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'[OT] random numbers'
2007\10\05@013849 by Al Shinn

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Is the number of seconds (say XXXX0.00 to XXXX9.99 sec)  since midnight
a truly random number?  You could only use it once in awhile of course.
maybe use NOW to seed a generator?     IANAM!! (mathematician) so
forgive if this is trivial.

Speaking of random, (as in random fluctuation of the vacuum something or
other), if all of the mass of the universe started in an infinitesimal
volume (a point?) as proposed by the big bang (I think that's what the
theory says), then wouldn't that have been The Mother Of All Black
Holes? So, how did we get out? Or did we?   I always pay attention to
related matters and have never seen this mentioned.
IANAC!!! (cosmologist) but my brother in law is - he seems to hate this
question and has never answered it (I've asked twice). Perhaps it annoys
him because it is a stupid question??

--

Looking forward,
Al Shinn


2007\10\05@030949 by Tony Smith

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> Is the number of seconds (say XXXX0.00 to XXXX9.99 sec)  
> since midnight a truly random number?  You could only use it
> once in awhile of course.
> maybe use NOW to seed a generator?     IANAM!! (mathematician) so
> forgive if this is trivial.


Random is never trivial.  The short answer to you question is no & maybe.

Two problems with time of day; it's a known sequence, so I can guess what
the next number is going to be, and I'll get the same number at the same
time each day, ie at midnight it's always zero.

You may be happy with this, of course.

There's a number of bit-twiddling routines for use on PICs, they'll generate
a psuedo-random sequence that may be good enough.  Instead of generating
1,2,3,4,5,6,etc you get 4,2,3,6,1,5.  Unfortunately after a while the
sequence will repeat.  Ok for dice rolling, no good for Lotto.

Seeding improves things, the usual trick is to rely on some outside
influence.  You could always have the sequence running, and when a button is
pushed output the current number in the sequence.  (Its flaw is that if you
power up the chip and instantly hit the button, you'll always get the very
first number in the series).

Other ways to do this is to detect some 'noise' from the real world that
causes the counter to increment thru the series in a hopefully random
matter, or to make the noise the actual number.  Say you had a light sensor;
a bright light trips the counter, or is a 'big' number.  Low light does
nothing to the counter (or increments it slowly, bright = fast), or is a
'small' number. Needless to say, these have their problems too.  Ok for
Government work, natually.

There's a website that serves up random numbers out there somewhere.

Tony

2007\10\05@033604 by wouter van ooijen

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> Is the number of seconds (say XXXX0.00 to XXXX9.99 sec)  
> since midnight a truly random number?

If you sample it at a random moment it is certainly random :)

The trouble about random is that - like most scientific notions - it has
no qualification test, only disqualification tests. And for randomness
even those disqalification tests are statistical, the type of answer
they give is "the chance that this sequence was truly random according
to this test is (only) 15%". In most practical situations the question
is whether a sequence is sufficiently random for a  certain purpose.
That's an engineering question (or even a management question!), not a
scientific question.

> So, how did we get out?

I guess there was no energy crisis way back then.

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu



2007\10\05@082145 by David VanHorn

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> There's a website that serves up random numbers out there somewhere.

Lavarand!  :)

http://www.lavarnd.org/

2007\10\05@093437 by Funny NYPD

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If you are using a PIC, a high-speed timer might be a simple good bet. You can even write an algorithm to take advantage the timer values, which will make a better pseudo-random number.

Funny



----- Original Message ----
From: David VanHorn <spam_OUTmicrobrixTakeThisOuTspamgmail.com>
To: Microcontroller discussion list - Public. <.....piclistKILLspamspam@spam@mit.edu>
Sent: Friday, October 5, 2007 8:21:16 AM
Subject: Re: [OT] random numbers


> There's a website that serves up random numbers out there somewhere.

