US Patent 9998918 Satellite based key agreement for authentication

A method for deducing a quantity (θ), in two distinct locations, from further distinct measurable quantities. The method comprises the steps of observing with a first device (CD) the quantity (θ) from an intercepted signal, whereby the device is placed in a location with first coordinates (Xi, Yi, Zi); providing a second device (AS) in a location with second coordinates (Xs, Ys, Zs); causing the second device to transmit a signal to be intercepted by the first device (CD); whereby the second device (AS) needs to know the second coordinates and be informed of the first coordinates of the first device (CD) to calculate the quantity (θ) that can be obtained from measurements by the first device (CD); the quantity (θ) thereby being known by the second device (AS) and the first device (CD) without the need to communicate the quantity or any other value that is sufficient for a third device to deduce the quantity (θ).