A system obtains navigation data for Galileo from at least one terrestrial apparatus. The obtained navigation data corresponds to navigation data transmitted by a Galileo satellite. The system assembles assistance data comprising navigation data for Galileo and further data in an interrelated manner such that a message authentication codes (MACs) included for the navigation data for Galileo is usable for verifying authenticity of the further data as well. The system transmits the information to a device, which verifies the authenticity of the included navigation data for Galileo based on the MACs. Only in case the navigation data for Galileo in the assistance data is determined to be authentic, it considers the further data to be authentic.