December 2019, ScientificAmerican.com 45their GPS receivers could be spoofed from a hotel room a quarter
of a mile away. There are 55,000 substations across the U.S.^
Goward and Humphreys have warned utility executives
about the danger they face, and they say few are aware. Fewer
still, they maintain, have adequate contingency plans (some of
which also rely on GPS). Human controllers who oversee grid
networks “wouldn’t think to look at GPS as a possible source of
the problem for probably hours,” Goward says. Furthermore, he
notes, “attackers would be able to disguise what they’re doing
for quite some time.”
Blackouts are costly and dangerous, but spoofing an airplane
might provide the greatest drama. Humphreys and Eurocon-
trol’s Berz agree that it would be difficult but possible. Military
aircraft use a device called a selective availability antispoofing
module, but it is not required on civilian aircraft, and deploy-
ment is heavily restricted by the government. Lauth, who trains
air traffic controllers, told me that pilots have other options for
landing. The primary backup, however, is an airport’s instru-
ment landing system, which provides aircraft with horizontal
and vertical guidance and its distance from the landing spot.
The system operates on radio waves and was built for safety, not
security, so it is unencrypted—meaning a person can spoof it by
inducing the aircraft’s receiver to lock onto a false signal.
IMPROVING RESILIENCE
Society’S reliance on GPS will only increase. The 5G-enabled In-
ternet of Things will depend heavily on GPS because devices
need precise timing to sync with one another and across net-
works. So will the “mirror world,” a digital representation of the
real world that machines will need to produce for AI and aug-
mented-reality applications.
Although the dhS acknowledges the threat, not everyone is
pleased with what it is doing—or not doing—about it. James
Platt, director of the position, navigation and timing office at the
dhS, says the agency is working with niSt to outline varying lev-
els of security for different receiver types.^ And the dhS conducts
annual exercises that allow equipment manufacturers to test
their machines against attack. The results are not public, but Lo-
gan Scott, a consultant who has worked with GPS for 40 years,
says “a lot of receivers do not do well when exposed to jamming
and spoofing.”
Antispoofing is a burgeoning field of research, with hundreds
of papers published in the past several years. For example, dur-
ing a spoofing attack, a vestige of the true GPS signal manifests
on the receiver as distortion. Specialized receivers can monitor
such distortion and give an alarm if it is detected, but the spoof-
er can generate a signal to nullify the distortion. “There is no
foolproof defense,” Humphreys says. “What you can try is to
price your opponent out of the game” by deploying antispoofing
protections. Armed with the right equipment, though, a spoofer
can overcome them. Protections and new threats are continual-
ly evolving in a kind of arms race in the radio-frequency spec-
trum. “If your opponent happens to be the Russian Federation,”
Humphreys says, “good luck.”
An arms race could be defused if the U.S. built a backup tim-
ing system like the ones other countries maintain. In December
2018 President Donald Trump signed the National Timing Resil-
ience and Security Act, which instructs the Department of
Transportation (dot) to build a “land-based, resilient, and reli-
able alternative timing system” by 2020. But neither the act nor
the president has funded this undertaking.
The law was just the latest example of the U.S. government’s
inadequate response, say critics such as Goward and others. The
dhS issued a report on GPS vulnerability in 2001. President
George W. Bush directed the dhS and the dot to create a backup
in 2004. The deputy defense secretary and deputy transporta-
tion secretary told Congress in 2015 that they would collaborate
on a system known as eLoran (enhanced long-range navigation),
which does exactly what the 2018 bill requires. Congress funded
an eLoran pilot program years ago, but not a penny of that fund-
ing has been spent. Adam Sullivan, dot assistant secretary for
governmental affairs, told Peter DeFazio, chair of the House
Transportation and Infrastructure Committee, in a May 8 letter
that the dot “is planning to conduct a field demonstration of
technologies ... capable of providing backup [position, naviga-
tion and timing] services to critical infrastructure” by the end of- In September the dot issued a request for proposals, a
week after Senator Ted Cruz of Texas and Senator Ed Markey of
Massachusetts wrote the transportation secretary to ask what
was taking so long.
An eLoran system would render jamming and spoofing al-
most irrelevant by delivering a low-frequency radio signal that
is much stronger than GPS’s ultrahigh-frequency signal and
hence is virtually impossible to override. The plan for eLoran
would be to build about two dozen giant antennas necessary for
nationwide coverage through a public-private partnership, ac-
cording to Goward and to Representative John Garamendi of
California, who has been prodding several administrations to
act. The U.S. Air Force and the Pentagon are reportedly looking
at other potential backup systems as well. The backups that var-
ious countries maintain are all essentially versions of eLoran.
Even if work begins tomorrow, eLoran will take years to build.
It will be even longer before new devices and receivers that can
pick up the signal are designed, manufactured and delivered to
customers. “Four years is optimistic,” says Frank Prautzsch, a for-
mer director of network systems at Raytheon, who also worked
on space systems at Hughes Space and Communications.
A different global patch would be to alter GPS signals at the
satellite source with digital signatures that authenticate the data
and deploy the public-private key infrastructure common to
cryptography. But the signal coming from the current constella-
tion of satellites cannot be changed. An air force spokesperson
said no plans exist to incorporate digital signatures into the next
generation of satellites, now being built at a secure Lockheed
Martin facility west of Denver.
Despite all that, Platt is confident in critical infrastructure’s re-
silience. “We’ve talked with industry to make sure they have miti-
gation strategies in place,” he says. Goward’s response: “Suggest to
Jim that we turn GPS off for 24 hours just to see what happens.”
MORE TO EXPLORE
Above Us Only Stars: Exposing GPS Spoofing in Russia and Syria. C4ADS; March 26, 2019.
Dual-Antenna GNSS Spoofing Detection Method Based on Doppler Frequency
Difference of Arrival. Li He et al. in GPS Solutions, Vol. 23, Article No. 78; July 2019.
FROM OUR ARCHIVES
The Global Positioning System. Thomas A. Herring; February 1996.
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