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SubjectRe: [PATCH] add_mouse_randomness
On Fri, Sep 05, 2003 at 11:16:05AM +0200, Andries.Brouwer@cwi.nl wrote:
> From oxymoron@waste.org Fri Sep 5 07:01:30 2003
> From: Matt Mackall <mpm@selenic.com>
>
> > Today:
> > Every keypress and every key release causes two calls of
> > add_mouse_randomness and one call of add_keyboard_randomness.
> > Key repeat causes lots of calls of add_mouse_randomness.
> >
> > The random driver contains a mechanism (delta, delta2, delta3)
> > for estimating the amount of entropy in a stream of moments in
> > time. But the fact that every event causes two calls, very
> > quickly after each other, poisons this mechanism, and makes us
> > overestimate.
>
> The real problem is that the deltas are calculated from gigahertz
> cycle counters, but yes, we're calling too frequently and blowing away
> useful history. I've experimented with making the deltas per-source as
> well.
>
> I wouldnt know what is wrong with using gigahertz cycle counters.
> The deltas are already per-source.

Actually, they're only per-class. So if you have multiple mice,
keyboards, drives, etc., they interfere with each other's deltas and
increase the entropy estimates overall.

--
Matt Mackall : http://www.selenic.com : of or relating to the moon
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