[Cryptography] Tempest and limits on receiving

[Michael Kjörling]

On 4 Apr 2017 14:34 -0500, from wilson at math.wisc.edu (Bob Wilson):
> Several posters seem to think that in the USA there are no
> restrictions on just listening, e.g.
>> In the US laws only prohibit active interference, not passive shielding.

I don't see how what you are saying contradicts such a statement. The
fact that you can or can't buy an off-the-shelf receiver that covers a
particular frequency range has no immediate bearing on whether you are
allowed or not allowed to shield against RF or EMI. To a similar tune,
I can't readily buy an aviation band transmitter, but that doesn't
mean I'm not allowed to listen to aviation transmissions. I may or may
not be allowed to _convey the content of_ such transmissions, however.

Also, have you checked out the market for SDR (software-defined radio)
equipment lately? I'm pretty sure that you, without too much trouble,
can find ones that allow receiving your pet frequency.

> Have you tried to buy a shortwave radio that covers all of the
> frequencies from, say, 100MHz to 10GHz?

That's not shortwave. Shortwave (technically the HF range) is 3-30
MHz, and in colloquial speech it is sometimes extended to something
like 1.5-30 MHz or thereabouts, but 100 MHz is well beyond shortwave
(and has very different propagation characteristics, including e.g.
that reliable ionospheric propagation basically doesn't happen;
sporadic E-layer propagation doesn't count as reliable). The microwave
range, for comparison, begins around 2 GHz or so.

-- 
Michael Kjörling • https://michael.kjorling.se • michael at kjorling.se
                 “People who think they know everything really annoy
                 those of us who know we don’t.” (Bjarne Stroustrup)