Lavarand!  :)

http://www.lavarnd.org/

2007\10\05@142312 by Martin Klingensmith

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There are LFSR routines for PICs out there as well.
--
Martin K

Funny NYPD wrote:
{Quote hidden}

2007\10\05@175434 by Jinx

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> If you are using a PIC, a high-speed timer might be a simple

Measuring WDT period at high resolution should be a reasonably
variable seed if you need to keep PRNG generation internal. You
could do (maybe not so silly) things such as occassionally turn on a
warming resistor that heats the PIC, thereby changing WDT, it
being RC-based and variable with temperature. The main point is
having an external or analogue component influencing the digital

2007\10\05@181517 by Brendan Gillatt

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-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Al Shinn wrote:
{Quote hidden}

One of they guys at sparkfun created random numbers from noise picked up
on the A/D channels of a micro. See
www.sparkfun.com/commerce/present.php?p=Sinister7
if anybody's interested.

- --
Brendan Gillatt
brendan {at} brendangillatt {dot} co {dot} uk
http://www.brendangillatt.co.uk
PGP Key: pgp.mit.edu:11371/pks/lookup?op=get&search=0xBACD7433
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2007\10\05@183641 by David VanHorn

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On 10/5/07, Funny NYPD <EraseMEfunnynypdspam_OUTspamTakeThisOuTyahoo.com> wrote:
> If you are using a PIC, a high-speed timer might be a simple good bet. You can even write an algorithm to take advantage the timer values, which will make a better pseudo-random number.

Not even close to random, whichever definition you use.

Radioactive decay events are random.

2007\10\06@011100 by David VanHorn

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On 10/5/07, Martin Klingensmith <martinspamspam_OUTnnytech.net> wrote:
> There are LFSR routines for PICs out there as well.

Yeah, but they do repeat, eventually, and if you know the length, and
seed, then you can work out what's next pretty quickly.   I have a 19
bit implementation for the AVR, which I shift every time through the
main loop, and when I use it, I grab a few bits from here, a few from
there, making it harder to attack that way.

But radioactive decay isn't that hard to get, and if someone can show
how to un-randomize that, they have a Nobel waiting.

2007\10\06@013840 by Herbert Graf

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On Sat, 2007-10-06 at 01:10 -0400, David VanHorn wrote:
> On 10/5/07, Martin Klingensmith <@spam@martinKILLspamspamnnytech.net> wrote:
> > There are LFSR routines for PICs out there as well.
>
> Yeah, but they do repeat, eventually, and if you know the length, and
> seed, then you can work out what's next pretty quickly.   I have a 19
> bit implementation for the AVR, which I shift every time through the
> main loop, and when I use it, I grab a few bits from here, a few from
> there, making it harder to attack that way.

Anybody have any experience using the ADC? I figure just connecting a
resistor divider to an ADC pin, reading the value a few hundred times
and doing something with the least significant bit would perhaps give a
relatively good random number?

TTYL

2007\10\06@034144 by Tony Smith

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> > main loop, and when I use it, I grab a few bits from here,
> a few from
> > there, making it harder to attack that way.
>
> Anybody have any experience using the ADC? I figure just
> connecting a resistor divider to an ADC pin, reading the
> value a few hundred times and doing something with the least
> significant bit would perhaps give a relatively good random number?
>
> TTYL


Ask Intel, they tried that on one of their CPUs a while back.

Apart from that, use a carbon resistor, they're noiser.

Tony

2007\10\06@073456 by Gerhard Fiedler

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David VanHorn wrote:

> On 10/5/07, Funny NYPD <KILLspamfunnynypdKILLspamspamyahoo.com> wrote:
>> If you are using a PIC, a high-speed timer might be a simple good bet.

> Not even close to random, whichever definition you use.

That depends on what you use to trigger the timer reads, no? Like ...

> Radioactive decay events are random.

