Photo: M. Scott Brauer
of Americans have implantable medical devices, from pacemakers and
defibrillators to brain stimulators and drug pumps; worldwide, 300,000 more
people receive them every year. Most such devices have wireless connections, so
that doctors can monitor patients’ vital signs or revise treatment programs.
But recent research has shown that this leaves the devices vulnerable to
attack: In the worst-case scenario, an attacker could kill a victim by
instructing an implantable device to deliver lethal doses of medication or
the upcoming Sigcomm conference, researchers from MIT and the Univ. of
Massachusetts-Amherst (UMass) will present a new system for preventing such
attacks. The system would use a second transmitter to jam unauthorized signals
in an implant’s operating frequency, permitting only authorized users to
communicate with it. Because the jamming transmitter, rather than the implant,
would handle encryption and authentication, the system would work even with
researchers envision that the jamming transmitter—which they call a shield—would
be small enough to wear as a necklace or a watch. A device authorized to access
the implant would send encrypted instructions to the shield, which would decode
and relay them.
implantable medical devices weren’t built with hostile attacks in mind, so they
don’t have built-in encryption. But even in the future, says Dina Katabi, an
associate professor in MIT’s Department of Electrical Engineering and Computer
Science, handling encryption externally could still prove more practical than
building it directly into implants. “It’s hard to put [encryption] on
these devices,” Katabi says. “There are many of these devices that are
really small, so for power reasons, for form-factor reasons, it might not make
sense to put the [encryption] on them.” Moreover, Katabi points out,
building encryption directly into the devices could be dangerous. In an
emergency, medical providers might need to communicate with the implant of an
incapacitated patient, to retrieve data or send new instructions. Retrieving an
encryption key from the patient’s ordinary medical provider could introduce
fatal delays, but with the MIT-UMass system, an emergency responder would
simply remove the patient’s shield.
Katabi and her graduate students Shyam Gollakota and Haitham Hassanieh, working
together with Kevin Fu, an assistant professor of computer science at UMass,
and his student Ben Ransford, conducted a series of experiments using
implantable defibrillators obtained secondhand from Boston-area hospitals.
Programmable off-the-shelf radio transmitters simulated the shield.
key to the system, Katabi explains, is a new technique that allows the shield
to simultaneously send and receive signals in the same frequency band. With
ordinary wireless technology, that’s not possible: The transmitted signal would
interfere with the received signal, rendering it unintelligible. Researchers at
Stanford Univ. recently demonstrated a
transmitter that could send and receive at the same time, but it required three
antennas whose distance from each other depended on the wavelength at which
they were operating. For medical-device frequencies, the antennas would have to
be about a half a meter apart, making it impossible to miniaturize the shield.
MIT-UMass system uses only two antennas and clever signal processing that
obviates the need to separate them. “Think of the jamming signal that we
are creating as a secret key,” Katabi explains. “Everyone who doesn’t
know the secret key just sees a garbage signal.” Because the shield knows
the shape of its own jamming signal, however, it can, in effect, subtract it
from the received signal.
medical-device companies will invest in security systems like Katabi and Fu’s—and
whether patients will be willing to carry shields around with them—probably
depends on how grave they consider the threat of attack to be. Katabi
acknowledges that no such attacks have been documented to date. On the other
hand, the Federal Communications Commission has recently moved implantable
medical devices to a new frequency band that makes wireless communication with
them possible across much greater distances.
is exactly the time when you want to do this kind of research,” says
Stefan Savage, a professor in the computer science and engineering department at
the Univ. of California
at San Diego,
and one of the leaders of the department’s Security and Cryptography Group.
“You don’t want to do it when there’s an active threat.” Savage sees
no obvious technical obstacles to the deployment of the MIT-UMass system:
“I think that’s what people liked about it,” he says, “that you
could do it with existing devices, and that you did not have a lot of the
overhead that it would take to come up with an entirely new thing.” The
question, he says, is whether manufacturers will have an incentive to absorb
the cost of deploying it. “Value in the information-security market gets
created by one of two people: bad guys, or regulatory bodies,” he says.
“You want to develop the technology in advance of the threat, but absent
the threat, how do you sell the technology?”