How to achieve 1 meter accuracy with Android Was: Re: Dropgang vulnerabilities

jim bell jdb10987 at
Sat Feb 23 23:01:09 PST 2019

[partial quote begins]

Recent changes in hardware and standards make one-meter accuracy possible, in some cases as soon as this year. The transcript of a talk given to Android developers earlier this year, this article gives a short overview of location in smartphones, introduces Wi-Fi round-trip time technology and standards, and then explains the Wi-Fi application programming interfaces.

By Frank van Diggelen, Roy Want and Wei Wang, Android Location, Google

Eventually, this means high accuracy for everyone, but we want to take you under the hood of location because we want to give you the opportunity to get a head start on the future. We also want to highlight the need to protect and respect the user. The more people who use location, the more careful we and you have to be. We will highlight where you must get user permissions and we’ll close with some guidelines for making great location apps.It’s a great time for location applications because technology hardware standards and Android application programming interfaces (APIs) are all evolving simultaneously to enable an improved location accuracy that has not previously been possible when using smartphones.

Where are we today with indoor location accuracy? If you’ve noticed that your phone seems to be more accurate when you’re inside shopping malls and office blocks than it was a few years ago, you’re not imagining it. With each release of the fused location provider, we have had steady improvement of the Android algorithms and machine learning for Wi-Fi locations.

There continues to be improvement, and you’ll see indoor accuracy of better than 10 meters, but round-trip time (RTT) is the technology that will take us to the one-meter level.

Meanwhile, what about GPS? In terms of GPS accuracy in the open sky, there has not been much change in the last few years. If you’re outside and can see the open sky, the GPS accuracy from your phone is about five meters, and that’s been constant for a while. But with raw GNSS measurements from the phones, this can now improve, and with changes in satellite and receiver hardware, the improvements can be dramatic.

Everyone’s familiar with the blue dot, but to get the blue dot you need a location provider, and to get location you need measurements — specifically, range measurements from Wi-Fi access points or from GPS satellites. We’ll show you how one-meter measurement accuracy can be made available in smartphones. The key technologies are Wi-Fi RTT, GPS dual-frequency and carrier phase measurements.

[end of partial quote]

    On Tuesday, January 22, 2019, 11:28:08 PM PST, jim bell <jdb10987 at> wrote:  
  On Tuesday, January 22, 2019, 3:13:07 PM PST, Steve Kinney <admin at> wrote:
 On 1/13/19 10:43 PM, Mirimir wrote:
>> Dropgangs, or the future of dark markets

>Here's some ideas about structural vulnerabilities in the Dropgang
protocol, as described at

>Dead drop reuse:

>To achieve acceptable security each dead drop may be used once only,
because hostile buyers could place 'their' dead drops under video
surveillance  and record every courier and customer visit to the drop
following their own transaction.

>Couriers delivering to dead drops can not determine if their supplier
sends them to previously used dead drops, unless they service only dead
drops they set up and document themselves.  Couriers should transmit the
locations of drops they have developed only when presented with an order
to fill, to assure that their distributor can not send other couriers
and customers to use them first.  The added surveillance exposure of
making two visits to the same site - setup and delivery - presents less
exposure than trusting that the anonymous seller will never send a
courier to a previously used dead drop.
[much stuff deleted]

People who think of a 'dead drop' as being a previously-existing hidey-hole in the urban/suburban landscape need to remember that even if they are relatively plentiful, they are NOT so plentiful that they won't be reused at some point.  Or much more likely, probed on speculation by passers-by, especially once they learn that such locations may be used as dead-drops.  
This is one reason I previously described my idea to have a pointy metal or stiff-plastic  tube driven into the soil or  in grassy area, maybe 1 inch in diameter, and then filled with a removable tube with the payload contained in it.  For an approximate shape, take a look at this ad for centrifuge tube:

(Although I am not suggesting employing an actual 'centrifuge tube':  They appear to be much too expensive for this purpose.  I am merely showing the approximate simple shape that could be employed.)
Its location, when placed, is essentially arbitrary.   All cities, suburbs, and towns, to say nothing of rural areas, are quite full of parks, fields, unbuilt lots, golf courses, cemeteries, grassy medians, high-tension line rights-of-way, gravel roads, beaches, and forested areas.  Almost all of that could be employed to hide a tiny pipe whose presence would probably go unnoticed for years, and certainly for hours and days.  
The main requirement to find the store is a precise GPS system, ideally one which can employ WAAS (Wide Area Augmentation System), which usually will provide a location accuracy of 1 meters.  That alone would probably be sufficient.
If people are assumed to only have access to ordinary GPS receivers, such as those in smartphones, I have also suggested using a plastic molded "corner-cube" retroreflection device to accurately send back light (or, with an IR-only filter, IR) to the searcher.  See Acrylite GP color 1146-0.   This material can be placed over an ordinary clear-plastic retroreflector, and according to the graph shown it retroreflects only 1% of 1% (or 0.01%; it loses 99% on each pass through the sheet.)   The retroreflection plane can be 'aimed' in a specific direction, to make it even more unlikely to be accidentally found by a random passer-by.  
Another aid to finding such a cache would be to throw a few hundreds or thousands of tiny (say, 1/100 inch diameter? polished glass beads, around the target, after it was placed in a grassy area.  These glass beads would, themselves, be somewhat retroreflective, but could only be seen from above as the searcher gets close to the cache.  Or, a small retroreflection disk can be placed, face-up, at or near the cache.  
                 Jim Bell

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