How to fool a GPS Todd Humphreys

something happened in the early morning

hours of May 2nd 2000 that had a

profound effect on the way our society

operates ironically hardly anyone

noticed at the time the change was

silent imperceptible unless you knew

exactly what to look for on that morning

US President Bill Clinton ordered that a

special switch be thrown in the orbiting

satellites of the global positioning

system instantaneously every civilian

GPS receiver around the globe went from

errors the size of a football field the

errors the size of a small room it’s

hard to overstate the effect that this

change in accuracy has had on us before

this switch was thrown we didn’t have in

car navigation systems giving

turn-by-turn directions because back

then gps couldn’t tell you what block

you are on let alone what street for

geolocation accuracy matters and things

have only improved over the last 10

years with more base stations or ground

stations better receivers and better

algorithms GPS can now not only tell you

what street you were on but what part of

the street this level of accuracy has

unleashed a firestorm of innovation in

fact many of you navigated here today

with the help of your TomTom or your

smartphone paper maps are becoming

obsolete Boystown now stand on the verge

of another revolution in geolocation

accuracy what if I told you that the 2

meter positioning that our current cell

phones and our our tom-toms give us is

pathetic compared to what we could be

getting for dump sometime now it’s been

known that if you pay attention to the

carrier phase of the GPS signal and if

you have an internet connection then you

can go from meter love

2-centimeter level even millimeter level

positioning so why don’t we have this

capability on our on our phones only I

believe for a lack of imagination

manufacturers haven’t built this carrier

phase technique into their cheap GPS

chips because they’re not sure what the

general public would do with geolocation

so accurate that you could pinpoint the

wrinkles in the palm of your hand but

you and I and other innovators we can

see the potential in this next leap in

accuracy imagine for example an

augmented reality app that overlays a

virtual world 2 millimeter level

precision on top of the physical world I

could build for you a structure up here

in 3d millimeter accurate that only you

could see or my friends at home so this

level of positioning this is what we’re

looking for and I believe that within

the next few years I predict that this

kind of hyper precise scarrier phase

based positioning will become cheap and

ubiquitous and the consequences will be

fantastic

the Holy Grail of course is the GPS dot

do you remember the the movie The Da

Vinci Code here’s professor Langdon

examining a GPS dot which his accomplice

tells him is a tracking device accurate

within 2 feet anywhere on the globe but

we know that in the world of nonfiction

the GPS dot is impossible right

for one thing GPS doesn’t work indoors

and for another they don’t make devices

quite this small especially when those

devices have to relay their measurements

back over a network

well these objections were perfectly

reasonable a few years ago but things

have changed there’s been a strong trend

toward miniaturization better

sensitivity so much so that a few years

ago a GPS tracking device looked like

this clunky box to the left of the keys

compare that with the device released

just months ago that’s now packaged into

something the size of a key fob and if

you take a look at the state-of-the-art

for a complete GPS receiver which is

only a centimeter on a side and more

sensitive than ever

you realize that the GPS dot will soon

move from fiction to nonfiction imagine

what we could do with a world full of

GPS dots it’s not just that you’ll never

lose your wallet or your keys anymore or

your child when you’re at Disneyland

you’ll buy gps dots in bulk and you’ll

stick them on everything you own worth

more than a few tens of dollars I

couldn’t find my shoes one recent

morning and as usual I had to ask my

wife if she had seen them but I

shouldn’t have to bother my wife with

that kind of triviality I should be able

to ask my house where my shoes are those

of you who have made the switch to Gmail

remember how refreshing it was to go

from organizing all of your email to

simply searching it the GPS dot will do

the same for our possessions now of

course there is a flip side to the GPS

dot I was in my office some months back

and got a telephone call the woman on

the other end of the line we’ll call her

Carol was panicked apparently an

ex-boyfriend of Carol’s from California

had found her in Texas and was following

her around so you might ask at this

point why she’s calling you well so did

I but it turned out there was a

technical twist to Carol’s case every

time her ex-boyfriend would show up at

the most improbable times in the most

improbable locations he was carrying an

open laptop and over time Carol realized

that he had planted a GPS tracking

device on her car so she was calling me

for help

to disable it well you should go to a

good mechanic and have him take him look

at your car I said I already have she

told me he didn’t see anything obvious

and he said he’d have to take the car

apart piece by piece well then uh you

better go to the police I said I already

have she replied they’re not sure this

rises to the level of harassment and

they’re not set up technically to find

the device

okay what about the FBI I’ve talked to

them too and same story we then talked

about her coming to my lab and us

performing a radio sweep of her car but

I wasn’t even sure that would work given

that some of these devices are

configured to only transmit when they’re

inside safe zones or when the car is

moving so there we were Carol isn’t the

first and certainly won’t be the last to

find herself in this kind of fearsome

environment worrisome situation caused

by GPS tracking in fact as I looked into

her case I discovered to my surprise

that it’s not clearly illegal for you or

me to put a tracking device on someone

else’s car the Supreme Court ruled last

month that a policeman has to get a

warrant if he wants to do prolonged

tracking but the law isn’t clear about

civilians doing this to one another so

it’s not just big brother we have to

worry about but big neighbor

there is one alternative the Carroll

