Counter mode encryption for FNBDT/MELP

Counter mode encryption is the proposed method for encrypting Mixed Excitation Linear Predictor (MELP) data for the Future NarrowBand Digital Terminal (FNBDT). Counter mode encryption employs an indefinite keypad generated by an encrypting function applied to a counter. The clear (unencrypted) data is exclusive-or-ed with the next available key in the pad. When encrypted data is received, the clear data may be retrieved by exclusive-or-ing the encrypted data with the same key used for encryption. The benefits and drawbacks of implementing counter mode encryption for real time MELP audio applications are presented.