> After subtracting the timer interrupts, we get an average of over
> nine bits added on each /dev/psaux interrupt to the /dev/random pool.
> I don't think that there is that much entropy involved to justify this
> high value.
How many bits would you propose? Remember you've got several sources of
randomness here:
1) time between mouse events (in processor cycles, usually)
2) x delta
3) y delta
4) button status
Nine bits doesn't seem all that unreasonable to me. And if you care, why
not distill it further. The techniques used to make very random numbers
out of partially random numbers are well known.
Speaking personally, I would like to see much more analysis of the sources
of mouse randomness and the number of bits you think we can "reasonably"
extract from these before you start throwing stones. Note that the kernel
sources are open, so all the algorithms are in plain view. In particular,
the algorithm used to calculate how many bits of 'true' randomness we're
getting for each parcel of information added to the pot is in
linux/drivers/char/random.c, and takes into account first and second order
deltas to more accurately respond to how 'random' your input source
currently is. I suspect during your test you were tossing the mouse
around quite randomly, leading to a greater amount of entropy added to the
pot than if you observed more 'natural' conditions with smaller mouse
movements.
--s
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