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Posted by Winged on December 13, 2005, 11:36 pm
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>
>
>>>>>The putative effects of interference are frequently overestimated.
>>>>>It is electronic child's play to filter interference and even,
>>>>>given the enormous redundancy in many signals, to extract
>>>>>information many decibels *below* the noise floor.
>>>>
>>>>"Child's play"? Gotta have a cite for that one.. admittedly, I'm
>>>>assuming that the box is somewhere close to the CRT and keyboard.
>>>
>>>Here's one example of a "canned solution" extracting signals from
>>>noise using FFT integration. This particular device concentrates on
>>>audio but the processes are quite general and apply to virtually all
>>>signal processing. Hell, these things are now pretty standard - they
>>>last were cutting edge when I read about them in Aviation Week in the
>>>60s!
>>>
>>>http://www.baudline.com/manual/process.html
>>
>>And hardly the same level of complexity! Being able to integrate a
>>cuboid doesn't mean that you can provide a pure solution for, say, a
>>four-way partial differential equation
>>
>>Not that I'm saying it *can't* be done, of course - after all, aren't
>>weather forecasts 100% accurate? ;o)
>
>
>
>
> An FFT is an FFT is an FFT is an FFT! (with apologies to Gertrude Stein
> :-)
>
> The technique is *very broadly applicable* to extracting signals that
> contain redundancy from below the noise floor in *many* areas of signal
> processing. It is one of a family of time & frequency domain transform
> techniques widely used in DSP. See, for instance, a discussion of their
> application with emphasis on radar in:
>
> Time-frequency Transforms for Radar Imaging and Signal Analysis
> http://www.scitechpub.com/Chen_Time_Freq.htm
>
> As for partial differential equations, all of E&M reduces to Maxwell's 4
> differential equations. And I've solved a few cases of them (trivial
> cases just for waveguides). Instead, my differential equation solving
> usually deals with the nastier Navier-Stokes differential equations
> applicable to fluid dynamics. But, really, all this is beside the point;
> DEs have only a tangential bearing on the issues we're discussing.
>
> As an index of how commonplace an EE problem extracting signals from
> noise is, googling for it gives almost a million hits! Here's one
> example drawn at random that discusses how an entire technology, spread-
> spectrum transmission, depends on the ability to extract signals from
> noise:
>
> Open Spectrum: A Path to Ubiquitous Connectivity
> http://acmqueue.com/modules.php?name=Content&pa=showpage&pid=37
>
>
>
>>>>>I disagree. Few have access to Tempest kit to make observations,
>>>>>other than illustrations in manufacturers' brochures (which
>>>>>disclose little other than the obvious).
>>
>>>>Few != None
>>>>
>>>>Some of us may well have used such equipment for years (hint, hint)
>>>>
>>>>See above for the trivial classification level, at least here in
>>>>the UK.
>>>
>>>
> ....snip...
>
>>For the third time of saying - the classification level is the lowest
>>level possible, at least for the basics (i.e. how to build it). And
>>the techniques used aren't exactly cutting-edge, either. Nor the
>>materials.
>>
>>Have to say that I can't really understand your problem, if you've
>>ever used such kit. Which may or may not be likely, based on simple
>>age - it's far more common these days to shield the building and use
>>off-the-shelf equipment, except for the higher-classification
>>networks. Even then, a small amount of proximity control goes an awful
>>long way.
>
>
>
>
> I've used 'em but only briefly - but I've never been under the hood in
> the sense of taking one apart (the lads there frowned on those taking
> such liberties :-)
>
> However,hubris is the vice the Greek gods punished most severely. It is
> unwise to believe that a nickel's worth of math, electronics, a
> tinkerer's enthusiasm, and a few parts suppliers' catalogues, can create
> good emsec shielding. There's just a little more to it than that.
>
> Any fool can apply general principles to shielding and get, perhaps, 20
> dB of suppression. However, achieving 100 dB takes enormous attention to
> detail. General shielding is easy (that's why any fool can get 20 dB)
> but finding and closing all the leakage paths (even from, say, flexing
> causing inadequate compression of RF sealing gaskets) is distinctly non-
> trivial (and that's why any fool cannot get 100 dB). And building
> without testing to ensure one has achieved one's objective is folly. And
> testing is f**king expensive - there are relatively few certified labs
> and even some Tempest builders outsource the testing rather than carry
> the expense and bother!
>
> As just one example, it is expensive and difficult to get the special
> metallic-deposition-layer glass used for emsec shielding where visibility
> is required (e.g., screens). The specialized manufacturers don't want to
> deal in small quantities and it's awkward to ship (including lots of
> paperwork if borders are crossed).
>
> Now, none of this says emsec shielding can't be done - it IS being done
> every day - has been for decades. But by *specialty* firms. If you
> need the technology there's no sense jacking around trying to cobble up
> these things oneself - just pony up the cash and buy one from Siemens or
> Cordsen or Emcom (the ones I've used) or whomever.
>
> But before you whip out your chequebook consider whether the not
> inconsiderable sums of money could be better spent on other aspects of
> your security - in almost all cases, unless you are as rich as Croesus,
> you will find yourself deferring the purchase of those Tempest toys.
>
>
> Moving on to your comment on proximity control, I can only presume you
> have a Real Estate licence and are hoping to cash in. Increasing the
> distance by a factor of 10 only gives a 20 dB drop in signal strength; a
> distance factor of 100 gives 40 dB, 1000 give 60 dB, and 100,000 gives
> 100 dB! Most of us do not own hundreds of square miles of Nevada desert
> in order to get 100 dB signal reduction through "proximity control" - it
> is only a supplementary method that, in practice, might save you one
> zone.
>
> No, for a real-world discussion of emsec and some of the issues that bear
> on it let me direct you to the following recent paper by one of Ross
> Anderson's disciples:
>
> Security Limits for Compromising Emanations
> www.cl.cam.ac.uk/~mgk25/ches2005-limits.pdf
>
> Regards,
>
>
I gotta live more dangerous n get me a secret....I have been in Venus
rooms..not much fun and always stuffy, in several ways... If one wants
tempest buy it. If your laying out the cash for the equipment, room
mods etc, you should not neglect the security system and trusted guys
(always must be more than one) with guns who are anxious to shoot
someone and like no one. The room mods and the appropriate crypto gear
to secure the data and transmit it securely to some other equally secure
environment. Of course perimeter zoning must be controlled even with
tempest (tempest only addresses one of many security issues).
After one has invested these funds you have to wonder if paper and
pencil might not have been a better solution...
I just gotta get me a secret
As to waveguides and magnatrons, the PFM factor is sufficient for me, it
makes my head hurt..I have a difficult enough time figuring what
process is calling a specific generic dll and exactly what the process
is doing.
There are a couple graphic files floating around the net at the moment
that are quite remarkable in their activity...that actually also display
a graphic. I already know there are bright bulbs out there... I am not
convinced that the graphic decompression engine problem is totally fixed
even with the latest MS patch.
Winged
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