[15487] in cryptography@c2.net mail archive
RE: Satellite eavesdropping of 802.11b traffic
daemon@ATHENA.MIT.EDU (Trei, Peter)
Fri May 28 13:24:43 2004
X-Original-To: cryptography@metzdowd.com
X-Original-To: cryptography@metzdowd.com
Date: Fri, 28 May 2004 11:39:11 -0400
From: "Trei, Peter" <ptrei@rsasecurity.com>
To: "R. A. Hettinga" <rah@shipwright.com>,
"John Kelsey" <kelsey.j@ix.netcom.com>, <cypherpunks@minder.net>,
<cryptography@metzdowd.com>
R. A. Hettinga
> At 12:35 PM -0400 5/27/04, John Kelsey wrote:
> >Does anyone know whether the low-power nature of wireless=20
> LANs protects
> >them from eavesdropping by satellite?
>=20
> It seems to me that you'd need a pretty big dish in orbit to=20
> get that kind
> of resolution.
>=20
> The Keyholes(?) are for microwaves, right?
>=20
> 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=20
0.125 watts (GSM1800), but it is normal for the=20
power used to be one hundredth of this maximum=20
or less.
However, the base stations are much more powerful -=20
50 watts. I suspect the spy-from-orbit stuff looks=20
at this, not the phone transmitter. 802.11b/g=20
typically runs around 0.1 watt, and there is no=20
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=20
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.=20
I suspect that eavesdropping on 802.11b/g from=20
orbit is pretty hard. The power levels are very=20
low, and there may be several nets running on the same=20
channel within a satellites' antenna footprint.=20
My summary: Very tough. Probably not impossible.
Peter
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