From: Stephan Mueller Subject: Re: [PATCH v6 0/5] /dev/random - a new approach Date: Wed, 17 Aug 2016 07:21:19 +0200 Message-ID: <1951611.sxsEZ06mGE@tauon.atsec.com> References: <4723196.TTQvcXsLCG@positron.chronox.de> <2672856.NsbgmUcCJx@tauon.atsec.com> <2f43d23f-5fbe-9653-fc1c-489db1c7bde4@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Cc: herbert@gondor.apana.org.au, Ted Tso , sandyinchina@gmail.com, Jason Cooper , John Denker , Joe Perches , Pavel Machek , George Spelvin , linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org To: "H. Peter Anvin" Return-path: Received: from mail.eperm.de ([89.247.134.16]:36636 "EHLO mail.eperm.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750853AbcHQFVX (ORCPT ); Wed, 17 Aug 2016 01:21:23 -0400 In-Reply-To: <2f43d23f-5fbe-9653-fc1c-489db1c7bde4@linux.intel.com> Sender: linux-crypto-owner@vger.kernel.org List-ID: 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