On 25 Sep 2003 06:23:38 -0700, Kevin Brooks wrote:
(phil hunt) wrote in message ...
On 23 Sep 2003 20:00:32 -0700, Kevin Brooks wrote:

No. Paul is correct, DF'ing a "frequency agile" (or "hopping")
transmitter is no easy task. For example, the standard US SINCGARS
radio changes frequencies about one hundred times per *second*,

Bear in mind that I'm talking about automated electronic gear here,
not manual intervention. Electronics works in time spans a lot
quicker than 10 ms.

So what? Unless you know the frequency hopping plan ahead of time
(something that is rather closely guarded), you can't capture enough
of the transmission to do you any good--they use a rather broad
spectrum.

OK, I now understand that DF generally relies on knowing the
frequency in advance.

BTW, when you say a rather broad spectrum, how broad? And divided
into how many bands, roughly?

It uses the entire normal military VHF FM spectrum, 30-88 MHz. ISTR
that the steps in between are measured in 1 KHz increments, as opposed
to the old 10 KHz increments found in older FM radios like the
AN/VRC-12 family, so the number of different frequencies SINGCARS can
use is 58,000.

More than one 1 kHz slot is likely to be in use at anyone time,
since you need enough bandwidth for voice. Say 20, then about
1/3000th of the frequency space is in use at any one time.

Modern crypto is good enough to withstand all cryptanalytic
attacks.

Only if it were so...but thank goodness it is not.

Oh? So who can break AES/Rijndael?

Otherwise we would
have lost the value of one of our largest and most valuable intel
programs, and NSA would no longer exist. Even the cypher keys used by
our modern tactical radios (said keys being generated by NSA at the
top end, though we now have computers in the field capable of "key
generation" using input from that source) are not
unbreakable--instead, they are tough enough to break that we can be
reasonably assured that the bad guys will not be able to gain any kind
of *timely* tactical intel; enough computing power in the hands of the
crypto-geeks and they can indeed break them,

True, but "enough" happens to be more than all the computers in
existance right now, or likely to exist.

Assume: there are 1 billion computers, each of which can check 1
billion keys/second.

Then a brute-force search on a 128-bit keyspace would take about
10^60 years.

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