From: Pavel Machek Subject: Re: [PATCH] random: add a config option to trust the CPU's hwrng Date: Sun, 5 Aug 2018 11:44:32 +0200 Message-ID: <20180805094432.GA22948@amd> References: <20180718014344.1309-1-tytso@mit.edu> <37046662f2b38f98854abfa1b5868a27c3fa0888.camel@opteya.com> <20180718142625.GA5942@thunk.org> <20180804215209.GA3201@localhost> <20180805002514.GF4461@thunk.org> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="qDbXVdCdHGoSgWSk" To: "Theodore Y. Ts'o" , Yann Droneaud , linux-crypto@vger.kernel.org, Linux Kernel Developers List , labbott@redhat.com Return-path: Content-Disposition: inline In-Reply-To: <20180805002514.GF4461@thunk.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org --qDbXVdCdHGoSgWSk Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sat 2018-08-04 20:25:14, Theodore Y. Ts'o wrote: > On Sat, Aug 04, 2018 at 11:52:10PM +0200, Pavel Machek wrote: > > > However, enabling config option means that the CRNG will be > > > initialized with potentially information available to the CPU > > > manufacturer and/or Nation States, and this persists *after* > > > initialization / early boot. So to say, "we're perfectly safe after > > > we leave initialization / early boot" is not true. > >=20 > > This should really be explained in the help text. > >=20 > > I assume that after 10 seconds of moving mouse, user is safe even when > > rdrand is backoored? >=20 > You'll hate this answer, but "it depends". Suppose someone is using > an init script which generates ssh keys upon first boot if they are > missing. If this is the case, *and* RDRAND is backdoored, then the > keys will be generated in such a way that they *might* be succeptible > to being guessed by a nation state. Moving your mouse around for 1000 > or 10,000 seconds won't help if the host's ssh keys has already been > generated. Yep, understood, but after moving the mouse, /dev/random & /dev/urandom can be trusted afaict. > Depending on your hardware, no mouse motion might be necessary at all. > On my laptop (a Dell XPS 13 model 9370) using an dm-crypt protected > root disk, and running a Debian testing userspace, with a 4.18-rc6 > based kernel, the "CRNG is initialized" message is printed *before* > the root file system is mounted. Entropy is easy to gather on any laptop. cat /dev/sda > /dev/null :-). > On other systems, where the hardware does not issue as many > interrupts, the mouse motion might be extremely important in order to > get the "CRNG is initialized" message. >=20 > > (Plus, I'd say this should be kernel command line option, not config > > option...?) >=20 > Agreed, there should be a command line option as well. I just haven't > gotten around to it yet, and in the meantime, having a config option > is better than nothing. Patches gratefully accepted... :-) Well, this was RFC :-). I actually don't think config option is good idea. Command line option is enough. Pavel --=20 (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo= g.html --qDbXVdCdHGoSgWSk Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iEYEARECAAYFAltmxwAACgkQMOfwapXb+vIjlgCgnqUZ7Qv6cY/V9TqL13r+UIEB KMoAn1XlG4RzYJsKqFZOOgBvVwiKU6Aq =/iEp -----END PGP SIGNATURE----- --qDbXVdCdHGoSgWSk--