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. > > > > This should really be explained in the help text. > > > > I assume that after 10 seconds of moving mouse, user is safe even when > > rdrand is backoored? > > 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. > > > (Plus, I'd say this should be kernel command line option, not config > > option...?) > > 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 -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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