could have taken very effective it’s

called the wave bubble it’s a an open

source GPS jammer developed by L’Amour

freed a graduate student at MIT and

L’Amour calls it a tool for reclaiming

our personal space with a flip of the

switch you create a bubble around you

within which GPS signals can’t reside

they get drowned out by the bubble and

L’Amour designed this in part because

like Carol she felt threatened by GPS

tracking then she posted her design to

the web and if you don’t have time to

build your own you can buy one Chinese

manufacturers now sell thousands of

nearly identical devices on the Internet

so you might be thinking the way bubble

sounds great I should have one might

come in handy if somebody ever puts a

tracking device on my car but you should

be aware that its use is very much

illegal in the United States and why is

that well because it’s not a bubble at

all it’s jamming signals don’t stop at

the edge of your personal space or at

the edge

car they go on to jam innocent GPS

receivers for miles around you now if

you’re Carol or L’Amour or someone who

feels threatened by GPS tracking it

might not feel wrong to turn on a wave

bubble but in fact the results can be

disastrous imagine for example you’re

the captain of a cruise ship trying to

make your way through a thick fog and

some passenger in the back turns on a

wave bubble all of a sudden your GPS

readout goes blank and now it’s just you

and the fog and whatever you can pull

off the radar system if you remember how

to work it

they in fact they don’t update or upkeep

lighthouses anymore and Loran the only

backup to GPS was discontinued last year

our modern society has a special

relationship with GPS we’re almost

blindly reliant on it it’s built deeply

into our systems and infrastructure some

call it the invisible utility so turning

on a wave bubble might not just cause

inconvenience it might be deadly but as

it turns out for purposes of protecting

your privacy at the expense of general

GPS reliability there’s something even

more potent and more subversive than a

wave bubble and that is a GPS spoofer

the idea behind the GPS spoofer is

simple instead of jamming the GPS

signals you fake them you imitate them

and if you do it right the device you’re

attacking doesn’t even know it’s being

spoofed so let me show you how this

works in any GPS receiver there’s a peak

inside that corresponds to the authentic

signals these three red dots represent

the tracking points that try to keep

themselves centered on that peak but if

you send in a fake GPS signal another

peak pops up and if you can get these

two peaks perfectly aligned the tracking

points can’t tell the difference and

they get hijacked by the stronger

counter

signal with the authentic peak getting

forced off at this point the game is

over the fake signals now completely

control this GPS receiver so is this

really possible can someone really

manipulate the timing and positioning of

a GPS receiver just like that with a

spoofer well the short answer is yes the

key is that civil GPS signals are

completely open

they have no encryption they have no

intent ocation they’re wide open

vulnerable to a kind of spoofing attack

even so up until very recently nobody

worried about GPS spoofer x' people

figured that it would be too complex or

too expensive for some hacker to build

one but I and a friend of mine from

graduate school we didn’t see it that

way we knew it wasn’t going to be so

hard and we wanted to be the first to

build one so we could get out in front

of the problem and help protect against

GPS spoofing I remember vividly the week

it all came together we built it at my

home which means that I got a little

extra help from my three-year-old son

Ramon here’s Ramon looking for a little

attention from dad that week at first

the spoof it was just a jumble of cables

and computers though we eventually got

it packaged into a small box now the dr.

Frankenstein moment when the spoofer

finally came alive and I glimpsed its

awfull potential came late one night

when I tested the spoofer against my

iPhone

let me show you some actual footage from

that very first experiment I had come to

completely trust this little blue dot

and it’s reassuring blue halo they seem

to speak to me they say here you are

here you are

and you can trust us so something felt

very wrong about the world it was a

sense almost of betrayal when this

little blue dot started at my house and

went running off toward the north

leaving me behind I wasn’t moving what I

then saw in this little moving blue dot

was the potential for chaos I saw

airplanes and ships veering off course

with the captain learning only too late

that something was wrong

I saw the GPS derived timing of the New

York Stock Exchange being manipulated by

hackers you can scarcely imagine the

kind of havoc you could cause if you

knew what you were doing with a GPS

spoofer there is though one redeeming

feature of the GPS spoofer it’s the

ultimate weapon against an invasion of

GPS dots imagine for example you’re

being tracked but you can play the

tracker for a fool pretending to be at

work when you’re really on vacation or

if you’re Carol you could lure your

ex-boyfriend into some empty parking lot

where the police are waiting for him so

I’m fascinated by this conflict a

looming conflict between privacy on the

one hand and the need for a clean radio

spectrum on the other we simply cannot

tolerate GPS jammers and spoof errs and

yet given the lack of effective legal

means for protecting our privacy from

the GPS dot can you really blame people

from wanting to turn them on for wanting

to use them I hold out hope that we’ll

be able to reconcile this conflict with

some sort of some yet uh uninventive

technology but meanwhile grab some

popcorn because things are going to get

interesting within the next few years

many of you will be the proud owner of a

GPS dot maybe you’ll have a whole bag

full of them

you’ll never lose track of your things

again

the GPS dot will fundamentally reorder

your life but will you be able to resist

the temptation to track your fellow man

or will you be able to resist the

temptation to turn on a GPS spoofer or a

wave bubble to protect your own privacy

so as usual what we see just beyond the

horizon is full of promise and peril

it’ll be fascinating to see how this all

turns out thanks