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

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Message-Id: <200712091606.50089.ismail@pardus.org.tr>
Date:	Sun, 9 Dec 2007 16:06:49 +0200
From:	Ismail Dönmez <ismail@...dus.org.tr>
To:	Theodore Tso <tytso@....edu>, 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 14:31:47 tarihinde Theodore Tso şunları yazmıştı:
> On Sun, Dec 09, 2007 at 08:21:16AM +0200, Ismail Dönmez wrote:
> > 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?
>
> Past a certain point /dev/urandom will stat returning results which
> are cryptographically random.  At that point, you are depending on the
> strength of the SHA hash algorithm, and actually being able to not
> just to find hash collisions, but being able to trivially find all or
> most possible pre-images for a particular SHA hash algorithm.  If that
> were to happen, it's highly likely that all digital signatures and
> openssh would be totally broken.

Thats very good news, thanks for the detailed explanation. Time to update 
common misconceptions.

Regards,
ismail

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