... when timed with the above high-speed timer? :)

Gerhard

2007\10\06@091359 by Bob Axtell

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David VanHorn wrote:
> On 10/5/07, Funny NYPD <RemoveMEfunnynypdTakeThisOuTspamyahoo.com> wrote:
>  
>> If you are using a PIC, a high-speed timer might be a simple good bet. You can even write an algorithm to take advantage the timer values, which will make a better pseudo-random number.
>>    
>
> Not even close to random, whichever definition you use.
>
> Radioactive decay events are random.
>  
One of the biggest problems casino game makers have is convincing the
various gaming authorities that their game generates random numbers.

Of course, computers CANNOT by definition generate a random number,
its truly impossible.

But some events are very random, such as noise from a "pink diode",
radioactive
decay, and outer space explosive events.

I spent some time doing casino player card networks, and was fascinated
at how
often a slot machine was sent back as defective because it paid off too
often...

--Bob

2007\10\06@093702 by David VanHorn

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> One of they guys at sparkfun created random numbers from noise picked up
> on the A/D channels of a micro. See
> www.sparkfun.com/commerce/present.php?p=Sinister7
> if anybody's interested.


Pretty doubtful that is random as in unpredictable, or random as in
equal probability of any value on the next sample.   But depending on
the task, it might seem random enough.

2007\10\06@141941 by William \Chops\ Westfield

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On Oct 6, 2007, at 6:14 AM, Bob Axtell wrote:

> Of course, computers CANNOT by definition generate a random number,
> its truly impossible.
>
> But some events are very random, such as noise from a "pink diode",
> radioactive decay, and outer space explosive events.

I thought one of the classic "truly random" noise sources was a
reverse-biased semiconductor junction.  It shouldn't be too hard
to put a bunch of those on a CPU chip to make a "true random"
register that could be used for software requiring randomness,
or to assist in generating randomness.  (any high speed counter
is pretty random in its low bits, but even if it's counting
radioactive decays, it gets a lot less random in the high bits
as the sample time gets small enough that they're obviously
"just counting."

BillW

2007\10\06@182950 by Jinx

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> I thought one of the classic "truly random" noise sources was a
> reverse-biased semiconductor junction.  It shouldn't be too hard
> to put a bunch of those on a CPU chip to make a "true random"
> register that could be used for software requiring randomness,
> or to assist in generating randomness

I used this generator + two nested timers in a project for a gaming
machine. It was passed by the NZ Dept Of Internal Affairs as being
random. As Bob A indicated, plain PRGN is not acceptable

http://home.clear.net.nz/pages/joecolquitt/white_noise.html

The eventual output of this circuit is digital to an input pin (ie direct
pulse-counting and timing method) but no reason why the analogue
output of amp1 couldn't be read by an ADC for a similar result

2007\10\06@203719 by Marcel Duchamp

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Jinx wrote:
> home.clear.net.nz/pages/joecolquitt/white_noise.html
>
> The eventual output of this circuit is digital to an input pin (ie direct
> pulse-counting and timing method) but no reason why the analogue
> output of amp1 couldn't be read by an ADC for a similar result
>

I used that exact technique 10 years ago to add noise to a sine wave
made with an MF10 filter circuit. The job needed to simulate doppler
spectrum and the noise added to the sine spread out the bandwidth enough
to look like an actual sensor.  This was for a simulator.

2007\10\06@223255 by David VanHorn

picon face
> > Radioactive decay events are random.
>
> ... when timed with the above high-speed timer? :)

Right but the randomness comes entirely from the decay event.
The timer is just showing the time between events.

2007\10\06@223453 by David VanHorn
picon face
> I thought one of the classic "truly random" noise sources was a
> reverse-biased semiconductor junction.  It shouldn't be too hard
> to put a bunch of those on a CPU chip to make a "true random"
> register that could be used for software requiring randomness,
> or to assist in generating randomness.  (any high speed counter
> is pretty random in its low bits, but even if it's counting
> radioactive decays, it gets a lot less random in the high bits
> as the sample time gets small enough that they're obviously
> "just counting."

