1. A method of efficiently transmitting secure digital speech, comprising: digitally encoding speech audio into a plurality of data frames; classifying the data frames haying a bit size meeting or exceeding a predetermined threshold as containing encoded speech, and classifying the data frames having a bit size below the threshold as not containing encoded speech; encrypting the data frames containing encoded speech; not encrypting the data frames not containing encoded speech; assembling the encrypted and non-encrypted data frames into one or more Media Access Control (MAC) Packet Data Units (PDU); setting an encryption indicator in the header of each MAC PDU containing an encrypted data frame; and transmitting the MAC PDUs.