By Dan Goodin in San Francisco
3rd August 2010
Researchers say they have devised a foolproof way to encrypt messages
that can be unlocked only by a recipient physically located in a
specific place, solving a problem that has vexed cryptographers for
The technique for position-based quantum cryptography is scheduled to be
presented at the 2010 IEEE Symposium on Foundations of Computer Science
in October. It makes it theoretically possible for people to securely
encrypt and decrypt messages without the use of pre-shared keys.
Instead, the messages would be encrypted using keys based on a
recipient's physical presence at a secure facility.
"The aim of position-based cryptography is to use the geographical
position of a party as its only credential," the researchers wrote in
their paper. "This has interesting applications, e.g., it enables two
military bases to talk to each other over insecure (i.e., neither
private nor authenticated) channels and without having any pre-shared
key, with the guarantee that only parties within the bases learn the
content of the conversation."
The technique builds off of previously reported research that suggested
position-based crypto was impossible to pull off against multiple
colluding adversaries scattered in different places. The researchers
solved this problem by devising a way to use quantum mechanics to
determine a party's location that can't be spoofed.
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