Re: Entropy from disks

[Oliver Xymoron <oxymoron@waste.org>]

On Tue, Nov 05, 2002 at 03:55:57PM -0800, David Schwartz wrote:
> 
> On Tue, 29 Oct 2002 13:02:39 -0500, Chris Friesen wrote:
> >Oliver Xymoron wrote:
> 
> >I'm not an expert in this field, so bear with me if I make any blunders
> >obvious to one trained in information theory.
> 
> >>The current Linux PRNG is playing fast and loose here, adding entropy
> >>based on the resolution of the TSC, while the physical turbulence
> >>processes that actually produce entropy are happening at a scale of
> >>seconds. On a GHz processor, if it takes 4 microseconds to return a
> >>disk result from on-disk cache, /dev/random will get a 12-bit credit.
> 
> >In the paper the accuracy of measurement is 1ms.  Current hardware has
> >tsc precision of nanoseconds, or about 6 orders of magnitude more
> >accuracy.  Doesn't this mean that we can pump in many more bits into the
> >algorithm and get out many more than the 100bits/min that the setup in
> >the paper acheives?
> 
> 	In theory, if there's any real physical randomness in a timing source, the 
> more accuracy you measure the timing to, the more bits you get.

Not if the timing source is clocked at a substantially slower speed
than the measurement clock and is phase locked. Which is the case.

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