A method carried out in a radionavigation system, the radionavigation system comprising a receiver and a radionavigation infrastructure, the radionavigation infrastructure comprising a plurality of satellite-borne transmitters (8, 8', 8", 8'''), and an encryption component configured for communication with the transmitters (8, 8', 8", 8''') and the receiver, the method comprising, for one or more given transmitters of the plurality of satellite-borne transmitters (8, 8', 8", 8'''): generating, in the radionavigation infrastructure, a series of keys k2,i in respect of a predetermined authentication interval [0,T] of duration T and commencing at t=0; generating, in the radionavigation infrastructure, a spreading code-encrypted signal e(t) 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; generating, in the encryption component of the radionavigation infrastructure, a re-encrypted sequence Ri using a keystream K2,i generated with the series of keys k2,i and additionally an encrypted sequence extracted from signal e(t) associated to the predetermined authentication interval [0,T]; transmitting, prior to t = 0, by the encryption component, the re-encrypted sequence Ri to the receiver; transmitting, from the given transmitter, the spreading code-encrypted signal e(t); transmitting, from one of the plurality of transmitters (8, 8', 8", 8'''), the series of keys k2,i and receiving and storing, at the receiver, prior to t = 0, the re-encrypted sequence Ri; receiving, at the receiver, the spreading code-encrypted signal e(t); receiving, at the receiver, the series keys k2,i decrypting, at the receiver, the re-encrypted sequence Ri using the series of keys k2,i to obtain encrypted sequences Ei; and correlating, at the receiver, at least portions of the received the spreading code-encrypted signal e(t) with the encrypted sequences Ei and thereby generating a code phase measurement for the given transmitter. generating, in the radionavigation infrastructure, a series of keys k2,i in respect of a predetermined authentication interval [0,T] of duration T and commencing at t=0; generating, in the radionavigation infrastructure, a spreading code-encrypted signal e(t) 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; generating, in the encryption component of the radionavigation infrastructure, a re-encrypted sequence Ri using a keystream K2,i generated with the series of keys k2,i and additionally an encrypted sequence extracted from signal e(t) associated to the predetermined authentication interval [0,T]; transmitting, prior to t = 0, by the encryption component, the re-encrypted sequence Ri to the receiver; transmitting, from the given transmitter, the spreading code-encrypted signal e(t); transmitting, from one of the plurality of transmitters (8, 8', 8", 8'''), the series of keys k2,i and receiving and storing, at the receiver, prior to t = 0, the re-encrypted sequence Ri; receiving, at the receiver, the spreading code-encrypted signal e(t); receiving, at the receiver, the series keys k2,i decrypting, at the receiver, the re-encrypted sequence Ri using the series of keys k2,i to obtain encrypted sequences Ei; and correlating, at the receiver, at least portions of the received the spreading code-encrypted signal e(t) with the encrypted sequences Ei and thereby generating a code phase measurement for the given transmitter.