On Tue, Jun 26, 2007 at 04:12:26PM +0200, Michael Buesch wrote:
> On Tuesday 26 June 2007 05:13:41 Matt Mackall wrote:
> > On Sun, Jun 24, 2007 at 03:55:22PM +0200, Michael Buesch wrote:
> > > This adds quality categories for hardware random number generators.
> > >
> > ...
> > > +
> > > +/**
> > > + * enum hwrng_quality - Quality identifier for RNG hardware
> > > + * @HWRNG_QUAL_HIGH: High quality RNG. Higher quality than
> > > + * what is found on the usual PC mainboards.
> > > + * Use that for special dedicated RNG
> > > + * extension boards.
> > > + * @HWRNG_QUAL_NORMAL: PC-onboard-RNG devices.
> > > + * @HWRNG_QUAL_LOW: Low quality RNG devices. Use this for
> > > + * devices which gather the entropy from possibly
> > > + * bad sources, like the network.
> > > + * @HWRNG_QUAL_PSEUDO: Pseudo RNG device. Use this for devices
> > > + * which are not RNG devices by definition, but
> > > + * could be used as such. For example various
> > > + * hardware sensors, like a motion sensor.
> > > + */
> >
> > I don't think these definitions are very useful.
> ...
>
> No wait. You are missing the whole point of this
> quality category.
> The whole point of it is to prevent defaulting to a bad RNG, if
> there's a bad and a good one in a machine.
> Well, what's bad.
> It's easy. HWRNGs like the one in bcm43xx are bad.
> It's proprietary and nobody knows what it does (I guess
> it gathers the entropy from the network or something
> and hashes that in hardware).
> So such a device would be QUAL_LOW.
If it's gathering its entropy from the network, it is not a QUAL_LOW
RNG because it is not a hardware random number generator at all!
Such a device is QUAL_PSEUDO or QUAL_UNKNOWN. If it's known or
suspected to be bogus, it should be so marked.
Once you've merged your LOW class with PSEUDO, you're left with a
meaningless, unquantifiable distinction between NORMAL and HIGH.
So we're down to one bit distinguishing real RNGs from pseudo RNGs.
--
Mathematics is the supreme nostalgia of our time.
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