Right, but then I can hit it with bursts of RF and influence the noise.
(or voltage, or ESD or...)  If you can make radioactive decay be
anything other than random, you need to go pick up your Nobel..   You
can make it faster, by approacing critical mass, but that's the same
as say dividing all the random numbers by 2, they are still random.

2007\10\07@020836 by Jinx

face picon face

> Right but the randomness comes entirely from the decay event
> The timer is just showing the time between events.

I don't think I'd bother personally, but a smoke alarm would be a
radioactive source not too hard to get hold of. Although I can't
say I've ever seen a scrapped one

http://home.howstuffworks.com/smoke3.htm



2007\10\07@145508 by Al Shinn

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There's something that bothers me about radioactive decay being random.
A given chunk of radioactive material will trigger a detector at some
average rate and the time between events will seemingly form something
like a gausian around that rate (I don't know if it would be a
symmetrical gausian, in fact I doubt it). For instance, I was observing
a piece of uranium glass with a geiger counter and got something like 1
count per second. So, a list of the time between each count (lets count
to three decimals) will peak around 1 second and there will be very very
few periods of 000 or even .010 sec, lots more of .500 sec and 1.5 sec,
way more 1.000 sec, and  very few of 10.000 sec (though perhaps more
than 0.000 sec)   I would see many more counts at 2.000 then 0.000sec
(hence the asymmetry) This doesn't seem completely random to me.

Now, if one ran a 100k cps clock and counted only the last four
decimals, then I would expect no such "bias" i.e. equal chance of
xx.xx0000sec as xx.xx9999sec as xx.xx5000sec

So, what would be the names of the two different sorts of randomness?
I don't think that you would want the first example as a random number
generator if you were building a slot machine.

I am sure you would see the same sort of "peaky-ness" with counting the
number of decays per second with a fast source, but somehow it "feels"
like the gausian may be more symmetrical.

I'll bet a doughnut that I am somehow showing a great bit of ignorance
here  :-)  .

So, how would one build a radio decay based random number generator
without the fast clock and counter - to save power? Perhaps generate a
voltage like a survey meter does, but that will have the "peaky-ness"
centered at a function of the average rate. I guess one could use just
the last few decimals of the AtoD?

Well, I'll be double da#$d, I just this minute went out to my car to get
my Geiger counter and found out why the car alarm went off last night -
someone stole my Geiger counter!!! Bummer I really liked it - it will be
expensive to replace!!
--

Looking forward,
Al Shinn



2007\10\07@153013 by wouter van ooijen

face picon face
> There's something that bothers me about radioactive decay
> being random.

The fact that you can use it to deliver something that is not random
does not disqualify it :)

Take the (average) decay rate, let's say 1 decay per 2 seconds. So the
the chance of a decay in a 1-second period is 50%. Now arrage your
random-bit-generator to check for a decay during each 1 second period. A
decay: deliver a 1. No decay: deliver a 0. Voila, an - as far as we know
- perfect source of random bits.

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu



2007\10\07@163124 by David VanHorn

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> I don't think I'd bother personally, but a smoke alarm would be a
> radioactive source not too hard to get hold of. Although I can't
> say I've ever seen a scrapped one

Diet salt, potassium chloride, is fairly radioactive.

2007\10\07@174106 by Lindy Mayfield

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David Hahn came to mind when I read this.

http://en.wikipedia.org/wiki/David_Hahn



> -----Original Message-----
> From: spamBeGonepiclist-bouncesspamBeGonespammit.edu [TakeThisOuTpiclist-bouncesEraseMEspamspam_OUTmit.edu] On
Behalf
{Quote hidden}

2007\10\07@230804 by Russell McMahon

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> David Hahn came to mind when I read this.
>
> http://en.wikipedia.org/wiki/David_Hahn


Indeed.

Mantles for pressure lanterns are another source.

