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

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Date:	Tue, 11 Dec 2007 00:06:43 +0100
From:	Marc Haber <mh+linux-kernel@...schlus.de>
To:	Matt Mackall <mpm@...enic.com>
Cc:	Eric Dumazet <dada1@...mosbay.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Adrian Bunk <bunk@...nel.org>, linux-kernel@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: Why does reading from /dev/urandom deplete entropy so much?

On Sun, Dec 09, 2007 at 10:16:05AM -0600, Matt Mackall wrote:
> On Sun, Dec 09, 2007 at 01:42:00PM +0100, Marc Haber wrote:
> > On Wed, Dec 05, 2007 at 03:26:47PM -0600, Matt Mackall wrote:
> > > The distinction between /dev/random and /dev/urandom boils down to one
> > > word: paranoia. If you are not paranoid enough to mistrust your
> > > network, then /dev/random IS NOT FOR YOU. Use /dev/urandom.
> > 
> > But currently, people who use /dev/urandom to obtain low-quality
> > entropy do a DoS for the paranoid people.
> 
> Not true, as I've already pointed out in this thread.

I must have missed this. Can you please explain again? For a layman it
looks like a paranoid application cannot read 500 Bytes from
/dev/random without blocking if some other application has previously
read 10 Kilobytes from /dev/urandom.

Greetings
Marc

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