On Fri, Feb 5, 2016 at 7:23 PM coderman <coderman@gmail.com> wrote:

On 2/5/16, Sean Lynch <seanl@literati.org> wrote:
> ... Radio is being used right now to provide anonymity, but it's being used[1]
> to hide endpoints similar to the duct-taped payphone trick depicted in
> Hackers, in order to avoid attacks like the one used to capture Ross
> Ulbricht without giving him a chance to wipe his computer (they snuck up
> behind him and pinned his arms, but they would have just rushed him had
> that not been possible). If you use a device like the ProxyHam and you sit
> somewhere where you can see it, there's a reasonable chance you'd spot
> someone who's trying to find you, giving you a chance to hit your panic
> button and escape.

this assumes you're keeping it under constant supervision, of course :P

Indeed. Having a spotter there is probably the best solution.

Alternatively, if you aren't too clumbsy or forgetful, is to have a some sort of hidden/innocuous band tied to you and to your device (e.g., a laptop) that when pulled too hard (like a grenade pin) starts the wiping process. So if you are jumped/pinned the process starts before the attackers realize it.

> The older, lower-tech version of this trick is to use a high-gain antenna
> like the Cantenna or a Yagi to use a public wifi AP from a stealthy,
> defensible location. The problem with this is that this presents no
> challenge to RDF (radio direction finding) equipment designed for WiFi.
> That's the big advantage of the ProxyHam, since whoever is looking for you
> probably won't know in advance what frequency you're using. And solving
> that problem in a general way requires MUCH more expensive gear than just
> locating WiFi clients.

one of my favorite tricks, but rather rude in spectrum,
is setting high power amplifier to maximum. DF tends to see this
signal arriving from all around... *grin*

this introduces it's own trade-offs, of course.

This is why you use an attenuator. I wouldn't think law enforcement DF equipment would be fooled by such a thing, since for example FCC will often be looking for people who are outputting too much power, which on the ham bands is going to be multiple kilowatts (I think they've mostly given up on CB except when it starts interfering with licensed users).

> It MAY be possible to use SDR to achieve LPI while still remaining within

if you're building LPI, you don't give a fuck about the FCC (compliance).
by definition, if they've found you, you fucked up!

+1

Perhaps, but I'm not about to suggest that anyone break the law.

> Actually, that gives me an idea: MIMO precoding[2] (versus spatial
> multiplexing, which is useless for your purposes). MIMO precoding devolves
> to beam-forming in the absence of reflectors like buildings, but in an
> urban environment, you get a complex combination of signal paths,
>
> MIMO precoding requires a "training" phase where they discover one another
> by transmitting some easily "locked-onto" signal so that each receiver can
> find the other transmitter independently.

it is now possible for a professional's budget to accodomate the SDR
equipment necessary to do this type of phase sync'ed active beam
forming MIMO transmission, and not all methods require the training
phase. in fact, omission of this (by out of band training, in a sense)
in a method of "keying" phased delivery of UWB MIMO in a way more
likely to achieve LPI.

A related LPI method is to use a separate, well disciplined, carrier (in-band, co-located or not) that participant devices listen to and use the sync their clocks and/or their codes. If used carefully Eve won't know about it and will find it too difficult to synch in time catch Alice and Bob's comms.

How do you train out of band? By modelling the environment? That's an interesting thought, and I suspect Google Earth has enough data to be able to do it in a lot of places. Are you aware of free or inexpensive software packages for doing this?

synthetic aperature millimeter wave vision systems are also pushing
along this boundary, for cross-pollination of suitable phased sync'ed
UWB MIMO signal processing.

Aren't you just talking phased array for something like this though? Or do you mean using phase information from the receive antennas to reconstruct the environment rather than using phasing at the transmit side to steer your beam? That's a very interesting idea since it can give you a 360 degree view with no need to steer your beam, in the same way that some blind humans can use clicks to get a picture of their entire environment. (I use humans and not bats because I think bat sonar is pretty directional, whereas human ears can localize sound quite precisely without any need to turn one's head.)

Beam stearing be accomplished much cheaper than via a phased array using nearfield plasmas to block or steer the beam. For example, a vertical cluster of flourescent tubes surrounding a simple dipole can, with proper circuitry, quickly switched so that only one of the tubes is "off" (transparent) at a time allowing incoming/outgoing signasl to only propagate in that direction. The other tubes are "on" and reflect the signals.

i could go on, if you're curious, but perhaps on another list? :)

This is definitely an area I'm interested in, so I'd love to hear more of your ideas, as may Jeremy, so if it's beyond what is generally tolerated on this list, private email would be fine, or if you have a list in mind I'd be happy to subscribe if I'm not already.