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

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Message-ID: <2c0942db0712111202p2efea8d7j21a04c8ec2ead04b@mail.gmail.com>
Date:	Tue, 11 Dec 2007 12:02:14 -0800
From:	"Ray Lee" <ray-lk@...rabbit.org>
To:	"Phillip Susi" <psusi@....rr.com>
Cc:	"Theodore Tso" <tytso@....edu>, "Matt Mackall" <mpm@...enic.com>,
	"Marc Haber" <mh+linux-kernel@...schlus.de>,
	"Eric Dumazet" <dada1@...mosbay.com>,
	"Alan Cox" <alan@...rguk.ukuu.org.uk>,
	"Adrian Bunk" <bunk@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: Why does reading from /dev/urandom deplete entropy so much?

On Dec 11, 2007 11:46 AM, Phillip Susi <psusi@....rr.com> wrote:
> Theodore Tso wrote:
> > Note that even paranoid applicatons should not be using /dev/random
> > for session keys; again, /dev/random isn't magic, and entropy isn't
> > unlimited. Instead, such an application should pull 16 bytes or so,
> > and then use it to seed a cryptographic random number generator.
>
> What good does using multiple levels of RNG do?  Why seed one RNG from
> another?  Wouldn't it be better to have just one RNG that everybody
> uses?

Not all applications need cryptographically secure random numbers.
Sometimes, you just want a random number to seed your game RNG or a
monte carlo simulator.
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