Some US houses have had such high Radon levels that they have had to
be abandoned.



>> > I don't think I'd bother personally, but a smoke alarm would be a
>> > radioactive source not too hard to get hold of. Although I can't
>> > say I've ever seen a scrapped one
>>
>> Diet salt, potassium chloride, is fairly radioactive.

2007\10\08@041907 by Alan B. Pearce

face picon face
>Diet salt, potassium chloride, is fairly radioactive.

So are glow in the dark watches ...

I went to an open day at a university. They had various 'radioactive' lumps
on show, and a Geiger counter that you could get 2-3 counts/sec from the
lowest to 5-10/sec for the highest. Some guy was playing with this, so I
suggested he hold the counter up to his watch. The look of surprise as the
counts shot up beyond any of the samples was something to behold.

2007\10\08@045001 by Russell McMahon

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> I went to an open day at a university. They had various
> 'radioactive' lumps
> on show, and a Geiger counter that you could get 2-3 counts/sec from
> the
> lowest to 5-10/sec for the highest. Some guy was playing with this,
> so I
> suggested he hold the counter up to his watch. The look of surprise
> as the
> counts shot up beyond any of the samples was something to behold.


Tritium is not too bad at all.

But 1940's watches used to use Radium paint.
People who wore them on the inside of their wrist (as I wear mine)
tended to develop cancer in the adjacent leg bone :-(.

Wear your genuine retro navigator watch face side out.


       Russell


2007\10\08@081603 by David VanHorn

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> Mantles for pressure lanterns are another source.

The thorium mantles aren't made anymore, at least not in the US.
:(

2007\10\08@084432 by Gerhard Fiedler

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wouter van ooijen wrote:

>> There's something that bothers me about radioactive decay being random.
>
> The fact that you can use it to deliver something that is not random
> does not disqualify it :)
>
> Take the (average) decay rate, let's say 1 decay per 2 seconds. So the
> the chance of a decay in a 1-second period is 50%.

If the average decay rate is 1 per 2 seconds, wouldn't the chance of 1
decay in a /two/ seconds period be 50%?

> Now arrage your random-bit-generator to check for a decay during each 1
> second period. A decay: deliver a 1. No decay: deliver a 0. Voila, an -
> as far as we know - perfect source of random bits.

I think for it to be perfect, you'd have to account for the reduction of
decay rate with each decay, no?

Gerhard

2007\10\08@095951 by wouter van ooijen

face picon face
> If the average decay rate is 1 per 2 seconds, wouldn't the
> chance of 1 decay in a /two/ seconds period be 50%?

I don't think so

> > Now arrage your random-bit-generator to check for a decay
> during each
> > 1 second period. A decay: deliver a 1. No decay: deliver a
> 0. Voila,
> > an - as far as we know - perfect source of random bits.
>
> I think for it to be perfect, you'd have to account for the
> reduction of decay rate with each decay, no?

Ajust the sample period accordingly...

Actually there is an error in my idea: it is biased towards 0's. For 1
extra point: explain why. For 1 more point: calculate how much it is
biased (I won't be able to check without refreshing my rusty knowledge
static, but the numerical (approximated) answer is somewhere in the
standard tables.)

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu



2007\10\08@132001 by David VanHorn

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> So are glow in the dark watches ...

The old ones are radium based, newer ones tritium (except in the US
where they are apparently worried we will assemble an H bomb with
them)

Other than that, it's Zinc Sulphide, which isn't radioactive, just
stores up light and glows for a short time.

2007\10\08@142350 by Gerhard Fiedler

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wouter van ooijen wrote:

>> If the average decay rate is 1 per 2 seconds, wouldn't the chance of 1
>> decay in a /two/ seconds period be 50%?
>
> I don't think so

Probably not, but why is it 50% in 1 second? What distribution do the
values of the intervals have? Poisson?

