[Beowulf] OT: public random numbers?

Robert G. Brown rgb at phy.duke.edu
Fri Aug 12 11:35:17 PDT 2011

On Fri, 12 Aug 2011, David Mathog wrote:

> Robert G. Brown wrote:
>>  Everybody must be able to obtain it
>>> freely from a web connection.
>>    http://www.random.org/
> Nice site.  They have something that is very close, the pregenerated
> random files, from which a small set of digits may be extracted, and the
> files themselves have MD5 checksums (but are not signed).
> They also support https.  It comes up a little short on criteria 1 (we
> really don't know what is going on behind the scenes) and 6 (it is a
> single site.)

Behind the scenes is documented pretty well on the site, and the guy who
runs it is a human being, you can communicate with him to learn even
more.  I already know him a bit, as he and I have collaborated on
applying dieharder to test random.org datasets -- even "the" random.org
dataset as of some time ago (I have a few hundred MB of random number
from the site in my dieharder directory).  IIRC, the numbers are
generated continuously and fairly slowly by grabbing and filtering and
transforming atmospheric noise.  As a source of entropy, that is
probably excellent if (as noted) slow, but many good sources of entropy
seem to be fairly slow.  He has good reason to think that his numbers
are theoretically "true random numbers" -- both unpredictable and
flat/decorrelated at all orders, and even though there aren't really
enough of them for my purposes, I've used them as one of the (small)
"gold standard" sources for testing dieharder even as I test them.  For
all practical purposes threefish or aes are truly random as well and
they are a lot faster and easier to use as gold standard generators,

I don't quite understand why the single site restriction is important --
this site has been up for years and I don't expect it to go away soon;
it is quite reliable.  I don't think there is anything secret about how
the numbers are generated, and I'll certify that the numbers it produces
don't make dieharder unhappy.  So 1 is fixable with a bit of effort on
your part; 6 I don't really understand but the guy who runs the site is
clearly willing to construct a custom feed for cash customers, if there
is enough value in whatever it is you are trying to do to pay for
access.  If it's just a lottery, well, lord, I can think of a dozen ways
to make numbers so random that they'd be unimpeachable for any sort of
lottery, both unpredictable and uncorrelated, and they don't any of them
require any significant amount of entropy to get started.

I will add one warning -- "randomness" is a rather stringent
mathematical criterion, and is generally tested against the null
hypothesis.  Amateurs who want to make random number generators out of
supposedly "random" data streams or fancy algorithms almost invariably
fail, sometimes spectacularly so.  There are a half dozen or more
really, really good pseudorandom number generators out there and it is
easy to hotwire them together into an xor-based high entropy stream that
basically never repeats (feeding it a bit of real entropy now and then
as it operates).  I would strongly counsel you against trying to take
e.g. weather data and make something "random" out of it.  Unless you
really know what you are doing, you will probably make something that
isn't at all random and may not even be unpredictable.  Even most
sources of "quantum" randomness (which is at least possibly "truly
random", although I doubt it) aren't flat, so that they carry the
signature of their generation process unless/until you manage to
transform them into something flat (difficult unless you KNOW the
distribution they are producing).  Pseudorandom number generators have
the serious advantage of being amenable to at least some theoretical
analysis (so you can "guarantee" flatness out to some high
dimensionality, say) as well as empirical testing with e.g. dieharder.



> Thanks,
> David Mathog
> mathog at caltech.edu
> Manager, Sequence Analysis Facility, Biology Division, Caltech

Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at phy.duke.edu

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