A first subscriber unit (SU) operating in a two-way radio frequency (RF) communications system having at least one fixed terminal, one or more channels, and a plurality of subscriber units, generates a first burst of data for transmission to the at least one fixed terminal. The first SU calculates a cyclic redundancy check (CRC) or checksum value over (i) at least a first portion of the first burst of data and (ii) at least a portion of a first private data. The first SU transmits the first burst of data and the calculated CRC/checksum value, but not the first private data, to the at least one fixed terminal. The fixed terminal then calculates its own CRC/checksum over the received burst and its own copy of the first private data, and compares the result with the received CRC/checksum. The fixed terminal authenticates the received burst if the values match.