From: "H. Peter Anvin" <hpa@zytor.com>
To: Paul Mackerras <paulus@samba.org>
Cc: Stanimir Varbanov <svarbanov@mm-sol.com>,
Theodore Ts'o <tytso@mit.edu>,
Rob Herring <rob.herring@calxeda.com>,
Pawel Moll <pawel.moll@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Stephen Warren <swarren@wwwdotorg.org>,
Ian Campbell <ijc+devicetree@hellion.org.uk>,
Matt Mackall <mpm@selenic.com>,
Herbert Xu <herbert@gondor.hengli.com.au>,
linux-kernel@vger.kernel.org, Rob Landley <rob@landley.net>,
devicetree@vger.kernel.org, linux-doc@vger.kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-arm-msm@vger.kernel.org
Subject: Re: [PATCH 0/2] Add support for Qualcomm's PRNG
Date: Thu, 10 Oct 2013 08:08:25 -0700 [thread overview]
Message-ID: <5256C2E9.4010704@zytor.com> (raw)
In-Reply-To: <20131010104140.GE9906@iris.ozlabs.ibm.com>
On 10/10/2013 03:41 AM, Paul Mackerras wrote:
> On Wed, Oct 09, 2013 at 08:07:35AM -0700, H. Peter Anvin wrote:
>
>> consider the PowerPC random number generator[1]) and
>
> [snip]
>
>> [1] which has a known first-order bias which they "correct" for by
>> XORing two datums together in a very simple data reduction step.
>
> 65 actually, not two.
>
>> However, if their random source has bias it is extremely likely it also
>> has nonzero correlations, which require stronger reductions. It would
>
> The correlations are essentially zero, by design, and experiment
> confirms it. Did you see my mail on the kvm list where I explained
> how it works?
>
No, sorry... I got a bit of detached discussion as part of benh talking
about KVM and randomness (for the record, I'm all for better randomness
on all platforms.)
Either way, XORing samples is a pretty inefficient (both in terms of
anticorrelation and in terms of entropy efficiency) form of data
reduction/conditioning. It would still be better to feed the output
into the pool with a 65x derating.
-hpa
next prev parent reply other threads:[~2013-10-10 15:10 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-03 14:52 [PATCH 0/2] Add support for Qualcomm's PRNG Stanimir Varbanov
2013-10-03 14:52 ` Stanimir Varbanov
2013-10-03 14:52 ` [PATCH 1/2] ARM: DT: msm: Add Qualcomm's PRNG driver binding document Stanimir Varbanov
2013-10-03 14:52 ` Stanimir Varbanov
2013-10-03 14:52 ` [PATCH 2/2] hwrng: msm: Add PRNG support for MSM SoC's Stanimir Varbanov
2013-10-03 14:52 ` Stanimir Varbanov
2013-10-03 19:25 ` Stephen Boyd
2013-10-03 19:25 ` Stephen Boyd
2013-10-04 16:31 ` Stanimir Varbanov
2013-10-04 16:31 ` Stanimir Varbanov
2013-10-04 16:37 ` Stephen Boyd
2013-10-04 16:37 ` Stephen Boyd
2013-10-09 8:23 ` Stanimir Varbanov
2013-10-09 8:23 ` Stanimir Varbanov
[not found] ` <1380811955-18085-1-git-send-email-svarbanov-NEYub+7Iv8PQT0dZR+AlfA@public.gmane.org>
2013-10-03 16:51 ` [PATCH 0/2] Add support for Qualcomm's PRNG Theodore Ts'o
2013-10-03 16:51 ` Theodore Ts'o
[not found] ` <20131003165130.GA11974-AKGzg7BKzIDYtjvyW6yDsg@public.gmane.org>
2013-10-04 16:23 ` Stanimir Varbanov
2013-10-04 16:23 ` Stanimir Varbanov
[not found] ` <524EEB96.6040707-NEYub+7Iv8PQT0dZR+AlfA@public.gmane.org>
2013-10-04 18:10 ` Theodore Ts'o
2013-10-04 18:10 ` Theodore Ts'o
2013-10-09 14:46 ` Stanimir Varbanov
2013-10-09 15:07 ` H. Peter Anvin
2013-10-09 16:03 ` Theodore Ts'o
2013-10-09 16:24 ` H. Peter Anvin
2013-10-10 7:46 ` rngd (was: [PATCH 0/2] Add support for Qualcomm's PRNG) Clemens Ladisch
2013-10-10 15:08 ` rngd H. Peter Anvin
2013-10-10 19:48 ` rngd Theodore Ts'o
2013-10-10 10:41 ` [PATCH 0/2] Add support for Qualcomm's PRNG Paul Mackerras
2013-10-10 15:08 ` H. Peter Anvin [this message]
2013-10-10 13:47 ` Stanimir Varbanov
2013-10-11 7:05 ` Clemens Ladisch
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