GNSS message authentication

A method for authentication of GNSS messages by an authentication transmitter apparatus (20) comprising a reference receiver (22), an authentication server (24) and an authentication transmitter (26). The method comprises: receiving, by the reference receiver, a plurality of navigation messages (50) from a plurality of GNSS satellites (10); hashing, by the authentication server, the navigation messages to create a plurality of hashed messages; creating, by the authentication server, a table comprising the plurality of hashed messages; signing, by the authentication server, the table to create a signed table (70) comprising the hashed messages and acryptographic signature, and transmitting, by the authentication transmitter, the signed table to an authentication receiver apparatus (40). [FIG. 1]