Re: [PATCH] add_mouse_randomness

[Matt Mackall <mpm@selenic.com>]

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