An apparatus assembles positioning assistance data using a predetermined version of a set of values of parameters. The positioning assistance data relates to radio signals of a particular positioning support device. The apparatus encrypts the positioning assistance data using an encryption key that is associated with this version and causes the particular positioning support device to transmit the assembled and encrypted data. The positioning support device transmits the data. An apparatus obtains the data, received by a mobile device, and attempts to decrypt the data using at least one encryption key. If the decryption is successful with a particular encryption key, a version of a set of values of parameters may be selected that is associated with the encryption key.