Anyway, these guys use an algorithm that takes this uncertainty out of the
equation: <http://www.fourmilab.ch/hotbits/how3.html>

>> I think for it to be perfect, you'd have to account for the reduction of
>> decay rate with each decay, no?
>
> Ajust the sample period accordingly...

Ah, bad idea, as is using a fixed threshold in the first place. The exact
value of the threshold depends on the material, its purity, its quantity
and several other factors.

> Actually there is an error in my idea: it is biased towards 0's. For 1
> extra point: explain why.

See the link above.

Gerhard

2007\10\09@072037 by Howard Winter

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Wouter,

On Mon, 8 Oct 2007 15:58:18 +0100, wouter van ooijen wrote:

>
> Actually there is an error in my idea: it is biased towards 0's. For 1
> extra point: explain why. For 1 more point: calculate how much it is
> biased (I won't be able to check without refreshing my rusty knowledge
> static, but the numerical (approximated) answer is somewhere in the
> standard tables.)

I was going to point this out, but read down the thread first, to find that you'd already spotted it!

The problem is that if there is more than one count in a second, you only output a single 1, so although the input average is 1 per 2 seconds, you are artificially
lowering the output average by ignoring any counts after the first.  To find out how much, you need to know the shape of the distribution - if a pulse occurred
exactly every two seconds (a flat distribution whose name I can't remember) the effect is zero, and the effect increases with the "steepness" of the distribution
graph.  It's far too long since I did statistics, so that's as far as I can go!

Cheers,


Howard Winter
St.Albans, England


2007\10\09@072736 by Howard Winter

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Russell,

On Mon, 08 Oct 2007 16:08:03 +1300, Russell McMahon wrote:

> Some US houses have had such high Radon levels that they have had to be abandoned.

Over here they've realised it's a problem, so new builds have to have a Radon survey, and based on the results steps have to be taken to mitigate the problem,
from having an impervious membrane over the building footprint to having a collecting chamber under the house with an exhaust fan.  Existing houses found to have
a serious problem can have retro-fitted measures, but it's a lot easier to do before you build!  :-)

Cheers,


Howard Winter
St.Albans, England


2007\10\09@152132 by Martin Klingensmith

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Then use a 256 bit LFSR. It's still easier than using a radioactive source.

2^(256)-1 steps before it repeats.
--
Martin K

David VanHorn wrote:
{Quote hidden}

2007\10\09@152519 by Martin Klingensmith

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FWIW I'm developing a radon detector and using a thoriated mantle
(emitting thoron) to test it.
Radon is the #2 cause of lung cancer, I bet you can guess the first.
--
Martin K

Russell McMahon wrote:
> Indeed.
>
> Mantles for pressure lanterns are another source.
>
> Some US houses have had such high Radon levels that they have had to
> be abandoned.
>  

2007\10\09@223210 by David VanHorn

picon face
On 10/9/07, Martin Klingensmith <martinEraseMEspam.....nnytech.net> wrote:
> Then use a 256 bit LFSR. It's still easier than using a radioactive source.
>
> 2^(256)-1 steps before it repeats.


But completely and absolutely NOT random.
This is how "rolling code" units work.
If I know the length of the register, and I know a couple of
sequential bytes, then I can predict the entire future and past.

2007\10\09@231437 by Martin Klingensmith

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Only if you know the scheme, seed, and samples of the resulting stream
of data. There's no way you can catalog all the data to match the
pattern, so you have to know the starting point. So while it's not
random, it's not easy to figure out what the next value is going to be.
If you want to be pedantic, I did NOT say that it was random.

I'm sure there are theoretical attacks on large LFSRs. You could hash
the output with a good hashing algorithm. Or you could use some sort of
hybrid s-box feedback instead of a XOR. It wouldn't be linear like an XOR.

