From: Eric Dumazet <dada1@cosmosbay.com>
To: Marc Haber <mh+linux-kernel@zugschlus.de>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Why does reading from /dev/urandom deplete entropy so much?
Date: Tue, 04 Dec 2007 15:16:53 +0100 [thread overview]
Message-ID: <47556155.90006@cosmosbay.com> (raw)
In-Reply-To: <20071204114125.GA17310@torres.zugschlus.de>
Marc Haber a écrit :
> While debugging Exim4's GnuTLS interface, I recently found out that
> reading from /dev/urandom depletes entropy as much as reading from
> /dev/random would. This has somehow surprised me since I have always
> believed that /dev/urandom has lower quality entropy than /dev/random,
> but lots of it.
>
> This also means that I can "sabotage" applications reading from
> /dev/random just by continuously reading from /dev/urandom, even not
> meaning to do any harm.
>
> Before I file a bug on bugzilla, can I ask why /dev/urandom wasn't
> implemented as a PRNG which is periodically (say, every 1024 bytes or
> even more) seeded from /dev/random? That way, /dev/random has a much
> higher chance of holding enough entropy for applications that really
> need "good" entropy.
>
> Entropy depletion has become an issue on Linux systems since the
> network was removed from the group of entropy sources a few years ago.
> Of the around 20 Linux systems that I currently have root privileges
> on, only two have a hardware RNG.
>
Some network drivers still feed entropy pools :
$ find drivers/net | xargs grep -n IRQF_SAMPLE_RANDOM
drivers/net/mv643xx_eth.c:1336: IRQF_SHARED |
IRQF_SAMPLE_RANDOM, dev->name, dev);
drivers/net/3c527.c:437: err = request_irq(dev->irq,
&mc32_interrupt, IRQF_SHARED | IRQF_SAMPLE_RANDOM, DRV_NAME, dev);
drivers/net/xen-netfront.c:1371:
IRQF_SAMPLE_RANDOM, netdev->name,
drivers/net/macb.c:1131: err = request_irq(dev->irq,
macb_interrupt, IRQF_SAMPLE_RANDOM,
drivers/net/tg3.c:7268: flags = IRQF_SAMPLE_RANDOM;
drivers/net/tg3.c:7273: flags = IRQF_SHARED | IRQF_SAMPLE_RANDOM;
drivers/net/tg3.c:7291: IRQF_SHARED |
IRQF_SAMPLE_RANDOM, dev->name, dev);
drivers/net/qla3xxx.c:3648: unsigned long irq_flags =
IRQF_SAMPLE_RANDOM | IRQF_SHARED;
drivers/net/3c523.c:292: ret = request_irq(dev->irq,
&elmc_interrupt, IRQF_SHARED | IRQF_SAMPLE_RANDOM,
drivers/net/cris/eth_v10.c:704: IRQF_SAMPLE_RANDOM,
cardname, (void *)dev)) {
drivers/net/atl1/atl1_main.c:1967: int irq_flags = IRQF_SAMPLE_RANDOM;
drivers/net/niu.c:4647: IRQF_SHARED |
IRQF_SAMPLE_RANDOM,
drivers/net/netxen/netxen_nic_main.c:866:
IRQF_SHARED|IRQF_SAMPLE_RANDOM, netdev->name,
drivers/net/ibmlana.c:784: result = request_irq(priv->realirq,
irq_handler, IRQF_SHARED | IRQF_SAMPLE_RANDOM, dev->name, dev);
So I guess you could patch your kernel to get more entropy sources (even
if they are not *perfect* for some purists)
> What can I do to keep sufficiently high entropy pools even if I read
> from /dev/urandom more than once in a while?
