  With the rapid spread of various mobile terminals in our society, the
importance of secure positioning is growing for wireless networks in
adversarial settings. Recently, several authors have proposed a secure
positioning mechanism of mobile terminals which is based on the geometric
property of wireless node placement, and on the postulate of modern physics
that a propagation speed of information never exceeds the velocity of light. In
particular, they utilize the measurements of the round-trip time of radio
signal propagation and bidirectional communication for variants of the
challenge-and-response. In this paper, we propose a novel means to construct
the above mechanism by use of unidirectional communication instead of
bidirectional communication. Our proposal is based on the assumption that a
mobile terminal incorporates a high-precision inner clock in a tamper-resistant
protected area. In positioning, the mobile terminal uses its inner clock and
the time and location information broadcasted by radio from trusted stations.
Our proposal has a major advantage in protecting the location privacy of mobile
terminal users, because the mobile terminal need not provide any information to
the trusted stations through positioning procedures. Besides, our proposal is
free from the positioning error due to claimant's processing-time fluctuations
in the challenge-and-response, and is well-suited for mobile terminals in the
open air, or on the move at high speed, in terms of practical usage. We analyze
the security, the functionality, and the feasibility of our proposal in
comparison to previous proposals.
