R. A. Hettinga

> At 12:35 PM -0400 5/27/04, John Kelsey wrote:
> >Does anyone know whether the low-power nature of wireless 
> LANs protects
> >them from eavesdropping by satellite?
> 
> It seems to me that you'd need a pretty big dish in orbit to 
> get that kind
> of resolution.
> 
> The Keyholes(?) are for microwaves, right?
> 
> Cheers,
> RAH

I don't claim great expertise, but....

802.11b/g operates in the microwave range - My home
net falls over every time my kid heats up a
burrito (It comes right back, though).

GSM phones run at a MAX of 0.25 watts (GSM900) or 
0.125 watts (GSM1800), but it is normal for the 
power used to be one hundredth of this maximum 
or less.

However, the base stations are much more powerful - 
50 watts. I suspect the spy-from-orbit stuff looks 
at this, not the phone transmitter. 802.11b/g 
typically runs around 0.1 watt, and there is no 
high-power base station.

If this is the case, then the power in an 802.11b/g
net is 1/500th of that for GSM phones - which seems
to fit in with the difference in range. Phones 
operate with kilometers to the base station, while
802.11b/g is lucky to cover a whole house.

A big antenna would obviously be a lot of help, but a
smaller one a lot closer would be better. If you insist
on listening from orbit, geosync is probably not the way
to go - you'd want something like the Iridium constellation
of low-orbit sats (600 miles up).

Clarke orbit (geosync) is about 35800 km up. You'd get
a 10,000 fold advantage by putting your spysats at only
358km. 

I suspect that eavesdropping on 802.11b/g from 
orbit is pretty hard. The power levels are very 
low, and there may be several nets running on the same 
channel within a satellites' antenna footprint. 
My summary: Very tough. Probably not impossible.

Peter

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