MATTER & ENERGY
Quantum data locking demonstrated
Long encrypted message can be sent with short decoding key
BY LAUREL HAMERS
Researchers have built a modern-day
Enigma machine that relies on the quirky
laws of quantum mechanics instead
of the rotors and levers of the famous
World War II–era code machines. It’s the
first experiment to show that it’s possible
to send large amounts of secure quantum data protected by a much shorter
secret key, the team reports August 12 in
Physical Review A.
Encryption usually relies on a secret
key shared between two parties. The
sender uses the key to scramble the message so it looks random to an outsider; the
receiver uses the key to unscramble it. An
eavesdropper who doesn’t have the key
can’t read the garbled message.
Spies can use quantum mechanics to
generate secure keys that can’t be cracked
by even the most powerful computers.
Instead of 1s and 0s, quantum keys use
the spins of photons, tiny packages of
light. But those keys must be at least as
long as the message they’re protecting.
“It’s very powerful, but it’s very
impractical if you’re trying to transmit
a dictionary or a volume of information,”
says Daniel Lum, a quantum physicist at
the University of Rochester in New York.
By encoding the message itself (and
not just the key) in a quantum system,
it’s theoretically possible to protect a
long string of data using a much shorter
key. The idea, called quantum data locking, was first proposed about 10 years
ago. But nobody had experimentally
tested it until now because of the challenges of actually sending inherently
unstable quantum information.
Lum and colleagues built a setup that
shoots a photon at a detector. To dis-
guise the message encoded inside the
photon, the sender scrambles the wave
pattern of the photon so that it can’t be
focused onto a single point on the detec-
tor. The receiver knows the equation
that the sender has used to disguise the
wave and can therefore use the inverse
function to cast off that disguise. Then
the photon will land at the spot on the
detector where it was intended to, and
the receiver can read the message.
The eavesdropper doesn’t know the
equation, which acts like a key. Test-
ing different keys to find the right one
won’t work; one wrong guess messes up
the message because measuring a quan-
tum system changes it. And there are so
many different ways the message could
be scrambled that the odds of guessing
correctly with one try are practically zero.
The sender still needs a secure method
to get the first key to the receiver. But
once that ball is rolling, the sender can
embed a new, shorter key in each quan-
tum message, which the receiver can
then use to unlock the next missive.
Quantum data locking has potential
drawbacks. The experiment assumes
that the eavesdropper has infinite com-
puting power but limited quantum
memory and so can’t collect lots of infor-
mation over time about the messages
and put it all together to crack the code.
“In terms of people’s technical capa-
bilities, this is a very reasonable assump-
tion,” says study coauthor Seth Lloyd, a
quantum mechanical engineer at MIT.
But it’s not fail-safe.
Applying this kind of data locking in
the real world might be difficult. “What’s
really neat about data locking is that it
does allow you to encrypt at essentially
zero cost,” says Stanford University
quantum physicist Patrick Hayden. “But
there are caveats to it. And in reality, the
type of security that you achieve this way
is delicate.” Hayden thinks most people
wanting to be certain that their messages remain private would probably
pick a different quantum protocol. s
Betty, a New Caledonian crow heralded as a toolmaking prodigy, may not
have been such a whiz bird after all. Her apparently spontaneous wire bending is getting a closer look based on new information about wild birds.
As a lab resident, Betty astounded researchers over a decade ago by
bending a wire into a hook — with no obvious design cues or known experience — and then using the hook to get a treat from a tube. The wire bending
became “one of the most compelling demonstrations of insightful behavior in
nonhumans,” says Christian Rutz of the University of St. Andrews in Scotland.
But tests of wild New Caledonian crows temporarily held in a field aviary raise
the possibility that Betty may have bent twigs before coming into the lab,
Rutz and colleagues say in the August Royal Society Open Science.
Of 18 wild Corvus moneduloides crows, 10 bent a pliable stick to use as a
tool. (A wild crow using a hook to snag an insect is shown above.) Betty had
also been caught in the wild and may have had some experience with bending
pliable tools. The observations don’t disprove that she invented wire bending
spontaneously but raise an alternative explanation, Rutz says. — Susan Milius
LIFE & EVOLUTION