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 . <EOS>