Date: Sat, 22 Jul 2000 22:51:53 -0400 From: "Jeroen C. van Gelderen" <jeroen@vangelderen.org> To: Kris Kennaway <kris@FreeBSD.org> Cc: arch@freebsd.org Subject: Re: Quantifying entropy Message-ID: <397A5DC9.91DAAD8C@vangelderen.org> References: <Pine.BSF.4.21.0007211831540.68809-200000@freefall.freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
Kris Kennaway wrote:
>
> I've been playing around with measuring the entropy of sound card
> microphone inputs when they have no microphone attached (i.e. intrinsic
> noise in the sound card). I've tested on two systems: my SB16 and a
> CS423x, and found quite different results:
>
> My SB16 in 8bit mode has about 0.06 bits of entropy per sample
> The CS423x has about 5.8 bits per sample (!).
>
> SB16 in 16bit mode recording seems to be broken at the moment.
> CS423x in 16bit mode has about 8.5 bits per sample.
Kewl!
> The noise spectra look mostly gaussian (except for the SB16 which gives a
> weird quantized spectrum of only 5 possible return values and a strongly
> correlated output pattern ;-, though I've not plotted them, but only
> inspected the frequency distribution table. I haven't performed any
> statistical tests for signal correlation beyond calculating the Shannon
> entropy in the probability distribution. I'd be interested to see results
> from other people (test program attached)
Could you make a couple of megabytes of you raw samples
available? I don't have a soundcard at hand but I do
have the FIPS-140 tests and a bunch of others.
> What this seems to suggest is that in the wider picture of gathering
> entropy, the amount of noise in a given (logical) source is going to be
> very hardware and system-specific, and trying to assign a fixed weight to
> it may either grossly overestimate or underestimate the amount of true
> entropy in the sample.
The Yarrow authors proposed various methods of dynamically
estimating the entropy. One of those was to simply feed the
data trough gzip and see how much it compresses. Halve the
number of compressed bits and would have a pretty conservative
estimate.
Cheers,
Jeroen
--
Jeroen C. van Gelderen o _ _ _
jeroen@vangelderen.org _o /\_ _ \\o (_)\__/o (_)
_< \_ _>(_) (_)/<_ \_| \ _|/' \/
(_)>(_) (_) (_) (_) (_)' _\o_
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-arch" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?397A5DC9.91DAAD8C>