Patent ID: 11385355

Abstract:
A method carried out in a radionavigation system (2), the radionavigation system (2) comprising a receiver (4) and a radionavigation infrastructure (6), the radionavigation infrastructure comprising a plurality of satellite-borne transmitters (8, 8′, 8″, 8′″), and encryption component (10) configured for communication with the transmitters (8, 8′, 8″, 8′″) and the receiver (4). The method comprises the following, for one or more given transmitters (8) of the plurality of satellite-borne transmitters (8, 8′, 8″, 8′″). In the radionavigation infrastructure (6), a series of keys k2,i are generated in respect of a predetermined authentication interval [0,T] of duration T and commencing at t=0 and a spreading code-encrypted signal e(t) is generated from a first radionavigation signal s1(t) using a keystream K1(t), the keystream K1(t) being generated with a secret key k1 of the radionavigation infrastructure (6). The method further comprises generating, in the encryption component (10) of the radionavigation infrastructure, a re-encrypted sequence Ri using a keystream K2,i generated with the series of keys k2,i. The method further comprises the encryption component (10) transmitting, prior to t=0, the re-encrypted sequence Ri to the receiver (4). The method further comprises transmitting, from the given transmitter (8), the spreading code-encrypted signal e(t) and transmitting, from one of the plurality of transmitters (8, 8′, 8″, 8′″), the series of keys k2,i. The method further comprises, at the receiver (4), (i) receiving and storing, prior to t=0, the re-encrypted sequence Ri; (ii) receiving the spreading code-encrypted signal e(t); (iii) receiving the series of keys k2,i; (iv) decrypting the re-encrypted sequence Ri, using the series of keys k2,i to obtain encrypted sequences Ei. The method further comprises, correlating, at the receiver (4), at least portions of the received spreading code-encrypted signal e(t) with the encrypted sequences Ei and thereby generating a code phase measurement for the given transmitter (8). The method may further comprise extracting, at the component (10), from the spreading code-encrypted signal e(t), a plurality of encrypted sequences Ei associated with respective periods of time within the predetermined authentication interval [0,T], wherein the re-encrypted sequence R′i is generated from the extracted encrypted sequences Ei using the keystream K2,i, the re-encrypted sequence Ri being associated with the given transmitter (8). In an embodiment, the encryption component (10) at which the re-encrypted sequence Ri is generated is a ground-based server. Methods carried out in the infrastructure (6) and at the receiver (4), and a radionavigation system (2), infrastructure (6) and receiver (4) are also disclosed.