From: Matt Mackall <mpm@selenic.com>
To: Thiago Galesi <thiagogalesi@gmail.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH 7/14] random: Remove SA_SAMPLE_RANDOM from network drivers
Date: Sun, 7 May 2006 11:00:14 -0500 [thread overview]
Message-ID: <20060507160013.GM15445@waste.org> (raw)
In-Reply-To: <82ecf08e0605070613o7b217a2bw4c71c3a8c33bed28@mail.gmail.com>
On Sun, May 07, 2006 at 10:13:50AM -0300, Thiago Galesi wrote:
> >Sure.
> >
> >First, since the existence of /dev/random's entropy accounting scheme
> >is predicated on the assumption that we can break the hash function at
> >will, I'll replace SHA1 with, oh, say, CRC-16. This'll be illustrative
> >until someone has a nice preimage attack against SHA1.
> >
> >Then I'll run my test on one of the various arches where HZ=~100 and
> >we don't have a TSC. Like Sparc?
> >
> >Now all the inputs are easily predictable from anywhere with <10ms
> >ping, with the occassional need to guess between a pair of timer
> >ticks. And since I can calculate preimages of CRC-16, I can now deduce
> >the state of the pool if I can watch some subset of its output, say
> >https session keys I request. And then I can start guessing future
> >outputs and breaking into other people's https sessions.
> >
> >The point of /dev/random is to -survive- SHA1 being broken by never
> >giving out more secrets than we take in.
>
> OK, here goes...
>
> 1 - by eliminating feeding enthopy from network cards you are
Keep up, folks, I dropped that position in the very first round of replies.
> 2 - some platforms have much better enthropy sources than ethernet (or
> user input), just think hardware rngs, or even the sound card rng
> thing mentioned above
Point?
> 3 - as people said, your example (CRC-16 on specific platfoms) is
> (IMHO) an exxageration.
Yes, CRC-16 was a rhetorical device. MD4 would not have been. HZ=100
is not an exaggeration. Odds are pretty good you have such a Linux box
in the form of a router or such already. This completely invalidates
all the arguments about the hardware making the timing too
unpredictable as it does so on a timescale of microseconds or less.
--
Mathematics is the supreme nostalgia of our time.
next prev parent reply other threads:[~2006-05-07 16:05 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-05-05 16:42 [PATCH 1/14] random: Remove SA_SAMPLE_RANDOM from floppy driver Matt Mackall
2006-05-05 16:42 ` [PATCH 6/14] random: Remove redundant SA_SAMPLE_RANDOM from touchscreen drivers Matt Mackall
2006-05-05 16:42 ` [PATCH 4/14] random: Change cpqarray to use add_disk_randomness Matt Mackall
2006-05-05 16:42 ` [PATCH 2/14] random: Remove redundant SA_SAMPLE_RANDOM from NinjaSCSI Matt Mackall
2006-05-05 16:42 ` [PATCH 3/14] random: Make CCISS use add_disk_randomness Matt Mackall
2006-05-05 16:42 ` [PATCH 5/14] random: Remove bogus SA_SAMPLE_RANDOM from at91 compact flash driver Matt Mackall
2006-05-05 16:42 ` [PATCH 8/14] random: Remove SA_SAMPLE_RANDOM from USB gadget drivers Matt Mackall
2006-05-06 11:07 ` Denis Vlasenko
2006-05-06 18:16 ` David Brownell
2006-05-06 18:31 ` Matt Mackall
2006-05-05 16:42 ` [PATCH 7/14] random: Remove SA_SAMPLE_RANDOM from network drivers Matt Mackall
2006-05-05 17:13 ` Kyle Moffett
2006-05-05 17:24 ` Matt Mackall
2006-05-05 19:11 ` Theodore Tso
2006-05-05 20:30 ` Stephen Hemminger
2006-05-05 20:34 ` Matt Mackall
2006-05-06 11:55 ` Theodore Tso
2006-05-06 16:48 ` Matt Mackall
2006-05-06 17:29 ` Bernd Eckenfels
2006-05-06 18:05 ` Theodore Tso
2006-05-06 20:33 ` Matt Mackall
2006-05-07 0:17 ` David S. Miller
2006-05-07 1:22 ` Theodore Tso
2006-05-07 5:07 ` Matt Mackall
2006-05-08 21:58 ` Sami Farin
2006-05-24 22:47 ` Marcin Dalecki
2006-05-25 0:08 ` Theodore Tso
2006-05-31 19:29 ` Bill Davidsen
2006-05-07 0:08 ` David S. Miller
2006-05-07 4:59 ` Matt Mackall
2006-05-07 5:46 ` David S. Miller
2006-05-07 16:31 ` Matt Mackall
2006-05-07 13:13 ` Thiago Galesi
2006-05-07 16:00 ` Matt Mackall [this message]
2006-05-07 17:00 ` Thiago Galesi
2006-05-08 0:13 ` Theodore Tso
2006-05-08 2:55 ` Matt Mackall
2006-05-08 6:26 ` Pavel Machek
2006-05-08 7:07 ` David S. Miller
2006-05-08 14:05 ` Matt Mackall
2006-05-08 17:21 ` Pavel Machek
2006-05-08 17:27 ` Matt Mackall
2006-05-09 11:23 ` Pavel Machek
2006-05-11 10:05 ` Ph. Marek
2006-05-24 22:35 ` Marcin Dalecki
2006-05-05 21:10 ` David S. Miller
2006-05-05 23:03 ` Matt Mackall
2006-05-05 23:19 ` David S. Miller
2006-05-06 14:08 ` Folkert van Heusden
2006-05-06 15:19 ` Lee Revell
2006-05-07 10:35 ` Folkert van Heusden
2006-05-07 16:33 ` Matt Mackall
2006-05-05 16:42 ` [PATCH 9/14] random: Remove SA_SAMPLE_RANDOM from i2c drivers Matt Mackall
2006-05-05 16:42 ` [PATCH 10/14] random: Remove bogus SA_SAMPLE_RANDOM from mpc52xx serial driver Matt Mackall
2006-05-05 16:42 ` [PATCH 11/14] random: Remove UML usage of SA_SAMPLE_RANDOM Matt Mackall
2006-05-05 16:42 ` [PATCH 13/14] random: Remove SA_SAMPLE_RANDOM from IRQ fastpath Matt Mackall
2006-05-05 16:42 ` [PATCH 12/14] random: Remove not very useful SA_SAMPLE_RANDOM from lubbock Matt Mackall
2006-05-05 16:42 ` [PATCH 14/14] random: Remove add_interrupt_randomness Matt Mackall
2006-05-08 7:38 [PATCH 7/14] random: Remove SA_SAMPLE_RANDOM from network drivers linux
2006-05-12 6:09 ` linux
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