Patent ID: 7237110

Claim:
An authentication system comprising an authentication apparatus and an authentication target apparatus both of which observe a radio wave from a common radio star at a common observation time, wherein: (a) said authentication apparatus observes a radio wave from the common radio star at the common observation time; (b) said authentication target apparatus observes a radio wave from the common radio star at the common observation time, and sends an information message including information on the observed radio wave to said authentication apparatus; and (c) said authentication apparatus receives the information message sent from said authentication target apparatus, applies two-dimensional fast Fourier transform in the direction of delay time axis and in the direction of delay time ratio axis to the information on the radio wave observed by said authentication target apparatus included in the received information message and information on the radio wave observed by said authentication apparatus at each time difference, estimates two intersection positions of a common wavefront delay line and a common delay time ratio line on the earth, from the peak of the result of the two-dimensional fast Fourier transform, and settles authentication for the information message as a success in a case where a position of said authentication target apparatus which is retained in said authentication apparatus in advance and one of the estimated two intersection positions correspond to each other within a predetermined error range.