec 09, 2007 at 12:10:10AM +0200, Ismail Dönmez wrote:
> > > As long as /dev/random is readable for all users there's no reason to
> > > use /dev/urandom for a local DoS...
> >
> > Draining entropy in /dev/urandom means that insecure and possibly not
> > random data will be used and well thats a security bug if not a DoS bug.
>
> Actually in modern 2.6 kernels there are two separate output entropy
> pools for /dev/random and /dev/urandom.  So assuming that the
> adversary doesn't know the contents of the current state of the
> entropy pool (i.e., the RNG is well seeded with entropy), you can read
> all you want from /dev/urandom and that won't give an adversary
> successful information to attack /dev/random.

My understanding was if you can drain entropy from /dev/urandom any futher 
reads from /dev/urandom will result in data which is not random at all. Is 
that wrong?

Regards,
ismail

-- 
Never learn by your mistakes, if you do you may never dare to try again.
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