Pacific Institute for the Mathematical Sciences - PIMS

Position-based cryptography

Abstract

On 20 July 1969, millions of people held their breath as they
watched, live on television, Neil Armstrong set foot on the Moon. Yet
Fox Television has reported that a staggering 20% of Americans have had
doubts about the Apollo 11 mission. Could it have been a hoax staged by
Hollywood studios here on Earth? Position based cryptography may offer a
solution. This kind of cryptography uses the geographic position of a
party as its sole credential. Normally digital keys or biometric
features are used. A central building block in position-based
cryptography is that of position-verification. The goal is to prove to a
set of verifier that one is at a certain geographical location.
Protocols typically assume that messages can not travel faster than the
speed of light. By responding to a verifier in a timely manner one can
guarantee that one is within a certain distance of that verifier. Quite
recently it was shown that position-verification protocols only based on
this relativistic principle can be broken by attackers who simulate
being at a the claimed position while physically residing elsewhere in
space. Because of the no-cloning property of quantum information
(qubits) it was believed that with the use of quantum messages one could
devise protocols that were resistant to such collaborative attacks.
Several schemes were proposed that later turned out to be insecure.
Finally it was shown that also in the quantum case no unconditionally
secure scheme is possible. We will review the field of position-based
quantum cryptography and highlight some of the research currently going
on in order to develop, using reasonable assumptions on the capabilities
of the attackers, protocols that are secure in practice.

Location: SB 142