--
Martin K


David VanHorn wrote:
> On 10/9/07, Martin Klingensmith <EraseMEmartinspamnnytech.net> wrote:
>> Then use a 256 bit LFSR. It's still easier than using a radioactive source.
>>
>> 2^(256)-1 steps before it repeats.
>
>
> But completely and absolutely NOT random.
> This is how "rolling code" units work.
> If I know the length of the register, and I know a couple of
> sequential bytes, then I can predict the entire future and past.

2007\10\10@100611 by David VanHorn

picon face
On 10/9/07, Martin Klingensmith <RemoveMEmartinEraseMEspamEraseMEnnytech.net> wrote:
> Only if you know the scheme, seed, and samples of the resulting stream
> of data.

I'm not sure you need the seed, though that does make it more difficult.


> If you want to be pedantic, I did NOT say that it was random.

:)  Sort of a pet peeve.  "random" means unpredictable. Radiation
decays meet that definition, at least for now.  "hard to predict, but
absolutely repeatable" is very very useful, but not random.

> I'm sure there are theoretical attacks on large LFSRs. You could hash
> the output with a good hashing algorithm. Or you could use some sort of
> hybrid s-box feedback instead of a XOR. It wouldn't be linear like an XOR.

It's a pity that nobody has taken this up, and enclosed a speck of
some long-lived alpha emitter isotope in a chip on a silicon detector.
That would be very useful.
I know the financial folks use radioactive derived sources, and I've
seen PC cards that do it, but a chip would seem pretty easy, and
shielded from all but the hottest alpha sources.

2007\10\10@102331 by Martin Klingensmith

face
flavicon
face
Doesn't it require some very sensitive electronics to count small
nuclear activity? I'm designing a radon detector, it uses a $20 opamp..
--
Martin K

David VanHorn wrote:
> It's a pity that nobody has taken this up, and enclosed a speck of
> some long-lived alpha emitter isotope in a chip on a silicon detector.
> That would be very useful.
> I know the financial folks use radioactive derived sources, and I've
> seen PC cards that do it, but a chip would seem pretty easy, and
> shielded from all but the hottest alpha sources.
>  

2007\10\10@135229 by Peter Todd

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On Wed, Oct 10, 2007 at 10:06:10AM -0400, David VanHorn wrote:
> > I'm sure there are theoretical attacks on large LFSRs. You could hash
> > the output with a good hashing algorithm. Or you could use some sort of
> > hybrid s-box feedback instead of a XOR. It wouldn't be linear like an XOR.
>
> It's a pity that nobody has taken this up, and enclosed a speck of
> some long-lived alpha emitter isotope in a chip on a silicon detector.

I somehow remember that early SRAM chips eventually reached a point
where the density was great enough that alpha particals from the minute
bits of radioactive clay in the housing was causing problems...

How much work could a simple Americanium isotope based detector be?

- --
http://petertodd.org
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2007\10\10@155733 by Al Shinn

picon face
Martin,
Small nuclear activity is one pulse at a time. I have seen single pulses
from alphas with a reverse biased silicon junction (in one case - a pin
photo detector about .1" sq.) on my old O'scope - don't remember the
size of the load resistor.
If using an ionization chamber like in a smoke detector, yes, you need
very sensitive electronics for low level work.
What sort of detector are you using for your radon?
--

Looking forward,
Al Shinn



>Doesn't it require some very sensitive electronics to count small
>nuclear activity? I'm designing a radon detector, it uses a $20 opamp..
>--
>Martin K


2007\10\10@172704 by David VanHorn

picon face
On 10/10/07, Martin Klingensmith <RemoveMEmartinspam_OUTspamKILLspamnnytech.net> wrote:
> Doesn't it require some very sensitive electronics to count small
> nuclear activity? I'm designing a radon detector, it uses a $20 opamp..

Figure the capacitance of a REALLY small PIN diode, with a dot of
AM241 or similar on it, vs a much larger diode, and hotter alpha
emitter to get through the case/coating.  The amplitude would be a lot
higher, and you could completely do the front end in that differential
mode that op-amps like so well.