>
> Greetings
> Marc
>
>
next prev parent reply other threads:[~2007-12-04 14:17 UTC|newest]
Thread overview: 77+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-12-04 11:41 Why does reading from /dev/urandom deplete entropy so much? Marc Haber
2007-12-04 14:16 ` Eric Dumazet [this message]
2007-12-04 16:18 ` Adrian Bunk
2007-12-04 16:47 ` Alan Cox
2007-12-04 18:17 ` Eric Dumazet
2007-12-05 21:26 ` Matt Mackall
2007-12-06 7:02 ` Eric Dumazet
2007-12-06 16:09 ` Matt Mackall
2007-12-09 12:42 ` Marc Haber
2007-12-09 16:16 ` Matt Mackall
2007-12-10 23:06 ` Marc Haber
2007-12-10 23:35 ` Matt Mackall
2007-12-11 1:34 ` Theodore Tso
2007-12-11 19:46 ` Phillip Susi
2007-12-11 20:02 ` Ray Lee
2007-12-12 5:34 ` David Schwartz
2007-12-04 16:54 ` Ray Lee
2007-12-04 16:55 ` Alan Cox
2007-12-04 18:02 ` Matt Mackall
2007-12-04 19:50 ` Theodore Tso
2007-12-04 20:36 ` Matt Mackall
2007-12-04 20:40 ` Alan Cox
2007-12-04 20:48 ` Mike McGrath
2007-12-04 21:54 ` Matt Mackall
2007-12-04 22:03 ` Theodore Tso
2007-12-04 22:12 ` Mike McGrath
2007-12-04 22:28 ` Matt Mackall
2007-12-04 21:08 ` Matt Mackall
2007-12-04 21:18 ` Mike McGrath
2007-12-04 22:15 ` Matt Mackall
2007-12-04 22:23 ` Mike McGrath
2007-12-04 22:33 ` Matt Mackall
2007-12-05 14:26 ` Mike McGrath
2007-12-05 14:49 ` Theodore Tso
2007-12-08 7:38 ` Jon Masters
2007-12-08 17:32 ` Theodore Tso
2007-12-08 17:33 ` Mike McGrath
2007-12-08 17:49 ` Theodore Tso
2007-12-08 17:54 ` Jon Masters
2007-12-08 18:15 ` Matt Mackall
2007-12-08 18:24 ` Theodore Tso
2007-12-08 19:36 ` entropy gathering (was Re: Why does reading from /dev/urandom deplete entropy so much?) Jeff Garzik
2007-12-08 19:53 ` Matt Mackall
2007-12-08 20:04 ` Jeff Garzik
2007-12-08 20:19 ` Matt Mackall
2007-12-08 21:07 ` Willy Tarreau
2007-12-08 20:31 ` Theodore Tso
2007-12-08 20:47 ` Jeff Garzik
2007-12-08 20:42 ` Willy Tarreau
2007-12-08 23:47 ` Theodore Tso
2007-12-09 1:07 ` Jon Masters
2007-12-08 18:31 ` Why does reading from /dev/urandom deplete entropy so much? Jeff Garzik
2007-12-08 20:26 ` David Schwartz
2007-12-08 17:43 ` Matt Mackall
2007-12-08 17:47 ` Jon Masters
2007-12-08 18:05 ` Theodore Tso
2007-12-08 17:45 ` Jon Masters
2007-12-10 16:37 ` Pavel Machek
2007-12-04 18:01 ` Matt Mackall
2007-12-06 20:08 ` Bill Davidsen
2007-12-05 12:23 ` Marc Haber
2007-12-05 12:29 ` Marc Haber
2007-12-05 13:33 ` Theodore Tso
2007-12-05 15:10 ` Marc Haber
2007-12-06 19:32 ` Bill Davidsen
2007-12-08 22:03 ` Adrian Bunk
2007-12-08 22:10 ` Ismail Dönmez
2007-12-08 23:46 ` Theodore Tso
2007-12-09 5:21 ` Willy Tarreau
2007-12-09 6:52 ` Jon Masters
2007-12-09 6:21 ` Ismail Dönmez
2007-12-09 12:31 ` Theodore Tso
2007-12-09 14:06 ` Ismail Dönmez
2007-12-11 15:42 ` Bill Davidsen
2007-12-20 22:27 ` Marc Haber
2007-12-26 18:27 ` Phillip Susi
2007-12-04 18:49 ` Russ Dill
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