Abstract: A satellite communications system apparatus and method for authenticating data transmissions uses the position of the transmitter, which position is determined by the satellite communications system. The transmitter position information is appended to the message (which can be either clear text or encrypted), which is sent to the receiver at a second location by the satellite system. A receiver can then authenticate the received message by comparing the received transmitter position with stored transmitter position information. The mobile transceiver syncing versions of the present invention allow the transceiver to be mobile, as opposed to being stationary. In this mobile version, each succeeding message is encrypted using the previous position of the mobile transceiver. Examples of transceivers implementing the apparatus and method of the present invention are shown, as are the specific vertical market applications of financial networks and automatic weather observation and reporting systems.