I don't think it would be a big problem.

2007\10\11@221122 by Rolf

face picon face
Al Shinn wrote:
{Quote hidden}

Maybe this may help ;-)

http://xkcd.com/221/

Rolf

P.S. IANAM either ;-)

2007\10\15@030253 by Al Shinn

picon face

Well, now I am pretty sure that I am seeing alphas from a smoke detector
source ($5.50 - ~1uc americium) , with a once upon a time very good ~.1"
sq quad pin photodiode (it's been kicked around for ~ten years on my
bench with no lid , dirty, one bond wire wiped off , rats chewi...)
I hooked one end of the diode to a 9 volt battery, the other end of the
diode to the scope probe, the probe ground clip to other end of battery.
I guess the scope is a 1 mohm load. (How in bloody h&ll did they ever
get started with "w" for ohms??? )
Scope seems to have ~1.5mv of noise, pulses from diode = ~1.5 to ~3.5 mv
~300 usec decay time, ~1k pulse/s.
I don't think you need a $20 op amp for that.
Now I have to find a $.10 photodiode in a can - well <$5.00 any way :-)
I have not gotten any transistors to detect yet but will keep trying

To be 100% sure, I need a graceful means to place and remove an alpha
blocker (piece of paper) without disturbing the light leakage and etc
and etc -- the epoxy is curing as I type. My early setup was photodiode
sticking up in a proto strip with the source (and it's "native" housing)
balanced on the diode and then a bit of tape (alpha blocker) or not ---
juggle, drop, blast, hold tongue just right, DON'T TOUCH the americium
AT ALL with ANYTHING, DON'T touch the photodiode !!

Man, I really wish that turkey hadn't stolen my geiger counter the other
night - But then I may not have played with the photodiode ??

--

Looking forward,
Al Shinn







2007\10\15@050531 by Gerhard Fiedler

picon face
Al Shinn wrote:

> (How in bloody h&ll did they ever get started with "w" for ohms??? )

Look at how a lower case omega looks like
<http://en.wikipedia.org/wiki/Omega> and add a traditional confusion of
lower case with upper case symbols, and it almost makes sense :)

Gerhard

2007\10\15@104039 by Peter Bindels

picon face
On 10/10/2007, Martin Klingensmith <RemoveMEmartinTakeThisOuTspamspamnnytech.net> wrote:
> Only if you know the scheme, seed, and samples of the resulting stream
> of data. There's no way you can catalog all the data to match the
> pattern, so you have to know the starting point. So while it's not
> random, it's not easy to figure out what the next value is going to be.
> If you want to be pedantic, I did NOT say that it was random.

Berlekamp-Massey decodes the seed for any given sequence of a known
LFSR (which is a basic structure with arbitrary linear modifications)
given twice the length of bits and the length of bits. If you can
guess 64 bits of an output stream (which isn't awfully hard, given
that most of them start with whitespace or XML-ish starts) you can
decode any 32-bit LFSR.

> I'm sure there are theoretical attacks on large LFSRs. You could hash
> the output with a good hashing algorithm. Or you could use some sort of
> hybrid s-box feedback instead of a XOR. It wouldn't be linear like an XOR.

These are the practical attacks. Theoretical attacks imply that you
must include a non-LFSR source to prevent this or hide them very well,
which hasn't had much analysis yet. S-boxes don't do much good for the
output but permute the order of the repetitions and make it less
likely that you find a polynomial that gives a full result.

2007\10\15@132836 by wouter van ooijen

face picon face
> Berlekamp-Massey decodes the seed for any given sequence of a
> known LFSR (which is a basic structure with arbitrary linear
> modifications) given twice the length of bits and the length
> of bits. If you can guess 64 bits of an output stream (which
> isn't awfully hard, given that most of them start with
> whitespace or XML-ish starts) you can decode any 32-bit LFSR.

That is why the basic rule of cryptografy is: compress first, then
encrypt.

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu



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