Patent ID: 7783451

Claim:
A processing arrangement for ascertaining whether a set of measurements is acceptable as not being under relay attack for use in determining a time of flight of signals between first and second devices, the processing arrangement configured (i) to determine, measure or calculate a value of a first time difference between first and second times of transmission of respective first and second signals transmitted from a first device, the time of transmission of the second signal being chosen randomly or from a pseudo-random sequence, (ii) to determine, measure or calculate a value of a second time difference between first and second times of arrival of one selected from the group consisting of (ii)(a) the first and second signals received at a second device along a direct path between the first and second devices and (ii)(b) other first and second signals received at the second device along an indirect path between the first and second devices via a relaying device, wherein the other first and second signals comprise copies of the first and second signals delayed in time and transmitted by the relaying device in carrying out a relay attack, and (iii) to determine whether the value of the second time difference falls within a range of expected values based upon (iii)(a) the value of the first time difference and (iii)(b) a predefined condition, wherein responsive to the value of the second time difference falling within the range of expected values, the processing arrangement ascertains the set of measurements acceptable for use in determining the time of flight of signals between the first and second devices, otherwise the processing arrangement dismisses the set of measurements as unacceptable, signifying the relay attack.