Date: Thu, 23 Jul 2015 22:42:41 +0100 From: Mark R V Murray <markm@FreeBSD.org> To: Alexey Dokuchaev <danfe@FreeBSD.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers <src-committers@freebsd.org> Subject: Re: svn commit: r284959 - in head: . share/man/man4 share/man/man9 sys/conf sys/dev/glxsb sys/dev/hifn sys/dev/random sys/dev/rndtest sys/dev/safe sys/dev/syscons sys/dev/ubsec sys/dev/virtio/random sy... Message-ID: <B592C9B9-DB00-43EB-A0EC-31C098C7B885@FreeBSD.org> In-Reply-To: <20150723173016.GA86452@FreeBSD.org> References: <201506301700.t5UH0jPq001498@svn.freebsd.org> <alpine.BSF.2.20.1507221138360.1071@desktop> <FFAED695-145A-45F5-988D-B843EF5F544B@FreeBSD.org> <alpine.BSF.2.20.1507221249120.1071@desktop> <FFFB06D7-164B-40B3-AFC3-A6630BCF074E@bsdimp.com> <E20B169F-4C8A-4D11-9853-5C2EFC116450@FreeBSD.org> <F54A96A8-D9AD-409A-814F-538B6AD3CD50@yahoo.com> <20150723173016.GA86452@FreeBSD.org>
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> On 23 Jul 2015, at 18:30, Alexey Dokuchaev <danfe@FreeBSD.org> wrote: >=20 > [ Guys, please teach your MUA to wrap messages over 72-76 boundary and = trim > excessive/irrelevant quoting, thank you. ] Oops sorry! > So far it looks like this to me (having read no papers): >=20 > 1) Fortuna attempts to get the most entropy from all available = sources, > trusting none of them. (Which is good.) Accurate. > 2) Some of them might/will cause unwanted performance loss under = certain > circumstances, which becomes a show-stopper (finite number of clock = cycles > available, etc.) for some use cases. Again accurate. > If Fortuna is so flexible, why can't some of its sources be = conditionally > disabled (kernel option/boot.conf/systct) or down-weighted through = some > more sophisticated, self-adjusting configuration technique during = runtime? This is already present, but some if these checks, while very cheap, are still too expensive in very high-performance areas of the code. > How dynamic it is? Mark, is there a (algorithmically?) reliable way = to > tell how many bits of "good" entropy is being added to the pool, and = then > tune the harvesting strategy accordingly? No. Not an absolute =E2=80=9Cno=E2=80=9D, but The Yarrow algorithm = required this, and it was never implemented satisfactorily by anyone due to its difficulty. Yarrow is now no longer supported by its authors due to this, amongst other problems. > Is there some sort of restricted, private API to get a clue about = current > entropy status? Sort of. By turning on the RANDOM_DEBUG option, Fortuna will = periodically print out the =E2=80=9Cmessage lengths=E2=80=9D of all 32 accumulation = pools. These are very vaguely indicative of the accumulated entropy. Pool[0] is used for reseeding; the rest are there for my interest and will be removed at = some point. M --=20 Mark R V Murray
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