linux-kernel - Re: [PATCH v6 0/5] /dev/random

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Date:	Wed, 17 Aug 2016 07:21:19 +0200
From:	Stephan Mueller <smueller@...onox.de>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>
Cc:	herbert@...dor.apana.org.au, Ted Tso <tytso@....edu>,
	sandyinchina@...il.com, Jason Cooper <cryptography@...edaemon.net>,
	John Denker <jsd@...n.com>, Joe Perches <joe@...ches.com>,
	Pavel Machek <pavel@....cz>,
	George Spelvin <linux@...izon.com>,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 0/5] /dev/random - a new approach

Am Dienstag, 16. August 2016, 15:28:45 CEST schrieb H. Peter Anvin:

Hi Peter,

> > 
> > There are two motivations for that:
> > 
> > - the current /dev/random is compliant to NTG.1 from AIS 20/31 which
> > requires (in brief words) that entropy comes from auditible noise
> > sources. Currently in my LRNG only RDRAND is a fast noise source which is
> > not auditible (and it is designed to cause a VM exit making it even
> > harder to assess it). To make the LRNG to comply with NTG.1, RDRAND can
> > provide entropy but must not become the sole entropy provider which is
> > the case now with that change.
> > 
> > - the current /dev/random implementation follows the same concept with the
> > exception of 3.15 and 3.16 where RDRAND was not rate-limited. In later
> > versions, this was changed.
> 
> I'm not saying it should be *sole*.  I am questioning the value in
> limiting it, as it seems to me that it could only ever produce a worse
> result.

It is not about the limiting of the data. It is all about the entropy estimate 
for those noise sources and how they affect the entropy estimator behind /dev/
random. If that fast noise source injects large amount of data but does not 
increase the entropy estimator, it is of no concern.

Ciao
Stephan